Respiratory Support Modalities
Oxygen Delivery Devices
Donald Artes/Cathy Haut
Discussion
In order to provide supplemental oxygenation for a child with hypoxia or ineffective ventilation, a variety of oxygen delivery devices are available for use.
Indications include pathophysiologic hypoxemia, ineffective oxygenation related to neurologic illness or trauma, postanesthesia, and conditions resulting in myocardial ischemia.
Definition
An oxygen delivery device provides supplemental oxygen through the upper airways to the lungs via either low-flow or high-flow systems.
Types
Low-flow devices: Provide oxygen at flow rates that are less than the patient’s inspiratory demand.
Nasal cannula: Delivers oxygen concentrations of approximately 24% to 44% at flow rates of 1 to 6 L/minute in adolescents and adults. A humidifier is used if the nasal cannula will be used at higher flows and for longer periods of time.
Flow rates as low as 250 mL (0.25 L/min) are used to deliver oxygen in infants.
Delivered oxygen concentrations are based on oxygen flow in relation to the patient’s minute volume (tidal volume × rate) and are therefore difficult to accurately predict in infants and young children.
Non-rebreather mask: Delivers oxygen concentrations of approximately 60% to 80% at flow rates of 8 to 10 L/minute.
Non-rebreather masks should be used when a child is in respiratory distress, especially when the etiology of the distress is unknown.
High-flow devices: Provide oxygen at flow rates that meet or exceed the patient’s inspiratory demand.
Venturi mask delivers oxygen concentrations at precisely 24%, 28%, 31%, 35%, 40%, and 50%. This is accomplished by interchanging one of six color-coded adapters.
Aerosol mask, in conjunction with a jet nebulizer, delivers oxygen concentrations of 28% to 100%. An air entrainment port can be opened and closed to adjust the delivered oxygen concentration. The smaller the opening of the entrainment port, the higher the oxygen concentration and the lower the total flow delivered to the patient (Table 4.1).
High-flow nasal cannulas: Specific systems that are designed to deliver heated humidified blended oxygen at higher flow rates that may meet or exceed the patient’s demand. See additional information under “Noninvasive Ventilation” that follows.
Noninvasive Ventilation
Discussion
Noninvasive ventilation plays a key role in the support of pediatric patients who once would have required intubation and mechanical ventilation.
Indications include the need for short-term ventilation, improvement in lung volumes and compliance, and a reduction in oxygen requirements.
Definition
Noninvasive ventilation is a mechanism of providing ventilatory support without the use of an invasive artificial airway (e.g., endotracheal or tracheostomy tube).
Types
BiPAP (bilevel positive airway pressure)
Allows for the separate regulation of the inspiratory and expiratory positive pressure levels as well as the ability to set a mandatory minimal ventilatory rate.
CPAP (continuous positive air pressure)
Allows for spontaneous ventilation, which provides a constant positive airway pressure throughout the respiratory cycle.
High-flow nasal cannula
Gas delivery using a nasal cannula at gas temperatures near body temperature, allowing for highly saturated water vapor.
This highly saturated gas allows for increased flow rates without causing additional discomfort and irritation to the nasal mucosa.
TABLE 4.1 Oxygen Delivery | ||||||||||||||||||||||||||||||||||||
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Assessment and Management
BiPAP/CPAP
Finding the appropriate mask fit for a pediatric patient can be challenging because of the variety of pediatric face shapes and sizes.
The key to successful noninvasive ventilation is a calm cooperative patient. Slowly increasing the patient’s airway pressures to allow for desensitization or the use of small doses of anxiolytics may be required.
Heavy doses of sedation and analgesia are contraindicated.
Periodic breaks off of the BIPAP/CPAP mask are necessary for proper skin assessment and to reduce the risk of skin breakdown.
Skin barrier devices can be applied between the skin and the mask to reduce the risk of skin breakdown.
Adequate patient airway protection is necessary to avoid the potential danger of aspiration.
Not indicated in patients with conditions that reduce the respiratory drive or in cases of respiratory failure.
Care should be taken with patients whose condition interferes with the seal of the mask, such as facial trauma, facial surgery, or the presence of a nasogastric tube.
High-flow nasal cannula
Flow rates are set at 1 to 8 L/minute for infants and young children, although flow rates can be as high as 40 L/minute in older children and adults.
Some sources have postulated that the rate of flow may deliver a level of positive pressure similar to CPAP.
Evaluating patient response
Improvement in arterial blood gases (e.g., increase in oxygenation and decrease in carbon dioxide levels).
Relief of dyspnea.
Improvement in the delivery of medications such as bronchodilators.
Diagnostic evaluation
Consider radiographic imaging while requiring oxygen.
Laryngeal Mask Airway
Brian Eells
Airway Management
Background/Definition
Inflatable cuff sits in hypopharynx, outside larynx.
Creates end-to-end tube with trachea, in comparison to standard endotracheal intubation, which is a tube-within-tube.
Generally considered intermediate to face mask and endotracheal tube.
Useful as rescue device in difficult airway.
Does not “secure” the airway like an endotracheal tube.
Easier blind technique for placement (airway structures not visualized); no laryngoscope needed (Figure 4.1).
Etiology/Types
Originally designed by Dr. Archie Brain.
LMA is LMA North America, now part of Teleflex.
FIGURE 4.1 • Laryngeal Mask Airway. The original LMA design: a size 1 and size 6 LMA-Classic. The two bars over the airway aperture prevent the epiglottis from obstructing the LMA barrel.
TABLE 4.2 Standard Sizing for LAAA
Mask Size
Patient size
1
<5 kg neonate/infant
1.5
5-10 kg infant
2
10-20 kg infant/child
2.5
20-30 kg child
3
30-50 kg child/small adult
4
50-70 kg normal adult
5
70-100 kg large adult
Many LMA versions are available (e.g., Classic, Unique, ProSeal).
Other brands now exist (e.g., i-gel, Ambu Aura-i, Cook air-Q).
LMA Management
Intact airway reflexes preclude proper placement (e.g., biting, coughing, vomiting) (Table 4.2).
Cuff volumes are described by manufacturer.
Proper inflation usually causes slight upper movement of LMA and slight bulging of anterior neck.
Risk of ischemia if cuff is overinflated and/or systemic blood pressure is low.
May cause gastric insufflation if airway pressures exceed gastroesophageal opening pressure (e.g., ×15-25 cm H2O).
 FIGURE 4.2 • Mallampati Scoring. |
Difficult Airway
Brian Eells
Background/Definition
Difficulty with mask ventilation, tracheal intubation, or both.
Etiology/Types
Most assessments and guidelines are based on adult population (e.g., Mallampati classes, ASA’s “Practice guidelines for management of the difficult airway”) (Figure 4.2).
Associated Underlying Conditions
Congenital anomalies (e.g., Pierre Robin sequence, Treacher Collins syndrome)
Tumors (e.g., cystic hygroma)
Infection (e.g., retropharyngeal abscess, epiglottitis)
Oral/dental (e.g., severe overbite, wired teeth/jaw, high-arched palate)
Muscular (e.g., torticollis)
Skeletal (e.g., ankylosis, cervical fracture)
Trauma
Clinical Presentation
Predictors of difficult pediatric laryngoscopy
Age <1 year
ASA physical status 3 or 4
Modified Mallampati class 3 or 4
Oromaxillofacial disorder
Cardiac dysfunction
Evaluation
Modified Mallampati classification system:
Performed in the sitting position, tongue protruded maximally; no phonation.
Class I: Faucial pillars, soft and hard palates, uvula visualized.
Class II: Faucial pillars, soft and hard palates visualized; uvula partially masked by base of tongue.
Class III: Only soft and hard palates visualized; ± base of uvula.
Class IV: Only hard palate visualized.
Thyromental distance
Head and neck movement (particularly neck extension)
Upper lip bite test (ULBT)
Grade I lower incisors can fully cover the upper lip’s mucosa.
Grade II lower incisors can touch the upper lip but cannot fully cover the mucosa.
Grade III lower incisors fail to bite the upper lip.
Body mass index
Larger body mass index associated with difficult airway.
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