Pulmonary System

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PULMONARY SYSTEM

Elizabeth Flasch, Nicole Brueck, Justin Lynn, and Jennifer Henningfeld

DEVELOPMENTAL ANATOMY OF THE PULMONARY SYSTEM

A. Embryology of the Lung

In humans, there are five well-recognized stages of lung development: embryonic, pseudoglandular, canalicular, saccular, and alveolar (Figure 2.1).

1. Embryonic Stage. Day 26 to 52—In primitive development, the foregut forms a lung bud from the pharynx 26 days after conception. This lung bud elongates and forms the trachea and two bronchial buds, which then separate from the esophagus. By the end of the embryonic period, the larger airways, including the trachea, main stem, and segmental and subsegmental bronchi are developed. During this phase, the respiratory endothelium and diaphragm develop (Schnapf & Kirley, 2010).

2. Pseudoglandular Stage. Day 52 to week 16—During this stage, branching morphogenesis continues, leading to the formation of subsegmental bronchi, bronchioles, and primitive acinar tubules. Cilia appear on the surface of the epithelium of the trachea and the main stem bronchi at 10 weeks of gestation and are present on peripheral airways by 13 weeks gestation. Lymphatics appear in the lung itself by week 10. Goblet cells appear in the bronchial epithelium at 13 to 14 weeks gestation (Schnapf & Kirley, 2010).

3. Canalicular Stage. Week 17 to 26—This stage is so named because of the appearance of vascular channels, or capillaries, which begin to grow by forming a capillary network around the air passages. By the end of this period, pulmonary acinar units are formed, consisting of a respiratory bronchiole, alveolar ducts, and alveolar sacs. By 20 to 22 weeks of gestation, type I and type II epithelial cells can be differentiated. By the end of this period, the development of the air–blood barrier is thin enough to support gas exchange. These developments, along with increasing synthesis of surfactant, are critical to the extrauterine survival of the fetus. At 22 to 24 weeks gestation, the survival of the fetus becomes possible during this stage (Schnapf & Kirley, 2010).

4. Saccular Stage. Week 26 to 36—During this period, there is a marked increase in the potential gas-exchanging surface area due to thinning of the epithelium and mesenchyme and further formation of the capillary net. The terminal structures are referred to as saccules and are relatively smooth-walled cylindrical structures. They then become subdivided by ridges known as secondary crests. As the crests protrude into the saccules, part of the capillary net is drawn with them, forming a double capillary layer. Further septation between the crests results in smaller spaces termed subsaccules (Schnapf & Kirley, 2010).

5. Alveolar Stage. Week 36 and beyond—Alveolarization is rapidly progressing during this period. Alveologenesis is characterized by a complex interaction of epithelial, fibroblast, and vascular growth factors with extracellular matrix components (Schnapf & Kirley, 2010).

6. The First Breath. The thorax is compressed as it passes through the birth canal, forcing out some of the fetal lung fluid. Chest recoil after the thorax is delivered results in air entry into the lungs. The first inspiratory effort must be large enough to overcome the viscous resistance to movement of the intrapulmonary liquid and overcome the tissue and surface tension. For the first several minutes to 2 hours, expiration is often incomplete, resulting in progressively increasing functional residual capacity (FRC). For infants born by cesarean section, it takes longer to establish FRC (Schnapf & Kirley, 2010).

B. Postnatal Lung Development

Normal lung growth is a continuous process that begins early in gestation and extends through infancy and childhood. Estimates of alveolar number at birth vary greatly but the general accepted number is 50 million. Eventually 300 million alveolar will form after birth. Lung volume will increase 23-fold, alveolar number will increase sixfold, alveolar surface area will increase 21-fold, and lung weight will increase 20-fold. Alveolar development is thought to continue through early childhood with implications for recovery of lung function after certain childhood insults (Schnapf & Kirley, 2010).

FIGURE 2.1 Embryonic development of the lungs.

C. Upper Airway Development

The upper airway is responsible for warming, humidifying, and filtering air before it reaches the trachea. There are notable differences between pediatric and adult airways (Table 2.1).

1. Nose

a. Embryology. Nasal cavities begin as widely separated pits on the face of the 4-week-old embryo. The ethmoid and the maxillary sinuses form in the third to fourth gestational month and, accordingly, are present at birth. The sphenoid sinuses are generally pneumatized by 5 years of age; the frontal sinuses appear at age 7 to 8 years but are not completely developed until late adolescence. The ethmoid cells are present and increase in size throughout life. Frontal and sphenoid sinuses do not begin to invade the frontal or sphenoid bones until several years after birth (Walsh & Vehse, 2010).

b. Until the age of 6 months, infants are obligatory nose breathers because the elongated epiglottis, positioned high in the pharynx, almost meets the soft palate. However, they are still able to mouth breathe because blocked nares do not lead to complete upper airway obstruction. By the sixth month, growth and descent of the larynx reduce the amount of obstruction. Nasal breathing doubles the resistance to airflow and proportionately increases the work of breathing (WOB; Walsh & Vehse, 2010).

2. Pharynx

a. Embryology. The oropharyngeal membrane between the foregut and the stomodeum begins 37to disintegrate to establish continuity between the oral cavity and the pharynx in the 4-week-old embryo (Walsh & Vehse, 2010).

TABLE 2.1 Anatomic Differences Between Pediatric and Adult Airways

Pediatric Anatomic Difference	Clinical Significance
Proportionally larger head	Increases neck flexion and obstruction
Smaller nostrils	Increases airway resistance
Larger tongue	Increases airway resistance
Decreased muscle tone	Increases airway obstruction
Longer and more horizontal epiglottis	Increases airway obstruction
More anterior larynx	Difficult to perform blind intubation
Cricoid ring is the narrowest portion	Inflated cuffed tubes not recommended for routine intubation in children younger than 8 years of age
Shorter trachea	Increases risk of right main stem intubation
Narrower airways	Increases airway resistance

b. The pharynx is a musculomembranous tube that extends from the base of the skull to the esophageal and laryngeal inlets. The pharynx is the conduit for inhalation and exhalation and is vital to the production of speech. The nasopharynx is located above the soft palate. The oropharynx extends from the soft palate to the level of the hyoid bone. The hypopharynx extends from the level of the hyoid bone to the esophageal inlet (Walsh & Vehse, 2010).

3. Larynx

a. Embryology. During the fourth week of embryologic life, the laryngotracheal groove begins as a ridge on the ventral portion of the pharynx. Vocal cords begin to appear in the eighth week. In the newborn infant, the larynx is approximately at the level of the second cervical vertebra. In the adult, the larynx is opposite the fifth and sixth cervical vertebrae (Walsh & Vehse, 2010).

b. The larynx is a funnel-shaped structure that connects the pharynx and trachea. It includes the thyroid cartilage, vocal cords, epiglottis, and the cricoid cartilage. It is important in the production of the cough and protects the airway from aspiration of food during deglutition (Walsh & Vehse, 2010).

c. Compared with the adult epiglottis, the child’s epiglottis is longer and more flaccid. The epiglottis in a newborn extends over the larynx at approximately a 45-degree angle. This more anterior and cephalad epiglottis may make intubation of the airway more difficult in the small infant (Walsh & Vehse, 2010).

d. The cricoid cartilage ring is the only point in the larynx in which the walls are completely enclosed in a circumferential ring of cartilage. In the rest of the trachea, the incomplete C-shaped cartilaginous rings are located anteriorly and laterally and the posterior wall is membranous. Resistance to airflow is inversely proportional to the fourth power of the radius. Thus, swelling from trauma or infection can produce large increases in airway resistance (Walsh & Vehse, 2010).

e. Vocal cords must abduct to allow inhalation and exhalation and adduct to prevent aspiration (Walsh & Vehse, 2010).

4. Trachea

a. Embryology. The trachea begins to develop in the 24-day-old embryo. At 26 to 28 days, a series of asymmetric branchings of the primitive lung bud initiate the development of the bronchial tree (Walsh & Vehse, 2010).

b. The trachea is a thin-walled rigid tube flattened posteriorly that is characterized by a framework of 16 to 20 cartilages that encircle the trachea, except in its posterior aspect, which is membranous and contains smooth muscle.

c. The trachea’s nervous, vascular, and lymphatic supplies are independent of those in the lungs.

D. Lower Airway Development (Figures 2.2 and 2.3)

1. Lung

a. At birth, the lungs weigh about 40 g and double in weight by 6 months. By age 2 years, they weigh about 170 g. Normal adult lungs weigh approximately 1,000 g.

b. The right lung has three lobes, and the left has two lobes separated by divisions called fissures, each further subdivided into bronchopulmonary segments. The surface of the lung is covered with the visceral pleura.

2. Conducting Zone

a. Intrapulmonary airways are divided into three major groups: cartilaginous bronchi, membranous bronchioles, and gas exchange units.

i. Cartilaginous bronchi are the large airways that include nine to 12 divisions terminating in bronchi having a diameter of approximately 1 mm.

ii. Membranous bronchioles comprise an additional 12 divisions before ending as terminal bronchioles, the last conducting structure in the lung.

FIGURE 2.2 Epithelial and endothelial development.

FIGURE 2.3 Upper and lower airway anatomy.

b. The airways are lined with an epithelial membrane, which gradually changes from ciliated pseudostratified columnar epithelium in the bronchi to a ciliated cuboidal epithelium near the gas exchange units.

c. In the largest airways, a smooth muscle bundle connects the two ends of the C-shaped cartilage. As the amount of cartilage decreases, the smooth muscle assumes a helical orientation and gradually becomes thinner.

3. Gas Exchange Units (Alveoli)

a. Alveoli are complex networks in which gas exchange takes place. Alveoli are lined with two epithelial cell types. Type I cells cover about 90% of the total alveolar surface. These cells are adapted to allow for the rapid exchange of gases. Type II cells constitute the other 10% and secrete surfactant material that lowers surface tension and maintains the patency of alveoli during respiration. Alveoli patency refers to the alveoli’s ability to maintain a spherical shape, preventing collapse, which is necessary for efficient gas exchange.

b. Two types of intercommunicating channels provide collateral ventilation for the gas exchange units. Alveolar pores of Kohn are holes in the alveolar wall that provide channels for gas movement between alveoli. These pores are not present until 6 to 8 years of age. While the pores of Kohn connect alveoli to adjacent alveoli, the canals of Lambert are accessory channels in the lungs connecting some terminal bronchioles to adjacent alveoli.

c. Gas exchange involves the movement of gas between the atmosphere and the alveoli and the pulmonary capillary blood. This movement occurs via simple passive diffusion whereby the gases travel from an area of high pressure to an area of low partial pressure.

E. Thoracic Cavity

1. Diaphragm

a. The diaphragm is the principal muscle of inspiration. If the chest wall is stiff, contraction of the diaphragm during inspiration decreases the pressure within the thoracic cavity and increases thoracic volume. This negative intrathoracic pressure in the chest cavity is discussed in detail later in this chapter. The diaphragm is innervated by the phrenic nerve (third, fourth, and fifth cervical spinal nerves).

b. The diaphragm sits more horizontally in the infant than in the older child or adult.

2. The Chest Wall. The infant’s chest wall is very compliant compared with the rigid chest wall of the older child and adult. In the presence of lung disease, contraction of the diaphragm results in intercostal and sternal retractions rather than in inflation of the lungs. These retractions occur because the intercostal muscles are not strong enough to stabilize the chest against the stronger diaphragm contraction.

F. Pulmonary Circulation

The development of pulmonary circulation closely follows the development of the airways and alveoli.

1. Embryology. Preacinar arteries, which branch along the airways, develop in utero. Muscular arteries end at the level of the terminal bronchiole in the fetus and 39newborn but gradually extend to the alveolar level during childhood. Prematurely born infants have less well-developed vascular smooth muscle.

2. Pulmonary Blood Volume. The lungs receive the entire cardiac output from the right ventricle (RV) if no intracardiac right-to-left shunts are present.

3. Pulmonary Lymphatics. The lymphatic system is composed of a superficial network found in the pleura and the deep network around the bronchi and pulmonary arteries and veins. An increase in the hydrostatic pressure of the pulmonary and systemic circulation can result in effusions by decreasing the rate of pleural fluid absorption. Lymphatics may be disrupted by thoracic surgery or trauma, leading to lymphatic effusions.

DEVELOPMENTAL PHYSIOLOGY OF THE PULMONARY SYSTEM

A. Physiologic Function

The primary function of the lung is gas exchange. Its prime function is to allow oxygen to move from the air into the venous blood and for carbon dioxide to move out. Other functions include metabolizing certain compounds, filtering the blood, and acting as a reservoir for blood. During inspiration, the diaphragm contracts, the chest wall expands, and the volume of the lungs increases. Gas flows from the atmosphere into the lungs and oxygen diffuses into the blood at the alveolar–capillary interface. During expiration, the diaphragm and the chest wall relax, thoracic volume decreases, intrathoracic pressure increases, and gas flows out of the lungs. This process is affected by pulmonary compliance and resistance and by pulmonary vascular pressures and resistance (West, 2012).

1. Pulmonary Compliance and Resistance

a. Compliance (CL) is the measure of the distensibility of the lungs, influenced by surfactant and elasticity of lung tissue. The compliance of a lung depends on its size (Figure 2.4; West, 2012).

i. Volume change is produced by a transpulmonary pressure change (CL = ΔV/ΔP). For example, if the volume change produced by a given pressure change is small, the lungs must be stiff or have decreased compliance (West, 2012).

ii. Compliance of the infant chest wall (especially in premature infants) is considerably greater than that of the adult. There is less opposition to lung collapse. Compliance is decreased by pulmonary edema, pneumothorax, pulmonary fibrosis, and atelectasis. Compliance is increased by asthma, lobar emphysema, and in the normal aging lung (West, 2012).

FIGURE 2.4 Compliance curve. Compliance reflects the amount of pressure required to deliver a given volume of air into an enclosed space such as the lung. Increased compliance of a lung unit indicates that less pressure is needed to distend the lung with a given volume. Decreased compliance indicates that more pressure is required to deliver the same volume of air.

b. Airway resistance is the driving pressure of air divided by the airflow rate determined by airway diameter. It is directly proportional to flow rate, the length of the airway, and the viscosity of the gas and is inversely proportional to the fourth power of the airway radius (Poiseuille’s law; West, 2012).

i. The upper airway contributes 70% of the total airway resistance in adults and 50% of total airway resistance in infants. In infants, the small peripheral airways may contribute as much as 50% of the total airway resistance compared with less than 20% airway resistance for the adult (West, 2012).

ii. Resistance is increased by asthma, cystic fibrosis (CF), bronchopulmonary dysplasia (BPD), bronchiolitis, tracheal stenosis, and increased respiratory secretions. High resistance increases the WOB and creates respiratory distress.

2. Pulmonary Vascular Pressures and Resistance

a. Changes in pulmonary circulation at birth. The fetus has low pulmonary blood flow related to high pulmonary vascular resistance (PVR). 40This high PVR is due to hypoxic vasoconstriction, thicker pulmonary musculature, relatively low lung volumes, and smaller surface area. At birth, there is a decrease in PVR associated with ventilation and the effect of oxygen. This drop in PVR after birth increases blood flow to the lungs, thus facilitating the transition from fetal circulation. In the 6 to 8 weeks following birth, there is a further progressive fall in resistance associated with thinning of the smooth muscle layer (West, 2012).

b. Intravascular pulmonary pressure is measured by placing a catheter in the pulmonary artery and measuring systolic, diastolic, and mean arterial pressures (MAPs). The pressures in the pulmonary circulation are remarkably low. The mean pressure in the main pulmonary artery is about 15 mmHg; the systolic and diastolic pressures are about 25 and 8 mmHg, respectively (West, 2012).

c. Ventilation–perfusion matching. Regional differences in lung perfusion exist. Blood flow is lightest at the apex and increases at the base of the lung in an upright position (Figure 2.5; West, 2012).

i. Zone I is located in the apexes of the lungs of an upright adult. Mean pulmonary arterial pressure is less than alveolar pressure (West, 2012).

ii. Zone II is located in the midlung field. Here pulmonary artery pressure is greater than alveolar pressure, which is greater than pulmonary venous pressure (West, 2012).

iii. Zone III is found in the base of the lung of an upright adult. Here the pulmonary artery and venous pressures are greater than alveolar pressure (West, 2012).

FIGURE 2.5 Ventilation–perfusion relationships.

d. PVR can be calculated by dividing the pressure across the lungs by the pulmonary blood flow. A decrease in resistance to blood flow can occur only through an increase in the blood vessels’ diameters or an increase in the number of perfused vessels, that is, an increase in the cross-sectional diameter of the pulmonary vascular bed. An increase in cardiac output decreases the calculated PVR. The interrelationship between lung volume and PVR is complex and is influenced by pulmonary blood volume, cardiac output, and initial lung volume. Active changes in PVR can be mediated by neurogenic stimuli, vasoactive compounds, or chemical mediators (West, 2012). The pulmonary vascular resistance can be calculated as

This equation is conceptually equivalent to the following:

R = ΔP/Q

where R is the PVR, ΔP is the pressure difference across the pulmonary circuit, and Q is the rate of blood flow through it.

3. Control of Breathing

a. Central respiratory centers. The medullary respiratory center is essential for the generation of the respiratory rhythm. In addition, the medulla is associated with inspiration and expiration. The pons contains the apneustic center and pneumotaxic center responsible for “fine tuning” the respiratory rhythm.

b. Cortex. Within limits, the cortex can override the function of the brainstem.

c. Other parts of the brain. The limbic system and hypothalamus can alter the pattern of breathing during emotional states (including rage and fear).

d. Peripheral neural reflexes. Respiratory mechanoreceptors that can affect respiration are located within the upper airways, trachea, and lungs. Impulses are transmitted to the brainstem respiratory centers via the vagus nerve.

e. Chemical control of respiration (Figure 2.6)

i. Central chemoreceptors: The central chemoreceptors are surrounded by brain extracellular fluid and respond to changes in its H⁺ ion concentration. An increase in H⁺ concentration stimulates ventilation, whereas a decrease inhibits it. The composition of the extracellular fluid around the receptors is governed by the cerebrospinal fluid (CSF), local blood flow, and local metabolism. Of these, the CSF is the most important.

FIGURE 2.6 Chemical control of breathing.

PCO₂, partial pressure of carbon dioxide; PO₂, partial pressure of oxygen.

ii. Peripheral chemoreceptors: These are located in the carotid bodies at the bifurcation of the common carotid arteries and in the aortic bodies above and below the aortic arch. The carotid bodies are the most important in humans.

4. Mechanics of Breathing. Elastic properties of the lung come from the elastic tissue and collagen that support the lungs’ internal structures. Lung compliance changes with age. The thorax of the infant is much more compliant than that of an adult.

5. Lung Volumes (Figure 2.7; West, 2012)

a. Total lung capacity is the total volume of the gas contained in the lung at maximum inspiration.

b. Vital capacity (VC) is the maximum volume expired from the total lung capacity with maximal expiration.

c. FRC is the volume of gas remaining in the lung after a normal expiration.

d. Residual volume is the volume of gas remaining in the lung following a maximal respiratory effort.

B. Gas Exchange and Transport

Respiratory gas exchange involves the movement of gas from the atmosphere to the alveoli to the pulmonary capillary blood. The alveolar capillary membrane permits the transfer of oxygen and carbon dioxide while restricting the movement of fluid from the pulmonary vasculature to the alveoli.

1. Diffusion

a. Oxygen diffuses from the alveolus through the alveolar epithelial lining, basement membrane, capillary endothelial lining, plasma, and red blood cell. Blood passing through the lung resides in a pulmonary capillary for only 0.75 second. Diffusion of oxygen depends on the difference (gradient) between alveolar and oxygen tension (West, 2012).

FIGURE 2.7 Lung volumes.

b. Carbon dioxide diffuses from the red blood cell to the plasma, through the capillary endothelial lining, basement membrane, and alveolar epithelial lining. The pulmonary capillary mean alveolar carbon dioxide gradient is smaller than that of oxygen (i.e., CO₂ diffuses more readily than O₂; West, 2012).

2. Oxygen Transport

a. Oxygen is carried in the blood in two forms: in combination with hemoglobin (Hgb) and dissolved in plasma. The arterial oxygen content (CaO₂) describes the total amount of oxygen carried by arterial blood. Parameters are defined and other oxygen values are calculated in a similar fashion as in Table 2.2. CaO₂ is represented in the following equation (West, 2013):

(Hgb × 1.34 × SaO₂) + (0.003 × PaO₂)

b. Oxyhemoglobin dissociation curve (Figure 2.8)

i. The oxyhemoglobin dissociation curve is an S-shaped curve with Hgb on the y-axis and PaO₂ on the x-axis. The release of oxygen to the tissues is directly related to Hgb concentration and the affinity of oxygen for Hgb. Thus, on the steep portion of the dissociation curve, relatively small changes in PaO₂ cause large changes in oxygen saturation of Hgb (West, 2012).

ii. A shift to the right, which facilitates the unloading of oxygen from Hgb, is caused by a decrease in pH, an increase in PaCO₂, elevated temperature, or an increase in 2,3-diphosphoglycerate (2,3-DPG). 2,3-DPG decreases the affinity of Hgb for oxygen. During hypoxia or anemia, oxygen availability is increased within a matter of hours by an increase in 2,3-DPG (West, 2012).

iii. A shift to the left, which increases the binding of oxygen to Hgb, is caused by an increase in pH, a decrease in PaCO₂, a decrease in temperature, or a decrease in 2,3-DPG. Fetal Hgb has decreased 2,3-DPG, shifting the curve to the left of the adult Hgb curve. Thus, at a given PaO₂ and hematocrit, fetal Hgb is more readily saturated than adult blood is. Fetal Hgb also releases oxygen less readily to the tissues than adult Hgb. Fetal Hgb is replaced by adult Hgb within 4 to 6 weeks after birth (West, 2012).

3. Cellular Respiration. All cells depend on a continuous supply of oxygen to support aerobic metabolism. Oxygen delivery data do not provide information about the adequacy of tissue oxygenation. In septic shock, tissue oxygen extraction is altered. To assess tissue oxygen extraction, a true mixed venous blood sample should be obtained from the pulmonary artery.

43TABLE 2.2 Normal Oxygenation Profile Values

Parameter	Calculation	Norms
CaO₂	CaO₂ = (Hgb × 3.4 × SaO₂) + (PaO₂ × 0.003)	20 mL/dL
CvO₂	CvO₂ = (Hgb × 3.4 × SvO₂) + (PvO₂ × 0.003)	15 mL/dL
a-vDO₂	CaO₂ = CvO₂	3.5–5 mL/dL
DO₂	DO₂ = CaO₂ × Cl × 10	620 ± 50 mL/min/m²
VO₂	VO₂ = (CaO₂ – CvO₂) × Cl × 10	120–200 mL/min/m²
O₂ER	(CaO₂ − CvO₂)/CaO₂ × 100	25% ± 2%
SvO₂		75% (60%–80%)

a-vDO₂, arteriovenous oxygen difference; CaO₂, arterial oxygen content; CI, cardiac index; CvO₂, venous oxygen content; DO₂, oxygen delivery; Hgb, hemoglobin; O₂ER, oxygen extraction ratio; PaO₂, arterial oxygen partial pressure; PvO₂, venous partial pressure of oxygen; SaO₂, arterial oxygen saturation; SvO₂, venous oxygen saturation; VO₂, oxygen consumption.

FIGURE 2.8 Oxyhemoglobin dissociation curve.

PaO₂, arterial oxygen partial pressure.

CLINICAL ASSESSMENT OF PULMONARY FUNCTION

A. History

1. Prenatal and Delivery

a. Birth weight

b. Gestational age

c. Apgar scores

d. Respiratory distress in the neonatal period, including oxygen requirements and ventilatory assistance

e. Length of hospital stay

2. Childhood

a. Verify immunization history and tuberculosis (TB) tests

b. Family history of asthma, allergies, eczema, respiratory illnesses

c. Episodes of wheezing with previous illness

d. Frequency of colds and upper respiratory tract infections

e. Has the child every been intubated

f. Environmental exposure to smoke, molds, or pets

g. Supervise child, especially younger than 5 years, to evaluate risk of foreign-body aspiration

h. Recent illnesses of child or family members

i. Recent emergency room visits and/or hospitalizations

j. Use of medications, medications to treat respiratory symptoms, and nonprescription and alternative medications

k. Recent international travel

3. Other Significant Information

a. Chest pain (rarely of cardiac origin) is described in quality, timing with respiratory phase, duration (continuous or intermittent), and precipitating factors.

44b. Growth and development. Failure to gain weight is often the first sign of chronic pulmonary disease. Activity level or milestones may be delayed with chronic pulmonary dysfunction.

c. Gastrointestinal (GI) symptoms

i. Pneumonic processes frequently manifest as generalized abdominal pain in young children.

ii. Acute or chronic infection may cause anorexia and occasional vomiting.

iii. Upper airway mucus may impede swallowing and cause gagging, vomiting, or diarrhea in infants and toddlers.

iv. Bulky, foul-smelling stools may indicate CF.

v. Gastroesophageal reflux may cause chronic pulmonary aspiration.

d. Sleeping habits

i. Evaluate duration of sleep at night and causes of interruptions.

ii. Nighttime coughing is a frequent symptom of asthma or other lower respiratory tract diseases.

iii. Note positioning for sleep, such as head flat or requiring head elevation.

iv. If a humidifier is used, note care and maintenance of the humidifier.

v. Note signs of obstructive sleep apnea, such as sleeping propped up on pillows, apnea, orthopnea, and snoring.

B. Physical Examination

1. Inspection

Anatomic landmarks of the thorax provide a method for describing physical examination findings (Figure 2.9).

a. Thoracic inspection

i. Note thoracic contour: A neonate’s chest is round with the anteroposterior diameter equal to the transverse diameter. Chest contour is more oval by 2 to 3 years of age. Disproportionate size may be detected by comparing head circumference (occipitofrontal circumference [OFC]) to chest circumference. From birth to 2 years, the head and chest circumferences are generally equal. During childhood, chest size 45is 5 to 7 cm greater than the OFC. Chronic disease may cause enlarged anteroposterior diameter or “barreled chest” which is similar to the neonate’s chest contour (Figure 2.10).

FIGURE 2.9 Anatomic landmarks of the thorax. The lower lobes of both lungs have only small projections on the anterior plane on the x-ray film and can be better visualized on a lateral or posterior x-ray film. The midaxillary line, midclavicular line, vertebral line, and intercostal spaces are frequently used landmarks in describing the location of pulmonary findings. (A) Anterior view: Left lung is divided into two lobes by the left oblique fissure. The right lung is divided into three lobes by the horizontal fissure with landmarks between the fourth rib medially and the fifth rib laterally. The right oblique fissure is found from the inferior margin (midclavicular line) to the fifth lateral rib. (B) Posterior view: Fissures dividing upper and lower lobes begin at T3, medially, extending in a line inferiorly below the inferior tips of the scapula.

ii. Note any skeletal deformities: Anomalies, such as sternal depression (pectus excavatum) or protrusion (pectus carinatum), may cause or be associated with respiratory abnormalities by altering pulmonary mechanics. Inspect posterior thoracic structures and the spine. Kyphosis and scoliosis can impair pulmonary mechanics.

iii. Note symmetry of excursion (depth of respiration).

b. Respiratory effort

i. Rate and rhythm are age related: Respiratory rate is about one fourth of the pulse rate in the normal infant at rest.

ii. Evaluate the adequacy of thoracic excursion.

iii. Note the effort of breathing: Infants and young children breathe principally with the diaphragm because of immature intercostal muscles. Infants in respiratory distress may exhibit nasal flaring, head bobbing, expiratory grunting, or head extension.

iv. Note the use of accessory muscles: Signs of respiratory insufficiency include suprasternal, substernal, intercostal, and subcostal retractions.

FIGURE 2.10 Thoracic contours by age. Illustrates the comparison of the anteroposterior diameter and contour of the chest wall according to age.

v. Variations in respiratory patterns are also observed with various neurologic abnormalities (Figure 2.11).

vi. Note the quality of the voice and breathing; pay particular attention to a muffled voice; stridor; expiratory/inspiratory wheezing; and a barky, loose, congested, or paroxysmal cough.

c. Skin color and appearance

i. Cyanosis is observed when 3 to 5 g of Hgb becomes desaturated. Conditions that can mask or mimic cyanosis include hypothermia, anemia, or polycythemia. If cyanosis persists with oxygen administration, this may indicate the presence of an intracardiac shunt.

ii. Clubbing of fingertips is an indication of chronic hypoxia. The distal phalanx is flat and broad, causing a “club” appearance.

iii. Cyanosis is not related to increased PaCO₂ (hypercarbia). A patient may be well oxygenated with a supplemental flow of oxygen diffusing through the airway but still be significantly hypercarbic and without a cyanotic appearance.

2. Palpation

a. This is a limited technique in infants, but can be useful in older children.

b. Expand the hands bilaterally and symmetrically across the anterior chest wall and then across the posterior chest wall to evaluate the following:

i. What is the expansion of the thoracic cage?

ii. Fremitus is conduction of the child’s voice while the child says, for example, “99.” Vibrations should be noted at the trachea and upper airway. Decreased sensation is normally observed centrally near large airways, otherwise it is associated with occlusions. Increased sensation is associated with solid masses (consolidations). In infants, palpation during crying allows a similar evaluation.

c. Palpation of fine vibrations may indicate underlying pleural friction rub.

d. Palpate the entire thoracic cage for crepitus, a coarse, crackly feeling (and sound) of air in the subcutaneous tissue.

e. With a history of trauma, evaluate the skeletal structure, especially the clavicles.

f. Palpate the tracheal position (midline); if it is shifted, locate the position of maximal impulse of the heart. A shift in either or both may indicate fluid or air collection or a collapsed lung.

FIGURE 2.11 Variations in respiratory patterns. Breathing patterns as associated with anatomic regions of the brain. Lesions causing global injury tend to cause an orderly progression of respiratory patterns down to the brain stem. Focal lesions may cause a lower CNS pattern; higher function is otherwise noted on examination.

CNS, central nervous system; HTN, hypertension; V_T, tidal volume.

3. Percussion

a. Technique used to determine the presence of air, fluid, or masses in the underlying lung and to determine anatomic landmarks (such as the upper margin of the liver; Figure 2.12).

b. Percuss using the middle finger of one hand flush against the chest wall in interspaces, noting the quality of sound produced by striking this finger with the middle finger of the other hand.

i. Right side of the anterior chest: Percussion sounds should be resonant in each intercostal space down to the fifth to sixth intercostal space, where the superior liver margin begins. There the sound changes and has a dull quality. Farther down where the lung field ends and the liver border continues, the percussion note goes flat.

ii. Left side of the anterior chest: Percussion of the heart borders can be determined. The superior border is often percussed between the second and third intercostal spaces. The inferior border is at the fourth to sixth intercostal spaces, and the left border is just lateral to the midclavicular line. At the sixth intercostal space and below, tympany may be observed because of an air-filled stomach.

FIGURE 2.12 Percussion of the thorax. Differences in densities are noted to detect the presence of abnormal air, fluid, bones, or mass.

iii. Posterior chest: Percuss side to side to identify abnormal densities.

c. Variations in sounds define the density of structures:

i. Flat: Short, soft; heard over bone

ii. Dull: Medium pitch; duration heard over the liver, spleen, and mass densities

iii. Resonance: Low, loud, and long; heard over an air-filled lung

iv. Hyperresonance: Deep pitched, loud, and prolonged; heard over an overinflated lung or air collections such as pneumothorax

v. Tympany: High, musical quality, loud; heard over gas-filled organs such as the stomach

4. Auscultation

a. Evaluate the pitch, intensity, quality, and duration of each phase using the diaphragm of the stethoscope. For small infants, using either a small diaphragm or the bell of a stethoscope may enable localization of sounds.

b. Compare side to side, starting at the apex and proceeding methodically to the bases. The thin-walled chests of infants create transmitted breath sounds throughout the lung fields. Listen for discreet changes from one location to the next. For emergent situations, a quick check under each axilla (rather than the upper lobes of the lungs) allows gross determination of the presence of bilateral aeration.

c. Quality of pitch. Vesicular breath sounds (inspiratory [I] >expiratory [E]) are of long inspiration, low pitch, and soft intensity and are heard over most of the lungs. Bronchial breath sounds (I <E) have an equal or longer expiratory phase; are high pitched, loud, and blowing; and are heard over the large airways. Bronchial breath sounds are abnormal when heard over the peripheral lung tissue. Bronchovesicular breath sounds (I = E) are high-pitched tubular sounds.

d. Adventitious sounds are abnormal sounds superimposed on normal breath sounds. Abnormal sounds have classically been defined as rales, rhonchi, and wheezes. However, confusion over definitions has prompted a focus on describing the quality and location of these sounds to associate them with common causes. Attention should be given to pitch, timing (I or E), location, and whether they clear with cough.

e. Fine, high-pitched crackling noises (similar to the sound of rolling hair between fingers) may be heard at end inspiration over peripheral lung fields in pneumonia and pulmonary edema. Medium-pitched crackles are heard in early to midinspiration with pulmonary edema and 48diffuse secretions in the bronchioles. These may partially clear with coughing. Upper airway secretions may cause coarse, bubbling (rhonchi) sounds that clear with cough.

f. Inflamed pleural surfaces may result in a very fine, low-pitched crackle over the focal areas of the chest during both I and E phases. With cessation of breathing, the crackles are not heard.

g. Wheezing results from narrowed airway lumina. Inspiratory wheezing usually results from high obstruction, such as laryngeal edema or foreign bodies. Expiratory wheezing often results from lower obstruction, such as with bronchiolitis, severe asthma, or chronic obstructive lung disease.

h. Diminished or absent breath sounds are noted as the focal absence of sounds with occasional crackling, or as an abnormal quality or abnormal location of normal sounds. This may occur with severe asthma, atelectasis, pneumothorax, or pleural fluid accumulation. This finding is usually an ominous sign.

C. Abnormal Physical Examination Findings

1. Stridor (Table 2.3)

a. Description. Stridor is noisy breathing caused by increased turbulence of airflow through a lumen.

i. Inspiratory stridor is related to the inward collapse of structures during inspiration. It is most common with supraglottic or glottic lesions because of the negative pressure generated during inspiration. Inspiratory stridor is common in laryngotracheomalacia and viral croup. Postextubation endotracheal tube (ETT) trauma is another possible source of stridor.

49ii. Expiratory stridor is most commonly observed with subglottic lesions.

iii. Fixed lesions (e.g., subglottic stenosis) may cause both inspiratory and expiratory stridor.

b. Evaluation of the child with stridor includes checking nasal patency, the size of tongue and mandible, the quantity of oropharyngeal secretions, the presence of drooling, the quality of phonation, head and neck range of motion, evidence of tooth evulsion or oral trauma, presence of fever or infectious symptoms, neurologic status, and the rate of progression of symptoms.

i. Note the position of preference. Infants with laryngomalacia, micrognathia, or macroglossia often have less distress when placed in a prone position. Children with epiglottitis or croup (laryngotracheobronchitis) often position themselves upright; children with moderate obstruction may exhibit forward extension of the head.

2. Cyanosis

a. Description. Central or peripheral blue discoloration of skin tissue caused by desaturated Hgb. Cyanosis is usually not appreciated until 3 to 5 g Hgb per deciliter of serum is desaturated, corresponding to an SaO₂ of 80% to 85% in a normal child. Cyanosis is not caused by an elevated PaCO₂. Cyanosis can be caused by other nonpulmonary conditions (Figure 2.13).

b. Cyanosis may be masked by anemia, causing a more pallid color; or polycythemia, which may create a more “ruddy” color.

c. Evaluation of the cyanotic child

i. Oxygen should be administered before proceeding with the evaluation. Note the response to oxygen and the general degree of distress. If distress is moderate or severe, emergency management should be given before proceeding with further evaluation.

ii. Note whether cyanosis is peripheral (nail beds), central (lip and tongue color), or both.

iii. Assess pulmonary function to identify upper or lower airway causes, including the presence or absence of stridor, phonation, use of accessory muscles, and general state of alertness and activity level.

iv. Obtain historical information such as the evolution of the cyanosis (sudden or gradual onset) and associated factors such as illness or decreased environmental temperature.

FIGURE 2.13 Etiology of cyanosis.

AV, arteriovenous; CNS, central nervous system; CV, cardiovascular; NB, newborn.

503. Cough

a. Description. A cough is an attempt to clear the airway of particulate matter or may result from general tissue irritation. It is produced by a reflex response in cough receptors, found in ciliated epithelium, or it may be initiated in higher cortical centers.

b. Evaluation

i. Many causes of cough are age specific (Table 2.4).

ii. Note historical information such as the presence or absence of infectious disease or exposures.

iii. Characteristics of the cough may suggest the cause:

1) Loose and productive. CF, bronchiectasis, asthma

2) Croupy. Viral laryngotracheobronchitis

3) Paroxysmal. Pertussis, mycoplasma, foreign body, chlamydia

4) Brassy. Tracheitis, upper airway drainage, psychogenic

5) Nocturnal. Asthma, sinusitis, gastroesophageal reflux, upper respiratory tract disease

6) During exercise. Asthma, CF, bronchiectasis

7) Loud honking that disappears with sleep: Psychogenic

TABLE 2.4 Common Causes of Cough by Age Groups

Neonates	Infections Chlamydia Viral: cytomegalovirus, rubella, pertussis Congenital malformations TEF Vascular rings Airway malformations
Infants	Causes mentioned for neonates plus Viral bronchiolitis Diffuse interstitial pneumonia Gastroesophageal reflux CF
Preschoolers	Infections in suppurative disease (e.g., CF) Viral infections with or without reactive airway disease Foreign body aspiration Environmental pollutants Gastroesophageal reflux Reactive airway disease
School age/adolescents	Reactive airway disease Mycoplasma pneumoniae infection CF Cigarette smoking Psychogenic cough tic Pulmonary hemosiderosis

CF, cystic fibrosis; TEF, tracheoesophageal fistula.

iv. Other associated symptoms. Examine sputum samples for white blood cells (WBCs) or eosinophils. Note hemoptysis. Poor weight gain, steatorrhea, and cough are strongly suggestive of CF.

v. A cough that persists longer than 2 weeks or a cough that causes immediate respiratory distress warrants investigation.

INVASIVE AND NONINVASIVE DIAGNOSTIC STUDIES

A. Diagnostic Approach

1. Individualization of Evaluation. All sick children are at higher risk for respiratory insufficiency or failure than adults because of the age-related anatomic differences described previously. Monitoring of pulmonary function can be individualized according to the acuity of illness and the age of the child. For a patient with the lowest acuity, clinical examination and serial observations are adequate, but with increasing severity of illness, other monitoring devices should be used. The options for monitoring include continuous observation and clinical examination, oxygen monitoring, CO₂ monitoring, monitoring of pulmonary function, and laboratory and roentgenographic studies.

2. Immediate Assessment and Care. A brief estimation of the severity of distress should be made to determine whether oxygen or airway assistance is needed.

B. Baseline Respiratory Monitoring

1. Physical Examination. All children suspected of having respiratory distress should have their clothing removed for maximum observation, ensuring that ambient temperature is controlled. Refer to the clinical assessment section in this chapter for details on physical examination techniques. A quick-look observation should be done with all patients for early recognition of respiratory distress requiring emergency management. This 20-second appraisal should include level of consciousness, color, and respiratory effort.

2. Diagnostic Studies for Children in Respiratory Distress From Any Cause

a. Complete history and physical examination

b. Chest x-ray examination

51c. Sinus x-ray examinations (depending on age)

d. Simple oxygen saturation monitoring

e. Nasal cannula end-tidal CO₂ monitoring

f. Complete blood count (CBC)

g. Tuberculin skin test (TST)

h. Nasopharyngeal swab for respiratory syncytial virus (RSV) and viral panel and pertussis, if applicable

i. Diagnostic studies to consider for children in respiratory distress according to symptoms:

i. Bronchoscopy with alveolar lavage (BAL)

ii. Laboratory testing as indicated

iii. pH probe testing for suspected gastroesophageal reflux disease (GERD)

iv. Pulmonary function testing (PFT)

C. Laboratory Studies (Table 2.5)

D. Blood Gas Analysis

1. Arterial, venous, or capillary blood gas (CBG) analysis can assist in the respiratory assessment (Table 2.6). Typically, interpretation of blood gas values involves acid–base interpretation to evaluate the pH and PCO₂ values and evaluation of oxygenation, or PO₂, separately. An arterial blood gas (ABG) analysis is the traditional method of estimating the systemic carbon dioxide tension and pH, usually for the purpose of assessing ventilation and/or acid–base status. However, an ABG analysis requires a sample of arterial blood, which can be difficult to obtain. A venous blood gas (VBG) analysis is an alternative method of estimating systemic carbon dioxide and pH that does not require arterial blood sampling. A VBG analysis can be performed using a peripheral venous sample (obtained by venipuncture), central venous sample (obtained from a central venous catheter), or mixed venous sample (obtained from the distal port of a pulmonary artery catheter). CBG samples may be used in place of samples from arterial punctures or indwelling arterial catheters to estimate acid–base balance (pH) and adequacy of ventilation (PaCO₂). Capillary PO₂ measurements are of little value in estimating arterial oxygenation.

2. PaCO₂ directly reflects the adequacy of alveolar ventilation (V_A). Hypercarbia is PaCO₂ greater than 55 mmHg.

3. Oxygenation is evaluated using the PaO₂ value. Hypoxemia is an arterial PaO₂ less than 60 mmHg.

52TABLE 2.5 Summary of Diagnostic Laboratory Evaluation of Pulmonary Function

Test	Significant Associations With Altered Levels
Immunoglobulins
Norms are age-related assays.	Decreased levels of any immunoglobulin are usually associated with congenital deficiencies and patterns of infections beginning early in life. Altered levels are associated with specific causes as follows
IgA: Deficiency is associated with an increased incidence of mucosal bacterial infections
IgG: Found in blood, lymph, CSF, pleural fluid, peritoneal fluid, and breast milk; slow response (appears 1 wk after stimulus)	Myeloma Bacterial infections Collagen disorders
IgM: Intravascular; predominant first response to bacterial or viral infection; activates the complement system	Appears early in infectious course but may persist with chronic infection
IgD: Predominant activity on the surface of B cells (involving antibody formation)	Increased with chronic infections
IgE: Found in the serum and triggers release of histamine	Increased with allogenic stimulation (e.g., asthma, associated with allergenic stimulus)
Differential WBC Count
Total WBC <1 y: maximum = 20,000 1–12 y: maximum = 15,000	Infections may cause an elevated or remarkably low (<4,000/mm³) WBC count
Segmented neutrophils (PMNs) <12 y = 25%–40% ≥12 y = >50%
Band neutrophils <10%	Increase in bands associated with bacterial infections
Lymphocytes <12 y = >50% ≥12 y = <40%	Increased with specific infections such as pertussis, Epstein–Barr virus, hepatitis
Monocytes 4%–6% Eosinophils 2%–3% Basophils 0.5%
Pilocarpine Lontophoresis (Sweat Chloride Test)
Sodium <70 mEq/L Chloride <60 mEq/L Potassium <60 mEq/L	Higher levels suggest CF
Sputum or Tracheal Aspirate Cultures
Normally should have few if any PMNs and mixed flora	PMNs: 3–4+ with dominant organism is more likely to be valid indicator of infection than one with <2+ PMNs and multiple organisms
Deep tracheal secretions preferred; protected brush specimen technique
Evaluate Gram stain for presence of PMNs
Endotracheal tubes and tracheostomy tubes become quickly colonized with existing flora, which may be misleading if microbiology results are interpreted independent of other clinical indicators

CF, cystic fibrosis; CSF, cerebrospinal fluid; IgA, immunoglobulin A; IgD, immunoglobulin D; IgE, immunoglobulin E, IgG, immunoglobulin G; IgM, immunoglobulin M; PMNs, polymorphonuclear neutrophils; WBC, white blood cell.

534. Acid–base balance is indicated by the pH. Acidosis is an arterial pH less than 7.35, and alkalosis is an arterial pH greater than 7.45.

E. Radiologic Procedures for Pulmonary Evaluation

A variety of imaging techniques allow visualization of anatomy, motion dynamics, and identification of abnormalities. Frequently, a patient may require more than one imaging procedure to detail a specific anatomic site.

1. Chest roentgenography permits visualization of lung parenchyma (tissue), pulmonary vascular markings, heart silhouette, and bone densities.

2. Fluoroscopy provides evaluation of thoracic motion, particularly diaphragm movement, which is essential to the infant, and is especially useful in the evaluation of a paralyzed diaphragm.

3. CT scan is the visualization of very thin slices of tissue in a predetermined plane of dimension, enabling identification of masses, fluid accumulation, and anatomic definition. A spiral CT may provide better definition. A spiral CT is especially useful in the evaluation of a pulmonary embolus.

4. MRI uses an external magnetic field around the patient to cause rotation of cell nuclei. Imaging provides well-defined visualization of soft tissues. No radiation is involved in this procedure.

5. Ventilation–perfusion scan (V/Q scan) is obtained by injecting a radioisotope into a peripheral vein and imaging its flow through the pulmonary vessels. The V/Q scan is made following the inhalation of a radioactive gas, which distributes to aerated alveoli. Comparison between ventilated areas with perfused areas of the lung can be made, looking for “matched” segments. Although many disorders may cause a ventilation–perfusion mismatch, a complete segmental mismatch is a useful clue to the diagnosis of pulmonary embolism (PE).

6. Pulmonary angiography involves the introduction of a catheter into a peripheral vein; the catheter is guided to the right side of the heart and to the pulmonary artery trunk. Injection of contrast media with serial radiographic examinations of the pulmonary vascular bed allows definitive recognition of vascular obstruction.

7. Echocardiography utilizes ultrasound waves to detect the structures and function of the heart and its surrounding vasculature. This method serves as a standard noninvasive diagnostic screening tool for pulmonary hypertension (PH). Abnormal findings obtained through this exam may be confirmed via a more invasive heart catheterization.

RESPIRATORY MONITORING

A. Oxygen Monitoring

1. Pulse Oximetry

a. Principles of operation. The device consists of a probe that contains an infrared light source and a photodetector. Both are housed in a wraparound strip so that the light source is aligned to emit light through tissue (such as a nail bed) to the photodetector. Saturated Hgb absorbs little light, whereas desaturated Hgb absorbs a large amount of light. The photodetector measures the amount of light that crosses the tissue and with a microprocessor computes the percentage of saturated Hgb.

b. Uses. The pulse oximeter requires pulsatile tissue to provide accurate measurements. Fingers, palmar wrap (in small infants), toes, and ear clips are used. The microprocessor unit measures pulse rate and most units have a mechanism to provide a “poor signal” alert or perfusion indicator if the tissue has an inadequate pulse. It provides a stable, accurate measurement over a wide variety of physiologic conditions.

c. Limitations

i. Poor perfusion (low cardiac output states) may interfere with a stable signal.

ii. A major source of error in children is motion artifact, which causes poor tracking of the pulse. New oximeters feature an algorithm to identify both motion artifact and poor perfusion (Fouzas, Prifitis, & Anthracopoulos, 2011).

iii. With elevated carboxyhemoglobin or methemoglobin levels, the true oxygenated Hgb values are inflated because the pulse oximeter does not distinguish between Hgb saturated with oxygen and other bound molecules.

iv. When retinopathy is a concern in the neonatal population, SaO₂ may not provide any margin of safety because the PaO₂ can vary widely when oxygen saturations are greater than 90% as the result of factors that alter the oxygen dissociation curve.

v. Newborns and children with uncorrected congenital heart disease may have variance in measurements depending on the placement 54of the oximeter. In cardiac lesions with right-to-left shunting, the right hand or foot is used for preductal measurement and the left hand or foot is used for postductal measurement.

2. Transcutaneous Oxygen Monitoring

a. Principles of operation. A small, heated probe is placed on the skin surface. Localized heating increases capillary blood flow to the site. Oxygen diffuses across the skin and is measured by a thermistor in the probe.

b. Uses. Transcutaneous oxygen monitoring (PtcO₂) functions well in infants and has shown good correlation with PaO₂ measurements. It can reduce the quantity of invasive blood gas measurements and provide continuous data for patients who are either being weaned or are otherwise labile. In the past, PtcO₂ demonstrated utility in detecting hyperoxia in neonates; however, this has been demonstrated to be more readily monitored through maintaining SpO₂ between 85% and 93% (Kacmarek, Stoller, Chatburn, & Kallet, 2017).

c. Limitations. With increasing skin thickness, the accuracy of measurements diminishes. Poor perfusion and local skin hypoxia can interfere with measurements. The probe requires site change every 4 to 6 hours with a 10- to 15-minute warm-up time (and a blood gas analysis to verify measurement accuracy). Note that the heated probe may cause blisters in some infants.

3. Mixed Venous Oxygen Saturation Monitoring

a. On occasion, pediatric patients are monitored with pulmonary artery catheters for hemodynamic measurements. One type of catheter includes a fiberoptic tip that measures reflected wavelengths of light from saturated Hgb in the local (pulmonary artery) blood flow (Kacmarek et al., 2017).

b. The mixed venous oxygen saturation (SvO₂) measurement, which is usually between 65% and 80%, is a global indicator of total oxygen consumption (VO₂).

c. Either a change in oxygen supply (arterial oxygen saturation) or in oxygen demand (VO₂) will alter this measurement (see Chapter 3 for further information).

B. Carbon Dioxide Monitoring

1. Transcutaneous Carbon Dioxide Monitoring

a. Principles. A CO₂ sensor, housed in a small probe, is mounted on the skin surface to measure diffused carbon dioxide with an electrode similar to that found in standard blood gas machines. Although in the past PtcO₂ electrodes used local heat to “arterialize” the site, recent studies showed that a predictable linear relationship can be obtained with nonheated electrodes. Typically, the PtcO₂ is higher than the PaCO₂, but the gradient should remain stable.

b. Uses. In the past, consistent correlations have been documented in neonates particularly; however, recent advances in technology have expanded this technology for use in older children and adults (Kacmarek et al., 2017). After the probe is positioned and the warm-up period has passed, the monitor measurement should be compared with a simultaneous blood gas measurement to establish the gradient. After this point, blood gas measurements can be reduced until the next site rotation (usually every 4 hours).

c. Limitations

i. The sensors appear to be somewhat fragile and prone to discreet alterations, such as inadequate fluid in the sensor. If the gradient between PtcO₂ and PaCO₂ is unstable, a site change is warranted.

ii. Calibration procedures must be exact, necessitating the presence of personnel who are well trained in the operation of these monitors.

2. End-Tidal Carbon Dioxide Monitoring. The measurement of exhaled carbon dioxide gas provides direct evidence of ventilatory function. An increased carbon dioxide level is an objective parameter for the identification of respiratory failure. This can be measured with or without a waveform.

a. Principles of operation. A small device placed in the respiratory circuit (may be on a ventilator circuit, a port on an oxygen mask/bilevel positive airway pressure [BiPAP]/continuous positive airway pressure [CPAP] mask) at the proximal airway, measures expired carbon dioxide by mass spectrometry or infrared absorption. Exhaled gas passes through this device, which emits infrared light. A detector measures the light absorption in this sample. The carbon dioxide level is inversely proportional to the light absorption.

b. Uses. In the normal subject, PtcO₂ is theoretically within 2 mm of PaCO₂.

i. Alveolar hypoventilation will lead to an increase in arterial and end-tidal carbon dioxide monitoring (ETCO₂), which can be used in patients who are being weaned from mechanical ventilation. ETCO₂ detection—whether qualitative, quantitative, or continuous—is 55the most accurate and easily available method to monitor correct ETT position in patients who have adequate tissue perfusion (Kacmarek et al., 2017).

ii. An estimation of dead space ventilation can be inferred when PaCO₂ measurements and ETCO₂ are compared serially. When the dead space (V_d/V_t) increases, the gradient between PaCO₂ and ETCO₂ increases. Conversely, as ventilator adjustments are made in an attempt to improve V_A, the gradient should diminish.

iii. Carbon dioxide monitoring can be useful in patients with increased intracranial pressure (ICP) or PH in which the patient’s PaCO₂ needs to be regulated.

c. Limitations

i. The choice of sensor used for a child must be guided by its sensitivity for smaller exhaled volumes. Clinically, infants weighing less than 5 kg may not be good candidates for this device, but the final decision should be based on comparative measurements with a blood gas analysis.

ii. Additional considerations are the warm-up time required and the calibration process, which requires operator competence.

iii. During a cardiac arrest or extubation, the ETCO₂ measurement acutely disappears. However, this lack of measurement can be an indicator of quality cardiopulmonary resuscitation (CPR) and cardiac output during chest compressions. High-quality CPR is associated with improved outcomes after cardiac arrest. Animal data support a direct association between ETCO₂ and cardiac output. Capnography is used during pediatric cardiac arrest to monitor for return of spontaneous circulation as well as CPR quality. There is no pediatric evidence that ETCO₂ monitoring improves outcomes from cardiac arrest. Studies in adults suggest that ETCO₂ values generated during CPR were significantly associated with chest compression depth and ventilation rate. ETCO₂ monitoring may be considered to evaluate the quality of chest compressions, but specific values to guide therapy have not been established in children (de Caen et al., 2015).

C. Diagnostic PFTS

Critically ill children require continuous surveillance of pulmonary function. For those who are not in frank respiratory failure, clinical assessment, including respiratory rate, observation of chest expansion, and use of accessory muscles, provides an estimation of adequacy of minute ventilation (V_E). For those in distress, further measurements may be warranted. With children, standard measurements of pulmonary function may not be possible because of lack of patient cooperation.

1. Spirometry (Figure 2.14). In the cooperative child, lung volumes can be estimated with simple flow spirometers. Flow spirometers, which measure exhaled V_T, can provide an estimation of V_C and can be used for trending. In general, 80% of the V_C can be exhaled in 1 second and is called the forced expiratory volume, or FEV₁.

a. In obstructive disease, the patient is unable to breathe out fully and has both decreased V_C and FEV₁.

b. In restrictive disease, in which the lung cannot fully expand, the V_C is low, but FEV₁ is still proportionally normal (i.e., ≥80% of V_C).

c. In the weakened patient, lower volumes may be observed with a faster respiratory rate (see Figure 2.1).

2. Pressure Manometers. Both negative and inspiratory pressure (effort) can be quantified by using a manometer to provide an estimation of muscle condition. A normal school-age child should be able to generate a minimum of about 30 cm H₂O on inspiration (called negative inspiratory force [NIF]). An infant may generate an NIF of about 20 cm H₂O, although infant effort is difficult to capture; “crying effort” measurement is sometimes used, however. On expiration, a school-age child should be able to generate a pressure of at least +30 cm H₂O.

3. Measurement of Compliance

a. Lung compliance (C_L) is the measure of the distensibility of the lung and thoracic wall. It is defined as the volume change per unit of pressure change across the lung. This is expressed as ΔV/ΔP (see Figure 2.4).

b. Dynamic compliance is the relationship of the delivered (tidal) volume to the total pressure required to deliver that volume. Dynamic compliance includes both elastic recoil and airway resistance factors.

c. Static compliance. At the end of a breath, gas flow delivery is paused. The friction created by that flow disappears, causing the inspiratory pressure to drop slightly (airway plateau pressure). The ΔV/ΔP (static pressure) reflects the elastic properties of the lung (or average distensibility of all participating alveoli). Normal range is the same in an infant as in an adult: 60 to 100 mL per centimeter of H₂O. Static compliance decreases with restrictive disease and increases with obstructive disease. Serial monitoring of static compliance may facilitate identification of optimal tidal volumes (V_T), optimal positive end-expiratory pressure (PEEP), and prediction of weaning readiness.

FIGURE 2.14 Comparison of pulmonary function measurements in the person with obstructive and restrictive pulmonary disease. The ratio of FEV₁/FVC is greater than 80%. Note that in restrictive disease the ratio is normal, but the separate measurements of FEV₁ and FVC are abnormally low.

FEV₁, forced expiratory volume in the first second of exhalation; FRC, functional residual capacity; FVC, forced vital capacity.

PULMONARY PHARMACOLOGY

A. General Principles

1. Pharmacologic management of pulmonary diseases in children requires understanding of both the pharmacokinetics of the various drugs and the disease conditions for which the drugs are prescribed. Most medications have been studied in adult populations and application to children has often occurred by extrapolation of data.

2. Physiologic Differences. Infants and young children have a greater percentage of total body water, predominately extracellular fluid. The total volume of distribution of a drug, depending on solubility, occurs within intracellular, extracellular, and interstitial fluid compartments. In general, drug doses are higher per kilogram of body weight in the infant than in the adolescent or adult.

3. Underlying Pathophysiology. Decreased blood flow to major organs influences absorption, delivery of the drug to the targeted site, and elimination. Inflammation can cause an increase in regionalized blood flow with altered capillary permeability, which can result in abnormally high drug delivery to these regions. Extravascular fluid collections may provide a protein-rich reservoir for drugs, diverting them from their intended distribution site.

4. Dosing of Medications. The dosing of medication is frequently based on one of two strategies:

a. Target concentration. The basis for following this strategy is that serum concentrations for a given drug have defined both therapeutic and toxic ranges. These assays are guidelines and are not specific to an individual patient. Knowledge of pharmacokinetics is important to the successful use of this strategy.

b. Target effect. A drug is selected with a therapeutic endpoint clearly defined before administration. Dosing is titrated to achieve this effect or until toxic effects are observed. Discontinuation of the drug may be necessary if toxicity occurs or if no therapeutic effect is achieved. Many of the medications used in a critical care setting are prescribed in this manner.

575. Protein Binding. Binding of drugs to plasma proteins determines the amount of free drug available for body distribution. Although plasma albumin levels reach adult levels soon after birth, differences in the binding properties of infant albumin can influence the dosing of selected medications.

B. Routes of Drug Delivery

1. Inhaled Administration. Inhaled administration bypasses the need for absorption as with enterally administered medications. Often smaller doses are required and a more rapid onset of action can be obtained. As infants and young children have smaller lungs and airways, the delivery of medications via inhalation can be considered more difficult. In very severe cases, this route alone may not be appropriate because the drug cannot reach the affected area (Lexicomp Online, 2016; Spahn & Szefler, 2008).

2. Enteral Administration/Absorption. The enteral route of administration requires absorption from the GI tract as an initial step (Lexicomp Online, 2016; Spahn & Szefler, 2008).

a. Gastric acid secretion and motility appear to be developmentally regulated. Intestinal transit is more rapid in the infant than in the adult. Many medications might not be absorbed as completely as in the older child or adult because of the following factors:

i. Bioavailability. A drug given enterally must be bioavailable from the GI tract.

ii. An acidic pH favors absorption of acidic medications; likewise, an alkaline pH improves absorption of alkaline compounds.

iii. The rate of gastric emptying and intestinal transit affects absorption of medications. Delayed gastric emptying or rapid intestinal motility will decrease absorption. Conditions that can decrease absorption include gastroesophageal reflux, respiratory distress syndrome (RDS), and congenital heart disease.

iv. Gastric, jejunal, or duodenal feedings may alter bioavailability. Drugs administered through these tubes may bind with proteins in the feedings. Feedings may need to be stopped for a while before and after administration. Adjustment of drug doses (based on serum assay) is reliable only with consistency in the administration of the drugs and when steady-state concentrations have been achieved.

3. Parenteral Administration. Parenteral routes of administration include the subcutaneous, intramuscular, and intravenous (IV) routes. For those routes to be viable, a medication must be water soluble or in suspension. The IV route bypasses the absorption step resulting in 100% bioavailability. There is a rapid onset of action (Lexicomp Online, 2016).

C. Neuromuscular Blocking Agents

1. Description (Table 2.7). Muscle relaxants are used in the pediatric ICU (PICU) to facilitate assisted ventilation by intervening within the neuromuscular junction in one of two ways:

a. Depolarizing agents cause a continuous release and subsequent depletion of acetylcholine.

b. Nondepolarizing agents bind the receptor sites of acetylcholine so that synaptic transmission is blocked. (Lexicomp Online, 2016; Weiner, Halfaer, & Allen, 2008)

2. Indications for Use (Weiner, Halfaer, & Allen, 2008)

a. Placement of an ETT requires administration of a neuromuscular blocking (NMB) agent in many instances.

b. Control of ventilation is often needed in patients with severe respiratory disease, increased ICP, or cardiac failure.

c. Reduction of VO₂ from muscle movement can be achieved with the use of an NMB.

3. Nursing Considerations (Lexicomp Online, 2016)

a. The choice of an NMB agent depends on the purpose and intended duration of pharmacologic paralysis. All patients who will receive a paralytic drug should be given adequate sedation and analgesia.

b. Monitoring of all children who are given an NMB agent should include ECG monitoring and pulse oximetry (see the discussion in the “Respiratory Monitoring” section). Increased heart rate (increases from baseline) may be caused by pain, fear, or seizures; increased systolic blood pressure may indicate pain or anxiety; and pupil size (dilation) may indicate earlier in the chapter fear, pain, or other causes of sympathetic stimulation such as seizures.

c. An assessment of level of NMB is required on a regular basis. Intermittent peripheral nerve stimulation and drug holidays are two techniques that can be utilized.

d. Long-term use of muscle relaxants may mask pain, anxiety, and seizures. Whenever possible, scheduled withholding of paralytic medications should be done to enable adequate assessment of the patient’s awareness and condition. Prolonged use of muscle relaxants has been associated with myopathy, particularly if steroids are given concurrently.

D. Sedatives and Analgesics

1. Benzodiazepines

a. Description. Benzodiazepines are believed to cause anterograde amnesia through the inhibition of the neurotransmitter gamma-aminobutyric acid (GABA) in the limbic system. They have little or no effect on retrograde memory and have no analgesic properties. However, there is an increase in delirium with the use of benzodiazepines (Table 2.8) (Kost & Roy, 2010; Lexicomp Online, 2016; Weiner et al., 2008).

b. Indications include short-term general sedation and amnesia for procedures, long-term use for facilitating compliance with assisted ventilation, and acute therapy for seizure management.

c. Nursing considerations include the following:

i. Benzodiazepines do not provide pain relief. In many situations, use of an analgesic in conjunction with sedation should be considered.

ii. To avoid hypotension, patients should be euvolemic (well hydrated) before administration of a benzodiazepine to avoid hypotension.

iii. Prolonged administration may result in physical dependence. Withdrawal symptoms, such as anxiety, sweating, agitation, or hallucinations, may occur with abrupt withdrawal.

iv. Some patients may exhibit a paradoxical response to benzodiazepines, which worsens with escalating doses. If an agitated child is given additional doses and the agitation worsens, consideration of a paradoxical response might prompt discontinuation of the benzodiazepine.

2. Chloral Hydrate (Kost & Roy, 2010; Lexicomp Online, 2016)

a. Description. An alcohol-based sedative–hypnotic that is safe and effective in children younger than 3 years of age (not recommended in children older than 4 years or in children with neurodevelopmental disorders due to lack of efficacy). It has very limited availability in the United States, although it is still available in other countries.

b. A central nervous system (CNS) depressant. Effects are due to its active metabolite trichloroethanol, mechanism unknown.

c. Indications include use as a sedative/hypnotic prior to nonpainful therapeutic or diagnostic procedures (EEG, CT, MRI, ophthalmic exam, dental procedure, infant PFT, echocardiogram).

d. Nursing considerations. Nurses should monitor level of sedation, vital signs, and oxygen saturation prior to and during the procedure. The taste is very bitter (disadvantage).

E. Dexmedetomidine

a. Description. Selective alpha2-adrenoceptor agonist with anesthetic and sedative properties thought to be due to activation of G-proteins by alpha2a-adrenoceptors in the brain stem resulting in inhibition of norepinephrine release; peripheral alpha2b-adrenoceptors are activated at high doses or with rapid IV administration resulting in vasoconstriction. Patients continue to breathe while on dexmedetomidine and therefore it is a good choice for patients who are not mechanically ventilated (Kost & Roy, 2010; Lexicomp Online, 2016).

b. Indications. Sedation of initially intubated and mechanically ventilated patients during treatment in an intensive care setting; sedation prior to and/or during surgical or other procedures of nonintubated patients; duration of infusion should not exceed 24 hours per the manufacturers recommendations; however, many studies exist regarding its longer term usage.

c. Nursing considerations

i. Episodes of bradycardia, hypotension, and sinus arrest have been associated with rapid IV administration.

ii. Use of a loading dose is optional.

iii. Transient hypertension: This has been primarily observed during loading-dose administration and is associated with the initial peripheral vasoconstrictive effects of dexmedetomidine. Treatment is generally unnecessary; however, a reduction in infusion rate may be required.

iv. Use of infusions for more than 24 hours has been associated with tolerance and tachyphylaxis and a dose-related increase in adverse reactions.

v. When withdrawn abruptly in patients who have received more than 24 hours of therapy, withdrawal symptoms similar to clonidine withdrawal may result (e.g., hypertension, tachycardia, nervousness, nausea, vomiting, agitation, headaches).

vi. Recovery times for sedation are somewhat longer than propofol and ketamine but shorter than pentobarbital and chloral hydrate.

vii. Patients require continuous monitoring with level of sedation, heart rate, respiration, ECG, blood pressure, and pain control.

622. Morphine and Morphine-Like Opioids (Kost & Roy, 2010; Lexicomp Online, 2016)

a. Description. Opioid receptors are found in the brain and spinal cord. Five receptors have been described, but three—the mu (M), kappa (K), and sigma (S)—are the most clinically recognized targets for opiate binding:

i. M: Supraspinal anesthesia; euphoria, respiratory depression, physical dependence

ii. K: Spinal anesthesia; sedation, miosis, and respiratory depression

iii. S: CNS stimulant; dysphoria, hallucinations, respiratory, and vasomotor stimulation

iv. Most morphine-like narcotics are described as M and K agonists. Other agents work at different receptor sites, such as nalbuphine (Nubain). Nalbuphine is a K and S receptor agonist and M receptor antagonist. Administration of nalbuphine after morphine may “antagonize” or reverse some of the morphine effects because of its antagonistic effects on the M receptor.

b. Indications for analgesic medications include procedures, relief of pain from underlying disease, and continuous analgesia for facilitating assisted mechanical ventilation. Opioids are not a substitute for an anxiolytic and amnestic agents. Although sedation occurs with opioid administration, the mechanisms do not duplicate those found in conventional sedatives such as benzodiazepines.

c. Nursing considerations

i. Some opioids, such as morphine, can cause vasodilatory effects from histamine release. Histamine release is minimal with the synthetic narcotics such as fentanyl. Most opioids, except meperidine, induce a central parasympathetic stimulation and direct depression of the sinoatrial node. All opioids also cause dose-dependent respiratory depression.

ii. Routes of delivery should be individualized with the goal of using the lowest possible dosing to provide continuous relief without side effects.

iii. Fentanyl is a synthetic opioid with approximately 100 times the analgesic potency of morphine. This concentrated solution (unless adequately diluted) may increase the risk for chest-wall rigidity especially with rapid, high-dose IV administration, and decreased seizure threshold. These side effects can be seen with all opioids and are not necessarily contraindications for their use. Slower administration and lower dosing can attenuate or prevent these side effects.

iv. Prolonged use of hydromorphone during pregnancy can result in neonatal opioid withdrawal syndrome, which may be life threatening if not recognized and treated.

v. Remifentanil and alfentanil are being utilized with increasing frequency in pediatrics.

1) Remifentanil is an approved medication for maintenance of general anesthesia in ages 0 to 2 months, 1 to 12 years, and adults. It binds with stereospecific mu-opiod receptors at many sites in the CNS, increasing pain threshold, altering pain reception, and inhibiting ascending pain pathways. In pediatric patients, pharmacokinetic data showed variable age-related changes with distribution and clearance; however, no age-related changes occur with half-life.

2) Alfentanil is an analgesic adjunct for the maintenance of anesthesia with barbiturate/nitrous oxide/oxygen, analgesic with nitrous oxide/oxygen in the maintenance of general anesthesia, analgesic component for monitored anesthesia care, primary anesthetic for induction of anesthesia in general surgery when endotracheal intubation and mechanical ventilation are required (Food and Drug Administration [FDA] approved in ages older than 12 years and adults).

vi. Current research suggests that implementation of a nurse-driven sedation protocol in a PICU is feasible. Outcomes suggest that evaluation of sedation and analgesia were better after a protocol implementation; duration of mechanical ventilation and occurrence of withdrawal symptoms tended to be reduced (Dreyfus, Javouhey, Denis, Touzet, & Bordet, 2017; Neunhoeffer, et al., 2015).

3. Barbiturates (Kost & Roy, 2010; Lexicomp Online, 2016)

a. Description. Barbiturates are one of the oldest classes of sedative agents in use today. 63They provide good sedation but are not analgesic or amnestic agents. The cardiopulmonary effects are dose dependent and well defined. Several drugs are available and classified according to the duration of activity. In addition to their sedative effect, barbiturates have potent anticonvulsant properties and can decrease cerebral metabolism, thus affecting ICP.

b. Indications. Include short-term sedation for procedures and long-term sedation for ongoing management of assisted ventilation (rarely), increased ICP, and continuous procedures such as with use of the intra-aortic balloon pump (IABP). Barbiturates are not a substitute for analgesic medications unless the dosing is high enough to produce complete anesthesia.

c. Nursing considerations

i. Cardiovascular effects are dose related. With higher doses, venodilation and depressed myocardial function can occur.

ii. Pulmonary effects are also dose related, with apnea occurring in the mid dose ranges. Bag, mask, and oxygen should always be at the bedside.

iii. Most barbiturates are in an alkaline solution and therefore must be administered separately from other medications and IV solutions.

4. Ketamine (Kost & Roy, 2010; Lexicomp Online, 2016)

a. Description. Ketamine is both an analgesic and an amnestic medication. The mechanism of this drug, including S receptor stimulation, is mediated through the sympathetic nervous system causing a brief, immediate release of endogenous catecholamines. A brief increase in heart rate, blood pressure, and general stimulation are observed with administration of lower doses (0.5–2 mg/kg). It produces dissociative anesthesia in which the eyes may be open and nystagmus may be noted; even at lower doses, however, it provides intense analgesia and amnesia. Higher doses provide good anesthesia and respiratory depression, but as the patient recovers, the stimulation and dysphoria can reappear.

b. Indications. Ketamine has a minimal effect on cardiopulmonary stability at doses less than 2 mg/kg and is a good choice for unstable patients. Bronchodilation occurs (through the release of endogenous catecholamines), which makes ketamine a good agent for patients with bronchospasm. However, ketamine may increase cerebral blood flow and ICP and therefore may not be a good agent for patients with altered intracranial compliance.

c. Nursing considerations

i. Emergence phenomena are observed more often in older children and adults than in younger children. Previously, it was believed that administration of a benzodiazepine at the end of the procedure could decrease or prevent this occurrence. However, more recent data refute this belief; in fact, some children exhibit paradoxical response to benzodiazepines, causing them to be more agitated and dysphoric (Weiner et al., 2008).

ii. Although respiratory depression is dose dependent with ketamine administration, even with normal respiratory function, it is unclear whether airway reflexes are completely intact. Therefore, bag, mask, oxygen, and suction should be available at the bedside, particularly if any other sedative agents have been given with ketamine.

5. Propofol (Kost & Roy, 2010; Lexicomp Online, 2016; Weiner et al., 2008)

a. Description. Propofol is an anesthetic agent administered intravenously, with rapid onset and short duration of action. The effects are dose dependent. Propofol is provided in a lipid emulsion of soybean oil, glycerol, and egg phosphates. It has multiple properties, including bronchodilation and rapid recovery (with minimal posthypnotic obtundation), which makes it an attractive agent for deep sedation or anesthetic induction. The drug is unrelated to any of the currently used barbiturate, opioid, benzodiazepine, arylcyclohexylamine, or imidazole IV anesthetic agents. Propofol causes global CNS depression, presumably through agonism of type A gamma-aminobutyric acid (GABAA) receptors and perhaps reduced glutamatergic activity through NMDA receptor blockade.

b. Indications. In pediatrics, use is limited to procedural sedation only.

c. Nursing considerations

i. Propofol may produce hypotension by direct vasodilation.

64ii. The Academy of Allergy, Asthma, and Immunology has issued a statement that soy- and egg-allergic patients can safely receive propofol (Lexicomp Online, 2016).

iii. Anaphylactic reactions to propofol appear not to be related to soy or egg allergy.

iv. Prolonged infusions are not recommended in pediatrics.

F. Remedial Agents

1. In providing sedation, analgesia, or pharmacologic paralysis for a child, some agents exhibit predictable but unwanted effects that can be prevented or remediated pharmacologically. The following medications may be used to manage the side effects (Table 2.9).

2. Anticholinergic Agents (Atropine and Atropine-Like Medications)

a. Description. Anticholinergic agents antagonize the actions of acetylcholine, producing a central vagal blockade (tachycardia, increased blood pressure, mitosis) and specific sympathetic effects in target organs.

i. Atropine crosses the blood–brain barrier and is known to cause CNS stimulation, whereas synthetic agents, such as ipratropium, do not cross into brain tissue.

ii. In addition, the lungs have both cholinergic and adrenergic receptors that regulate bronchomotor tone. An anticholinergic agent may be considered in the management of a patient with asthma.

b. Indications. Include premedication for procedures or medications known to potentiate bradycardia, reduction of salivary secretions, bronchodilation (not as a first-line agent but as an adjunct), and symptom control while using a beta-blocker agent.

c. Nursing considerations

i. Pupil size and responsiveness are altered with atropine administration. This is important to note when a neurologic condition is being monitored. Fixed dilated pupils should not occur.

ii. Side effects may be bothersome to patients who are awake, including a fast heart rate, dry mouth, and CNS effects (delirium, agitation).

iii. Atropine crosses the blood–brain barrier and will cause CNS effects such as agitation.

3. Naloxone (Narcan)

a. Description. Naloxone is an opioid antagonist that has an affinity for opiate receptors, blocking them from binding to narcotics. Narcotics attached to the receptor are displaced. Naloxone is used to reverse the effects of morphine-like drugs. When given intravenously, the duration is 2 to 3 minutes.

b. Indications. Used for complete or partial reversal of opioid drug effects, including respiratory depression induced by natural or synthetic opioids, diagnosis and management of known or suspected acute opioid overdose, and for the prevention and treatment of opioid-induced pruritus.

c. Nursing considerations

i. Because of the quick onset of effect with naloxone, the patient may awaken abruptly and may be in pain or exhibit nausea and vomiting.

ii. Because of the short duration of effect with naloxone, there may be a recurrence of the narcotized state, necessitating repeated dosing or continuous infusion. Therefore, the patient requires constant monitoring because the effects of the morphine-like narcotics may last longer than the effects of naloxone.

4. Flumazenil (Romazicon)

a. Description. Romazicon is a reversal agent used for the benzodiazepines with a central mechanism of action.

b. Indications. Used for the reversal of benzodiazepine-related side effects, especially respiratory depression.

c. Nursing considerations

i. Patients should be monitored continuously with airway equipment at the bedside.

66ii. Use flumazenil with caution in patients with a history of seizures, massive overdoses, or concurrent use of tricyclic agents.

5. Other Agents. Nausea and pruritis frequently occur with many of the medications discussed in this section. See Table 2.9 for drug recommendations and dosing to manage these problems.

G. Agents That Affect Ventilation–Perfusion Matching

1. Nitric Oxide

a. Description. The underlying principle of inhaled nitric oxide (iNO) is its selectivity as a pulmonary vasodilator. iNO will relax only pulmonary smooth muscle adjacent to functioning alveoli. Atelectatic or fluid-filled units will not participate in iNO uptake. Therefore, if the pulmonary vasculature is constricted in atelectatic regions of the lung, pulmonary blood flow will remain minimal in these regions, reducing intrapulmonary shunt. This is in contrast to IV vasodilators such as nitroprusside or prostacycline. These drugs will relax pulmonary vasculature globally reducing PVR, but also increasing intrapulmonary right-to-left shunt (Lexicomp Online, 2016).

b. Indications. Approved for the treatment of hypoxic respiratory failure associated with clinical or echocardiographic evidence of PH used in conjunction with ventilator support and other agents to improve oxygenation and reduce the need for extracorporeal membrane oxygenation (ECMO; FDA approved for term and near-term [>34 weeks gestational age] neonates; Lexicomp Online, 2017).

c. Nursing considerations

i. Nitric oxide (NO) is an inhalational gas delivered through the ventilator circuitry at a flow of 10 to 80 parts per million (ppm). Doses above 20 ppm should not be used or be used with caution (off-label; Lexicomp Online, 2017).

ii. The half-life of iNO is extremely short, about 5 seconds. Once NO crosses the vascular endothelium, it is rapidly bound by hemoglobin-forming methemoglobin. The quantity of methemoglobin depends on iNO concentration and concurrent nitrate-based drug therapy. If the methemoglobin level is excessive, a reduction in iNO or other nitro-based vasodilators is warranted. Ultimately NO metabolites are excreted primarily by the kidneys as nitrates and nitrites. Methemoglobin levels should be noted on routine blood gas analysis.

iii. NO should not be abruptly discontinued if used for more than a short time because rebound effects can occur. To wean NO, titrate down in several steps, pausing several hours before reducing further; monitor for hypoxemia.

2. Surfactant Replacement Therapy

a. Description. Surfactant is produced by type II alveolar epithelial cells in the lung. Surfactant is composed mainly of lipids with only 5% to 10% proteins. Surfactant function includes preventing lung collapse during exhalation, lessening the WOB (VO₂), optimizing surface area for gas exchange and ventilation–perfusion matching, optimizing lung compliance, protecting the lung epithelium and facilitating clearance of foreign material, preventing capillary leakage of fluid into alveoli, and defending against microorganisms.

b. Indications. Exogenous surfactant administration is most commonly used for prophylaxis or treatment of preterm infants with RDS. Surfactant may be redosed in the first 48 hours of presentation. Surfactant is not used in pediatric acute respiratory distress syndrome (PARDS) and only used in neonates (Schnapf & Kirle, 2010)

c. Nursing considerations (Schnapf & Kirle, 2010)

i. Prophylactic surfactant is administered after a period of stabilization in the first 15 minutes of life.

ii. Surfactant should only be administered by intratracheal instillation using specialized techniques.

iii. The patient should be sedated and paralyzed to avoid a cough reflex during endotracheal administration of surfactant.

iv. Although repositioning the infant has been recommended, it is not necessary to move the infant into different positions during instillation as exogenous surfactant has remarkable spreading properties.

v. Side effects include the following: cyanosis, bradycardia, reflux of surfactant into the ETT, and airway obstruction. Therapy can rapidly affect oxygenation and lung compliance. Rales and moist breath sounds may occur transiently.

67vi. Do not suction airways for 1 hour after dosing unless substantial obstruction occurs.

3. Sildenafil (Lexicomp Online, 2016)

a. Description. Sildenafil inhibits phosphodiesterase type 5 (PDE-5) in smooth muscle of pulmonary vasculature where PDE-5 is responsible for the degradation of cyclic guanosine monophosphate (cGMP). Increased cGMP concentration results in pulmonary vasculature relaxation; vasodilation in the pulmonary bed and the systemic circulation (to a lesser degree) may occur.

b. Indications. PH

c. Nursing considerations

i. Typically administered orally although IV formulations exist.

ii. Patients should avoid grapefruit juice as it may increase serum levels/toxicity of sildenafil.

iii. Nursing should monitor heart rate, blood pressure, and oxygen saturation.

Tags: AACN Core Curriculum for Pediatric High Acuity Progressive

Feb 19, 2020 | Posted by admin in NURSING | Comments Off

Assisted Techniques
Chest physiotherapy (percussion, postural drainage, and vibration)	• Physical therapy techniques have been employed alone and in combination to facilitate airway clearance and to render cough more effective. • These maneuvers are established as the standard of care in patients with CF and in selected patients with other pulmonary conditions as a way to enhance the removal of tracheobronchial secretions. • However, chest physiotherapy is time-consuming, may require assistance of a therapist/caregiver, and may be uncomfortable or unpleasant.
Manually assisted cough	• Paradoxical outward motion of the abdomen during cough may occur in individuals with neuromuscular weakness or structural defects of the abdominal wall; this paradoxical motion contributes to cough inefficiency. Reducing this paradox either by manually compressing the lower thorax and abdomen or by binding the abdomen should theoretically improve cough efficiency. • The manually assisted cough maneuver consists of applying pressure with both hands to the upper abdomen following an inspiratory effort and glottic closure. • A disadvantage is that this requires the presence of a caregiver and is often not well tolerated and ineffective in patients with stiff chest walls, osteoporosis, who have undergone abdominal surgery, or who have intraabdominal catheters.
Unassisted Techniques
FET, also called huff-coughing	• This maneuver consists of one or two forced expirations without closure of the glottis starting at middle to low lung volume, followed by relaxed breathing. • Huff-coughing is as effective as directed cough in moving secretions proximally.
Autogenic drainage	• This technique uses controlled expiratory airflow during tidal breathing to mobilize secretions in the peripheral airways and move them centrally. • Three phases: (1) Unstick the mucus in the smaller airways by breathing at low lung volumes. (2) Collect the mucus from intermediate-sized airways by breathing at low to middle lung volumes. (3) Evacuate the mucus from the central airways by breathing at middle to high lung volumes. The individual then coughs or huffs to expectorate the mucus. • Technique can be performed in a seated position without the assistance of a caregiver. • Most commonly used in CF.
Respiratory muscle strength training	• Strengthening the inspiratory muscles may enhance cough effectiveness by increasing the volume of air inhaled during the inspiratory phase of the cough, whereas strengthening the muscles of exhalation may improve cough effectiveness by increasing intrathoracic pressure during the expiratory phase. 69 • In patients with neuromuscular weakness and impaired cough, expiratory muscle training is recommended to improve peak expiratory pressure, which may have a beneficial effect on cough.
Devices
PEP	• The administration of PEP from 5 to 20 cm H₂O delivered by facemask is believed to improve mucus clearance by either increasing gas pressure behind secretions through collateral ventilation or by preventing airway collapse during expiration.
Oscillatory devices (flutter, intrapulmonary percussive ventilation, high-frequency chest-wall oscillation)	• High-frequency oscillations can be applied either through the mouth or chest wall causing the airways to vibrate, thereby mobilizing secretions. These devices can be used with the patient seated or supine. • The “flutter” device is a plastic pipe with a mouthpiece at one end and a perforated cover at the other end. Within the device, a high-density stainless steel ball rests in a circular cone and creates a valve. Exhaling through the device creates oscillations in the airway, the frequency of which can be modulated by changing the inclination of the pipe. • The IPV uses small bursts of air at 200 to 300 cycles per minute along with entrained aerosols delivered through a mouthpiece. The putative mechanisms for efficacy include bronchodilation from increased airway pressure, increased airway humidification, and cough stimulation. • The method of high-frequency oscillation applied to the chest wall has been referred to as either high-frequency chest compression or high-frequency chest-wall oscillation. These devices are designed to oscillate gas in the airway.
Mechanical insufflation–exsufflation	• Modalities directed at increasing the volume inhaled during the inspiratory phase of cough also increase cough effectiveness. The inability of patients with respiratory muscle weakness to achieve high lung volumes contributes to cough ineffectiveness. Cough efficiency can be further enhanced when the initial inspiration is followed by the application of negative pressure to the airway opening for a period of 1–3 sec. Peak cough flows can be increased.
Electrical stimulation of the expiratory muscles	• Electrical stimulation of the abdominal muscles can also increase expiratory pressures and has the advantage of not requiring the presence of a caregiver. Coughs produced by electrical stimulation are associated with expiratory flows equal to the manually assisted coughs.

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