Physiologic and Behavioral Adaptations of the Newborn



Physiologic and Behavioral Adaptations of the Newborn


Shannon E. Perry




Key Terms and Definitions




















Web Resources


Additional related content can be found on the companion website at image


evolve.elsevier.com/Lowdermilk/Maternity/




T he neonatal period includes the time from birth through day 28 of life. By term gestation, the various anatomic and physiologic systems of the fetus have reached a level of development and functioning that permits a separate existence from the mother. At birth the newborn infant exhibits behavioral competencies and a readiness for social interaction. These adaptations set the stage for future growth and development.



Transition to Extrauterine Life image


Newborns undergo phases of instability during the first 6 to 8 hours after birth. These phases are collectively called the transition period between intrauterine and extrauterine existence. The first phase of the transition period lasts up to 30 minutes after birth and is called the first period of reactivity. The newborn’s heart rate increases rapidly to 160 to 180 beats/minute but gradually falls after 30 minutes or so to a baseline rate of between 100 and 120 beats/minute. Respirations are irregular, with a rate between 60 and 80 breaths/minute. Fine crackles may be present on auscultation; audible grunting, nasal flaring, and retractions of the chest also may be noted, but these should cease within the first hour of birth. The infant is alert and may have spontaneous startles, tremors, crying, and movement of the head from side to side. Bowel sounds are audible, and meconium may be passed.


After the first period of reactivity the newborn either sleeps or has a marked decrease in motor activity. This period of unresponsiveness, often accompanied by sleep, lasts from 60 to 100 minutes and is followed by a second period of reactivity.


The second period of reactivity occurs roughly between 4 and 8 hours after birth and lasts from 10 minutes to several hours. Brief periods of tachycardia and tachypnea occur, associated with increased muscle tone, skin color, and mucous production. Meconium is commonly passed at this time. Most healthy newborns experience this transition regardless of gestational age or type of birth; extremely and very preterm infants do not because of physiologic immaturity.



Physiologic Adaptations image


Respiratory System


With the cutting of the umbilical cord the infant undergoes rapid and complex physiologic changes. The most critical and immediate adjustment a newborn makes at birth is the establishment of respirations. With a vaginal birth some lung fluid is squeezed from the newborn’s trachea and lungs; in infants who are born by cesarean birth some lung fluid may be retained within the alveoli. With the first breath of air the newborn begins a sequence of cardiopulmonary changes (Table 16-1).



TABLE 16-1


Characteristics of the Respiratory System of the Neonate


































CHARACTERISTIC EFFECT ON FUNCTION
Decreased lung elastic tissue and recoil Decreased lung compliance requiring higher pressures and more work to expand; increased risk of atelectasis
Reduced diaphragm movement and maximal force potential Less effective respiratory movement; difficulty generating negative intrathoracic pressures; risk of atelectasis
Tendency to nose breathe; altered position of larynx and epiglottis Enhanced ability to synchronize swallowing and breathing; risk of airway obstruction; possibly more difficult to intubate
Small compliant airway passages with higher airway resistance; immature reflexes Risk of airway obstruction and apnea
Increased pulmonary vascular resistance with sensitive pulmonary arterioles Risk of ductal shunting and hypoxemia with events such as hypoxia, acidosis, hypothermia, hypoglycemia, and hypercarbia
Increased oxygen consumption Increased respiratory rate and work of breathing; risk of hypoxia
Increased intrapulmonary right-left shunting Increased risk of atelectasis with wasted ventilation; lower PCO2
Immaturity of pulmonary surfactant system in immature infants Increased risk of atelectasis and respiratory distress syndrome; increased work of breathing
Immature respiratory control Irregular respirations with periodic breathing; risk of apnea; inability to rapidly alter depth of respirations

PCO2: Partial pressure of carbon dioxide.


From Blackburn, S. (2007). Maternal, fetal, & neonatal physiology: A clinical perspective (3rd ed.). St. Louis: Saunders.


Initial breathing is probably the result of a reflex triggered by pressure changes, exposure to cool air temperature, noise, light, and other sensations related to the birth process. In addition, the chemoreceptors in the aorta and carotid bodies initiate neurologic reflexes when arterial oxygen pressure (PO2) falls, arterial carbon dioxide pressure (PCO2) rises, and arterial pH falls. In most cases an exaggerated respiratory reaction follows within 1 minute of birth, and the infant takes a first gasping breath and cries.


Once respirations are established, breaths are shallow and irregular, ranging from 30 to 60 breaths/minute, with periods of periodic breathing that include pauses in respirations lasting less than 20 seconds. These episodes of periodic breathing occur most often during the active (rapid eye movement [REM]) sleep cycle and decrease in frequency and duration with age. Apneic periods longer than 20 seconds are an indication of a pathologic process and should be thoroughly evaluated.



Signs of Respiratory Distress


Most term infants breathe spontaneously and continue to have normal respirations. Signs of respiratory distress may include nasal flaring, intercostal or subcostal retractions (in-drawing of tissue between the ribs or below the rib cage), or grunting with respirations. Suprasternal or subclavicular retractions with stridor or gasping most often represent an upper airway obstruction. Seesaw or paradoxical respirations (exaggerated rise in abdomen, with respiration, as the chest falls) instead of abdominal respirations are abnormal and should be reported. A respiratory rate of less than 30 or greater than 60 breaths/minute with the infant at rest must be thoroughly evaluated. The respiratory rate of the infant can be slowed, depressed, or absent due to the effects of analgesics or anesthetics administered to the mother during labor and birth. Apneic episodes can be related to several events (rapid increase in body temperature; hypothermia, hypoglycemia, and sepsis) that require thorough evaluation. Tachypnea may result from inadequate clearance of lung fluid, or it may be an indication of newborn respiratory distress syndrome.



Maintaining adequate oxygen supply


During the first hour of life the pulmonary lymphatics continue to remove large amounts of fluid. Removal of fluid is also a result of the pressure gradient from alveoli to interstitial tissue to blood capillary. Reduced vascular resistance accommodates this flow of lung fluid. Retention of lung fluid may interfere with the infant’s ability to maintain adequate oxygenation, especially if other factors that compromise respirations are present (meconium aspiration, congenital diaphragmatic hernia, esophageal atresia with fistula, choanal atresia, congenital cardiac defect, immature alveoli [absent or decreased]).


The term newborn’s chest circumference is approximately 30 to 33 cm at birth. Auscultation of the chest of a newborn reveals loud, clear breath sounds that seem very near because the infant has little chest wall musculature. The ribs of the infant articulate with the spine at a horizontal rather than a downward slope; consequently, the rib cage cannot expand with inspiration as readily as that of an adult. Because neonatal respiratory function is largely a matter of diaphragmatic contraction, abdominal breathing is characteristic of newborns. That is, the newborn infant’s chest and abdomen rise simultaneously with inspiration, but because of the large size of the abdomen, chest movement is not as visible.


The outer walls of the alveoli are lined with surfactant, a protein manufactured in type II cells of the lungs. Lung expansion is largely dependent on chest wall contraction and adequate presence and secretion of surfactant. Surfactant lowers surface tension, therefore reducing the pressure required to keep the alveoli open with inspiration, and prevents total alveolar collapse on exhalation, thereby maintaining alveolar stability. With absent or decreased surfactant, more pressure must be generated for inspiration, which may soon tire or exhaust preterm or sick term infants. Surfactant may be compared with soapy water on the inside of a balloon. Sometimes the sides of an uninflated balloon stick together and cannot expand. If some soapy water is poured into the balloon, the surfaces are slippery and prevent the sides from sticking; this allows the balloon to expand.



Cardiovascular System


The cardiovascular system changes significantly after birth. The infant’s first breaths, combined with increased alveolar capillary distention, inflate the lungs and reduce pulmonary vascular resistance to the pulmonary blood flow from the pulmonary arteries. Pulmonary artery pressure drops, and pressure in the right atrium declines. Increased pulmonary blood flow to the left side of the heart increases pressure in the left atrium, which causes a functional closure of the foramen ovale. During the first few days of life, crying may reverse the flow through the foramen ovale temporarily and lead to mild cyanosis (Table 16-2).



TABLE 16-2


Cardiovascular Changes at Birth









































PRENATAL STATUS POSTBIRTH STATUS ASSOCIATED FACTORS
PRIMARY CHANGES
Pulmonary circulation: high pulmonary vascular resistance, increased pressure in right ventricle and pulmonary arteries Low pulmonary vascular resistance; decreased pressure in right atrium, ventricle, and pulmonary arteries Expansion of collapsed fetal lung with air
Systemic circulation: low pressures in left atrium, ventricle, and aorta High systemic vascular resistance; increased pressure in left atrium, ventricle, and aorta Loss of placental blood flow
SECONDARY CHANGES
Umbilical arteries: patent, carrying of blood from hypogastric arteries to placenta Functionally closed at birth; obliteration by fibrous proliferation possibly taking 2-3 mo, distal portions becoming lateral vesicoumbilical ligaments, proximal portions remaining open as superior vesicle arteries Closure preceding that of umbilical vein, probably accomplished by smooth muscle contraction in response to thermal and mechanical stimuli and alteration in oxygen tension, mechanically severed with cord at birth
Umbilical vein: patent, carrying of blood from placenta to ductus venosus and liver Closed, becoming ligamentum teres hepatis after obliteration Closure shortly after umbilical arteries, hence blood from placenta possibly entering neonate for short period after birth, mechanically severed with cord at birth
Ductus venosus: patent, connection of umbilical vein to inferior vena cava Closed, becoming ligamentum venosum after obliteration Loss of blood flow from umbilical vein
Ductus arteriosus: patent, shunting of blood from pulmonary artery to descending aorta Functionally closed almost immediately after birth, anatomic obliteration of lumen by fibrous proliferation requiring 1-3 mo, becoming ligamentum arteriosum Increased oxygen content of blood in ductus arteriosus creating vasospasm of its muscular wall
High systemic resistance increasing aortic pressure; low pulmonary resistance reducing pulmonary arterial pressure
Foramen ovale: formation of a valve opening that allows blood to flow directly to left atrium (shunting of blood from right to left atrium) Functionally closed at birth, constant apposition gradually leading to fusion and permanent closure within a few months or years in majority of persons Increased pressure in left atrium and decreased pressure in right atrium causing closure of valve over foramen


image


In utero, fetal PO2 is 27 mm Hg. After birth, when the PO2 level in the arterial blood approximates 50 mm Hg, the ductus arteriosus constricts in response to increased oxygenation. Circulating levels of the hormone prostaglandin E (PGE2) also have an important role in closure of the ductus arteriosus. Later, the ductus arteriosus closes completely and becomes a ligament. With the clamping of the cord, the umbilical arteries, umbilical vein, and ductus venosus close and are converted into ligaments. The hypogastric arteries also occlude and become ligaments.



Heart rate and sounds


The heart rate averages 100 to 160 beats/minute, with variations noted during sleeping and waking states. Shortly after the first cry the infant’s heart rate may accelerate as high as 175 to 180 beats/minute. The range of the heart rate in the term infant is approximately 85 to 90 beats/minute during deep sleep and up to 170 or more beats/minute while the infant is awake. A heart rate of 180 beats/minute is not unusual when the infant cries. A heart rate that is either consistently high (>170 beats/min) or low (<80 beats/min) with the newborn at rest should be reevaluated within an hour or when the activity of the infant changes.


The apical impulse (point of maximal impulse [PMI]) in the newborn is located at the fourth intercostal space and to the left of the midclavicular line. The PMI is often visible and easily palpable because of the thin chest wall; this is also called precordial activity.


Apical pulse rates should be assessed on all infants. Auscultation should be for a full minute, preferably when the infant is asleep. An irregular heart rate is not uncommon in the first few hours of life. After this time an irregular heart rate not attributed to changes in activity or respiratory pattern should be further evaluated.


Heart sounds during the neonatal period are of higher pitch, shorter duration, and greater intensity than those during adult life. The first sound (S1) is typically louder and duller than the second sound (S2), which is sharp. The third and fourth heart sounds are not auscultated in newborns. Most heart murmurs heard during the first few days of life have no pathologic significance, and more than one half of the murmurs disappear by 6 months. However, the presence of a murmur and accompanying signs such as poor feeding, apnea, cyanosis, or pallor are considered abnormal and should be further investigated.



Blood pressure


The newborn infant’s average systolic blood pressure (BP) is 60 to 80 mm Hg, and the average diastolic pressure is 40 to 50 mm Hg. The BP increases by the second day of life, with minor variations noted during the first month of life. A drop in systolic BP (approximately 15 mm Hg) in the first hour of life is common. Crying and movement usually cause increases in the systolic pressure. The measurement of BP is best accomplished with an oscillometric device while the infant is at rest. A correctly sized cuff must be used for accurate measurement of an infant’s BP.


Unless a specific indication exists, BP is not usually measured in the newborn on a routine basis except as a baseline. The practice of obtaining four extremity BPs in the early newborn period to detect coarctation of the aorta (COA) has been recently questioned (Razmus & Lewis, 2006). This is based on evidence that COA defects do not occur in the immediate postbirth period but more typically at approximately 12 to 14 days of age, a time when the ductus arteriosus closes (Taylor, 2005).



Blood volume


The blood volume of the newborn is approximately 80 to 85 ml/kg of body weight. Immediately after birth the total blood volume averages 300 ml, but this volume can increase by as much as 100 ml, depending on the length of time before the cord is clamped and cut. The preterm infant has a relatively greater blood volume than the term newborn because the preterm infant has a proportionately greater plasma volume, not a greater red blood cell (RBC) mass.


Early or late clamping of the umbilical cord changes the circulatory dynamics of the newborn. Late clamping expands the blood volume from the so-called placental transfusion of blood to the newborn. Delayed cord clamping (≥2 minutes after birth) has been reported to result in polycythemia with subsequent clinical signs of hyperviscosity (hematocrit ≥65%, plethoric or ruddy red appearance, sluggish circulation leading to possible emboli in the microvasculature and organ damage, respiratory distress, and possibly hyperbilirubinemia as a result of red cell breakdown) (Armentrout & Huseby, 2003). However, recent data showed delayed cord clamping (no longer than 2 minutes after birth) in full-term neonates was found to be beneficial in improving hematocrit and iron status and in decreasing anemia; such benefits were observed over ages 2 to 6 months. Polycythemia occurred with delayed clamping but was not harmful (Hutton & Hassan, 2007).



Hematopoietic System


The hematopoietic system of the newborn exhibits certain variations from that of the adult. Levels of RBCs and leukocytes differ, but platelet levels are relatively the same.



Red blood cells and hemoglobin


At birth the average levels of RBCs and hemoglobin (fetal hemoglobin is predominant) are higher than those in the adult. Cord blood of the term newborn may have a hemoglobin concentration of 14 to 24 g/dl (mean, 17 g/dl). The hematocrit ranges from 44% to 64% (mean, 55%). The RBC count is correspondingly elevated, ranging from 4.8 to 7.1 million/mm3 (mean, 5.14 million/mm3). By the end of the first month, these values fall and reach the average levels of 11 to 17 g/dl and 4.2 to 5.2 million/mm3, respectively.


The blood values may be affected by delayed clamping of the cord, which results in a rise in hemoglobin, RBCs, and hematocrit. The source of the sample is a significant factor because capillary blood yields higher values than venous blood. The timing of blood sampling is also significant; the slight rise in RBCs after birth is followed by a substantial drop. At birth the infant’s blood contains an average of 70% fetal hemoglobin, but because of the shorter life span of the cells containing fetal hemoglobin, the percentage falls to 55% by 5 weeks and to 5% by 20 weeks. Iron stores generally are sufficient to sustain normal RBC production for 4 to 5 months in the term infant, at which time a physiologic anemia that is usually transient can occur.



Leukocytes


Leukocytosis, with a white blood cell (WBC) count of approximately 18,000 cells/mm3 (range, 9000 to 30,000 cells/mm3), is normal at birth. The number of WBCs increases to 23,000 to 24,000 cells/mm3 during the first day after birth. This initial high WBC count of the newborn decreases rapidly, and a resting level of 11,500 cells/mm3 is normally maintained during the neonatal period. Serious infection is not well tolerated by the newborn; leukocytes are slow to recognize foreign protein and to localize and fight infection early in life. Sepsis may be accompanied by a concomitant rise in WBCs (neutrophilia); however, some infants may exhibit clinical signs of sepsis without a significant elevation in WBCs. In addition, events other than infection may cause neutrophilia in the newborn. These events include prolonged crying, maternal hypertension, asymptomatic hypoglycemia, hemolytic disease, meconium aspiration syndrome, labor induction with oxytocin, surgery, difficult labor, high altitude, and maternal fever.





Thermogenic System


Next to establishing respirations and adequate circulation, heat regulation is most critical to the newborn’s survival. Thermoregulation is the maintenance of balance between heat loss and heat production. Newborns attempt to stabilize their core body temperatures within a narrow range. Hypothermia from excessive heat loss is a common and dangerous problem in neonates. The newborn infant’s ability to produce heat (thermogenesis) often approaches that of the adult; however, the tendency toward rapid heat loss in a cold environment is increased in the newborn and poses a hazard.



Thermogenesis


The shivering mechanism of heat production is rarely operable in the newborn. Nonshivering thermogenesis is accomplished primarily by metabolism of brown fat, which is unique to the newborn, and secondarily by increased metabolic activity in the brain, heart, and liver. Brown fat is located in superficial deposits in the interscapular region and axillae, as well as in deep deposits at the thoracic inlet, along the vertebral column, and around the kidneys. Brown fat has a richer vascular and nerve supply than ordinary fat. Heat produced by intense lipid metabolic activity in brown fat can warm the newborn by increasing heat production as much as 100%. Reserves of brown fat, usually present for several weeks after birth, are rapidly depleted with cold stress. The amount of brown fat reserve increases with the weeks of gestation. A full-term newborn has greater stores than a preterm infant.



Heat loss


Heat loss in the newborn occurs by four modes:



• Convection is the flow of heat from the body surface to cooler ambient air. Because of heat loss by convection the ambient temperature in the nursery is kept at approximately 24° C, and newborns in open bassinets are wrapped to protect them from the cold.


• Radiation is the loss of heat from the body surface to a cooler solid surface not in direct contact but in relative proximity. To prevent this type of loss, nursery cribs and examining tables are placed away from outside windows, and care is taken to avoid direct air drafts.


• Evaporation is the loss of heat that occurs when a liquid is converted to a vapor. In the newborn, heat loss by evaporation occurs as a result of vaporization of moisture from the skin. This heat loss can be intensified by failure to dry the newborn directly after birth or by drying the infant too slowly after a bath. The less mature the newborn is, the more severe the evaporative heat loss will be. Evaporative heat loss, as a component of insensible water loss, is the most significant cause of heat loss in the first few days of life.


• Conduction is the loss of heat from the body surface to cooler surfaces in direct contact. When admitted to the nursery the newborn is placed in a warmed crib to minimize heat loss. The scales used for weighing the newborn should have a protective cover to minimize conductive heat losses as well.


Loss of heat must be controlled to protect the infant. Control of such modes of heat loss is the basis of caregiving policies and techniques. One method for promoting maternal-newborn interaction is to place the naked healthy newborn next to the mother’s skin and cover both with a blanket. This skin-to-skin contact enhances newborn temperature control and interaction (Fig. 16-1).




Temperature regulation


Anatomic and physiologic differences among the newborn, child, and adult are notable. The newborn’s ability to produce heat is initially less than that of an adult. Newborns have larger body surface-body weight (mass) ratios than children and adults. The flexed position of the newborn helps guard against heat loss because it diminishes the amount of body surface exposed to the environment. Infants can also reduce the loss of internal heat through the body surface by constricting peripheral blood vessels.


Cold stress imposes metabolic and physiologic demands on all infants, regardless of gestational age and condition. The respiratory rate increases in response to the increased need for oxygen. In the cold-stressed infant, oxygen consumption and energy are diverted from maintaining normal brain and cardiac function and growth to thermogenesis for survival. If the infant cannot maintain an adequate oxygen tension, vasoconstriction follows and jeopardizes pulmonary perfusion. As a consequence, the PO2 is decreased, and the blood pH drops. These changes may prompt a transient respiratory distress or may aggravate existing respiratory distress syndrome. Moreover, decreased pulmonary perfusion and oxygen tension may maintain or reopen the right-to-left shunt across the patent ductus arteriosus.


The basal metabolic rate increases with cold stress (Fig. 16-2). If cold stress is protracted, anaerobic glycolysis occurs, resulting in increased production of acids. Metabolic acidosis develops, and if a defect in respiratory function is present, respiratory acidosis also develops. Excessive fatty acids may displace the bilirubin from the albumin-binding sites and exacerbate hyperbilirubinemia.



Hypoglycemia is another metabolic consequence of cold stress. The process of anaerobic glycolysis uses approximately three to four times the amount of blood glucose, thereby depleting existing stores. If the infant is sufficiently stressed and low glucose stores are not replaced, hypoglycemia, which can be asymptomatic in the newborn, may develop.


Hyperthermia develops more rapidly in the newborn than in the adult because of the decreased ability to increase evaporative skin water losses. Although newborn infants have six times as many sweat glands per unit area as adults, in most newborns these glands do not function sufficiently to allow the infant to sweat. Serious overheating of the newborn can cause cerebral damage from dehydration or heat stroke and death.



Renal System


At term gestation the kidneys occupy a large portion of the posterior abdominal wall. The bladder lies close to the anterior abdominal wall and is an abdominal organ and a pelvic organ. In the newborn almost all palpable masses in the abdomen are renal in origin.


A small quantity (approximately 40 ml) of urine is usually present in the bladder of a full-term infant at birth. The frequency of voiding varies from two to six times per day during the first and second days of life and from 5 to 25 times per day thereafter. Approximately six to eight voidings per day of pale straw-colored urine are indicative of adequate fluid intake after the first 3-4 days. Generally, term infants void 15 to 60 ml of urine/kg/day.


Full-term infants have limited capacity to concentrate urine; therefore the specific gravity of the urine may range from 1.001 to 1.020. The ability to concentrate urine fully is attained by approximately 3 months of age. After the first voiding the infant’s urine may appear cloudy (because of mucous content) and have a much higher specific gravity. This level decreases as fluid intake increases. Normal urine during early infancy is usually straw colored and almost odorless. During the first week after birth, urine contains an abundance of uric acid crystals that may appear as pink or orange stains (“brick dust”) on the diaper. If this occurs after the first week, it can be an indication of insufficient intake.


It is common for newborns to lose 5% to 7% of their birth weight during the first 3 to 5 days of life. This is the result of fluid loss through urine, feces, and lungs, as well as an increased metabolic rate and limited fluid intake. If the mother is breastfeeding and her milk supply has not yet transitioned to the higher volume mature milk by the third or fourth day, the neonate is somewhat protected from dehydration by the increased extracellular fluid volume that is present at birth. Weight loss in excess of 7% of birth weight can indicate feeding problems, especially in the breastfeeding infant. This warrants further assessment of feedings. If the weight loss reaches 10% of birth weight during the first week of life, there is cause for concern. The neonate should regain the birth weight within 10 to 14 days, depending on the feeding method (breast or bottle).


Because renal thresholds are low in the infant, bicarbonate concentration and buffering capacity are decreased. This reduction may lead to acidosis and electrolyte imbalance.



Fluid and electrolyte balance


Approximately 40% of the body weight of the newborn is extracellular fluid. Each day the newborn takes in and excretes roughly 600 to 700 ml of fluid, which is 20% of the total body fluid or 50% of the extracellular fluid. The glomerular filtration rate of a newborn is approximately 30% to 50% that of the adult. This lower filtration rate results in a decreased ability to remove nitrogenous and other waste products from the blood. However, the newborn’s ingested protein is almost totally metabolized for growth.


Sodium reabsorption is decreased as a result of a lowered sodium- or potassium-activated adenosine triphosphatase activity. The decreased ability to excrete excessive sodium results in hypotonic urine compared with plasma, leading to a higher concentration of sodium, phosphates, chloride, and organic acids and a lower concentration of bicarbonate ions. The infant has a higher renal threshold for glucose than adults.



Gastrointestinal System


The term newborn is capable of swallowing, digesting, metabolizing, and absorbing proteins and simple carbohydrates and emulsifying fats. With the exception of pancreatic amylase the characteristic enzymes and digestive juices are present even in low-birth-weight neonates.


In the adequately hydrated infant the mucous membrane of the mouth is moist and pink. The hard and soft palates are intact. The presence of moderate to large amounts of mucus is common in the first few hours after birth. Small whitish areas (Epstein pearls) may be found on the gum margins and at the juncture of the hard and soft palate. The cheeks are full because of well-developed sucking pads. These pads, like the labial tubercles (sucking calluses) on the upper lip, disappear around the age of 12 months, when the sucking period is over.


Even though sucking motions in utero have been recorded by ultrasound, these motions are not coordinated with swallowing in any infant born before 32 to 33 weeks of gestation. Sucking behavior is influenced by neuromuscular maturity, maternal medications received during labor and birth, and the type of initial feeding.


A special mechanism present in healthy term newborns coordinates the breathing, sucking, and swallowing reflexes necessary for oral feeding. Sucking in the newborn takes place in small bursts of three or four and up to eight to ten sucks at a time, with a brief pause in between bursts. The infant is unable to move food from the lips to the pharynx; therefore placing the nipple (breast or bottle) well inside the baby’s mouth is necessary. Peristaltic activity in the esophagus is uncoordinated in the first few days of life. It quickly becomes a coordinated pattern in healthy full-infants and they swallow easily.


Teeth begin developing in utero, with enamel formation continuing until approximately age 10 years. Tooth development is influenced by neonatal or infant illnesses, medications, and illnesses of or medications taken by the mother during pregnancy. The fluoride level in the water supply also influences tooth development. Occasionally an infant may be born with one or more teeth.


Bacteria are not present in the infant’s gastrointestinal tract at birth. Soon after birth, oral and anal orifices permit entry of bacteria and air. Generally, the highest bacterial concentration is found in the lower portion of the intestine, particularly in the large intestine. Normal colonic bacteria are established within the first week after birth, and normal intestinal flora help synthesize vitamin K, folate, and biotin. Bowel sounds can usually be heard shortly after birth.


The capacity of the stomach varies from 30 to 90 ml, depending on the size of the infant. Emptying time for the stomach is highly variable. Several factors, such as time and volume of feedings or type and temperature of food, may affect the emptying time. The cardiac sphincter and nervous control of the stomach are immature, thus some regurgitation may occur. Regurgitation during the first day or two of life can be decreased by avoiding overfeeding, by burping the infant, and by positioning the infant with the head slightly elevated.



Digestion


The infant’s ability to digest carbohydrates, fats, and proteins is regulated by the presence of certain enzymes. Most of these enzymes are functional at birth. One exception is amylase, produced by the salivary glands after approximately 3 months and by the pancreas at approximately 6 months of age. This enzyme is necessary to convert starch into maltose and occurs in high amounts in colostrum. The other exception is lipase, also secreted by the pancreas; it is necessary for the digestion of fat. Therefore the normal newborn is capable of digesting simple carbohydrates and proteins but has a limited ability to digest fats.


Further digestion and absorption of nutrients occur in the small intestine in the presence of pancreatic secretions, secretions from the liver through the common bile duct, and secretions from the duodenal portion of the small intestine.



Stools


At birth the lower intestine is filled with meconium. Meconium is formed during fetal life from the amniotic fluid and its constituents, intestinal secretions (including bilirubin), and cells (shed from the mucosa). Meconium is greenish black and viscous and contains occult blood. The first meconium passed is usually sterile, but within hours, all meconium passed contains bacteria. The majority of healthy term infants pass meconium within the first 12 to 24 hours of life, and almost all do so by 48 hours (Blackburn, 2007). The number of stools passed varies during the first week, being most numerous between the third and sixth days. Newborns fed early pass stools sooner. Progressive changes in the stooling pattern indicate a properly functioning gastrointestinal tract (Box 16-1).




Hepatic System


The liver and gallbladder are formed by the fourth week of gestation. In the newborn the liver can be palpated approximately 1 cm below the right costal margin because it is enlarged and occupies approximately 40% of the abdominal cavity. The infant’s liver plays an important role in iron storage, carbohydrate metabolism, conjugation of bilirubin, and coagulation.





Carbohydrate metabolism

At birth the newborn is cut off from its maternal glucose supply and, as a result, has an initial decrease in serum glucose levels. The newborn’s increased energy needs, decreased hepatic release of glucose from glycogen stores, increased RBC volume, and increased brain size may initially contribute to the rapid depletion of stored glycogen within the first 24 hours after birth. In most healthy term newborns, blood glucose levels stabilize at 50 to 60 mg/dl during the first several hours after birth; by the third day of life the blood glucose levels should be approximately 60 to 70 mg/dl. The initiation of feedings assists in the stabilization of the newborn’s blood glucose levels. Colostrum contains high amounts of glucose thus also assisting in the stabilization of blood glucose levels in breastfed neonates (colostrum is higher in protein, but lower in glucose, than mature milk) (see Evidence-Based Practice box in Chapter 17).



Jaundice

Jaundice is the manifestation of the pigment bilirubin in the tissues of the body. Jaundice does not usually appear until the bilirubin level reaches 5 mg/dl. Any visible jaundice within the first 24 hours of life or persistence of jaundice beyond 7 to 10 days requires further investigation into the cause as this represents an underlying pathologic process (Fig. 16-3). See Chapter 17 for a further discussion of bilirubin metabolism and hyperbilirubinemia.






Immune System


The cells that provide the infant with immunity are developed early in fetal life; however, they are not activated for weeks to months after birth. For the first 3 months of life the healthy term infant is somewhat protected by passive immunity received from the mother; however, this status is dependent on the mother’s previous exposure to antigens and her immunologic response. The membrane-protective immunoglobulin A (IgA) is missing from the respiratory and urinary tracts, and unless the newborn is breastfed, is also absent from the gastrointestinal tract. The infant begins to synthesize IgG, and approximately 40% of adult levels are reached by age 1 year. Significant amounts of IgM are produced at birth, and adult levels are reached by 9 months of age. The production of IgA, IgD, and IgE is much more gradual, and maximal levels are not attained until early childhood. The infant who is breastfed receives significant passive immunity through the colostrum and breast milk.



Integumentary System


All skin structures are present at birth. The epidermis and dermis are loosely bound and extremely thin. Vernix caseosa (a cheeselike, whitish substance) is fused with the epidermis and serves as a protective covering. The infant’s skin is very sensitive and can be easily damaged. The term infant has an erythematous (red) skin color for a few hours after birth, after which it fades to its normal color. The skin often appears blotchy or mottled, especially over the extremities. The hands and feet appear slightly cyanotic (acrocyanosis), which is caused by vasomotor instability and capillary stasis. Acrocyanosis is normal and appears intermittently over the first 7 to 10 days, especially with exposure to cold.


The healthy term newborn has a plump appearance because of large amounts of subcutaneous tissue and extracellular water content. Fine lanugo hair may be noted over the face, shoulders, and back. Edema of the face and ecchymosis (bruising) or petechiae may be present as a result of face presentation, forceps-assisted birth, or vacuum extraction (see Fig. 17-6).


Creases can be found on the palms of the hands. The simian line, a single palmar crease, is often found in Asian infants or in infants with Down syndrome.



Caput succedaneum


Caput succedaneum is a generalized, easily identifiable edematous area of the scalp, most commonly found on the occiput (Fig. 16-4, A). The sustained pressure of the presenting vertex against the cervix results in compression of local vessels, thereby slowing venous return. The slower venous return causes an increase in tissue fluids within the skin of the scalp, and an edematous swelling develops. This edematous swelling, present at birth, extends across suture lines of the skull and disappears spontaneously within 3 to 4 days. Infants who are born with the assistance of vacuum extraction usually have a caput in the area where the cup was applied.





Cephalhematoma


Cephalhematoma is a collection of blood between a skull bone and its periosteum; therefore a cephalhematoma does not cross a cranial suture line (Fig. 16-4, B). Caput succedaneum and cephalhematoma often occur simultaneously.


Bleeding may occur with spontaneous birth from pressure against the maternal bony pelvis. Low forceps birth and difficult forceps rotation and extraction may also cause bleeding. This soft, fluctuating, irreducible fullness does not pulsate or bulge when the infant cries. It appears several hours or the day after birth and may not become apparent until a caput succedaneum is absorbed. A cephalhematoma is usually largest on the second or third day, by which time the bleeding stops. The fullness of a cephalhematoma spontaneously resolves in 3 to 6 weeks. It is not aspirated because infection may develop if the skin is punctured. As the hematoma resolves, hemolysis of RBCs occurs, and jaundice may result. Hyperbilirubinemia and jaundice may occur after the newborn is discharged home.



Subgaleal hemorrhage


Subgaleal hemorrhage is bleeding into the subgaleal compartment (Fig. 16-4, C). The subgaleal compartment is a potential space that contains loosely arranged connective tissue; it is located beneath the galea aponeurosis, the tendinous sheath that connects the frontal and occipital muscles and forms the inner surface of the scalp. The injury occurs as a result of forces that compress and then drag the head through the pelvic outlet (Paige & Moe, 2006). Researchers have reported concern regarding the increased use of the vacuum extractor at birth and an association with cases of subgaleal hemorrhage, neonatal morbidity, and deaths (Boo, Foong, Mahdy, Yong, & Jaafar, 2005: Uchil & Arulkumaran, 2003). The bleeding extends beyond bone, often posteriorly into the neck, and continues after birth, with the potential for serious complications such as anemia or hypovolemic shock.


Early detection of the hemorrhage is vital; serial head circumference measurements and inspection of the back of the neck for increasing edema and a firm mass are essential. A boggy scalp, pallor, tachycardia, and increasing head circumference may also be early signs of a subgaleal hemorrhage (Doumouchtsis & Arulkumaran, 2006). Computed tomography or magnetic resonance imaging is useful in confirming the diagnosis. Replacement of lost blood and clotting factors is required in acute cases of hemorrhage. Another possible early sign of subgaleal hemorrhage is a forward and lateral positioning of the infant’s ears because the hematoma extends posteriorly. Monitoring the infant for changes in level of consciousness and a decrease in the hematocrit are also key to early recognition and management. An increase in serum bilirubin levels may be seen as a result of the breakdown of blood cells within the hematoma.






Nevi


Telangiectatic nevi, known as “stork bites,” are pink and easily blanched (Fig. 16-6, A). They appear on the upper eyelids, nose, upper lip, lower occipital area, and nape of the neck. They have no clinical significance and fade by the second year of life.



The nevus vasculosus is a common type of capillary hemangioma. It consists of dilated, newly formed capillaries occupying the entire dermal and subdermal layers, with associated connective tissue hypertrophy. The typical lesion is a raised, sharply demarcated, bright- or dark-red, rough-surfaced swelling. As the infant grows the hemangioma may proliferate and become more vascular, thereby often being called a strawberry hemangioma. Lesions are usually single but may be multiple, with 75% occurring on the head. These lesions can remain until the child is of school age or sometimes even longer but can be removed successfully with pulsed dye laser therapy, interferon therapy, and prednisone administration. In some cases, subcutaneous injections of interferon alfa-2a or interferon alfa-2b may be required if prednisone therapy and the pulsed dye laser fail to control a problematic hemangioma.


A port-wine stain, or nevus flammeus, is usually observed at birth and is composed of a plexus of newly formed capillaries in the papillary layer of the corium. It is red to purple; varies in size, shape, and location; and is not elevated. True port-wine stains do not blanch on pressure or disappear. They are most commonly found on the face and neck.

Oct 8, 2016 | Posted by in NURSING | Comments Off on Physiologic and Behavioral Adaptations of the Newborn
Premium Wordpress Themes by UFO Themes