Pediatric emergency medicine trisk 1384 1384
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Respiratory distress results from dysfunction or disruption of the respiratory
tract and/or systems that control or modulate respiration.
Respiratory failure is the inability to meet the metabolic demand for O2
(hypoxia) or to eliminate CO2 (hypercapnia). Criteria for defining respiratory
failure vary widely; one set of criteria is presented in Table 71.1 . Hypoxia can be
categorized on the basis of mechanism. Arterial hypoxemia results from an
inability to deliver adequate O2 to the blood, low atmospheric PO2 , diffusion
impairment, anatomic or physiologic shunt, or increased metabolic demand.
Anemic hypoxia is the result of the blood’s inability to deliver adequate O2 to
tissues as a result of decreased hemoglobin oxygen-carrying capacity.
Hypokinetic, ischemic, or stagnant hypoxia also results in an inability of the
blood to transport O2 to the tissues. Histotoxic hypoxia results from inability to
metabolize O2 at the tissue level as a result. Hypercapnia often contributes to
respiratory failure as a result of hypoxemia and is less commonly the primary
cause.
Infants are at an increased risk of respiratory distress compared with children
and adults because of anatomic and physiologic differences ( Table 71.2 ). These
differences result in greater risk of airway obstruction, less efficient respiratory
effort, limited respiratory reserve, and dysfunction of CNS respiratory control.
DIFFERENTIAL DIAGNOSIS
Establishing a diagnosis for respiratory distress in part depends on localizing the
pathology to a particular organ system. In addition to primary respiratory
etiologies, disease or dysfunction of other organ systems may indirectly result in
respiratory disturbance by compromising respiratory system function or by
stimulating compensatory respiratory mechanisms ( Tables 71.3 to 71.5 ).
Treatment of the underlying cause is essential for definitive treatment of the
respiratory distress.
Respiratory System
Respiratory distress may be caused by upper or lower airway obstruction or by
disorders of the parenchyma or interstitium. Upper airway obstruction is common
in infants and young children in part because of their airway anatomy and
physiology (see Chapter 75 Stridor ). The hallmark of complete upper airway
obstruction is inability to phonate (i.e., no speech, cry, or cough). Manifestations
of upper airway obstruction may also include nasal flaring, stertor or snoring,
gurgling, drooling, dysphagia, hoarseness, stridor, retractions, and paradoxical
chest/abdominal wall movement. In neonates, common causes include nasal
