Although asphyxia literally means no pulse (in Greek), it represents an inability to breathe and therefore suffocation. Failure of gas exchange is characterized by hypoxemia and hypercarbia, as originally defined by J.B.S. Haldane. A mechanistic classification of asphyxia (Table 55.1) includes a diversity of pathophysiological processes that preclude movement of gas from the upper airway to the alveoli and ultimately to the tissues, the cells, and then to the mitochondria, thereby sustaining oxidative metabolism in vital organs.

Asphyxia is a cause of sudden death, but in contrast to primary cardiac causes, it more often presents with bradycardia and asystole rather than ventricular fibrillation (VF). In children, normothermic cardiac arrest is predominantly due to asphyxia. Asphyxia is also the predominant mechanism of cardiac arrest in neonates and in infants due to the so-called sudden infant death syndrome, Status asthmaticus is an important cause of asphyxia. The most frequent cause is failure of respiratory muscle function. Outcomes are worsewhenVF evolves during asphyxial cardiac arrest than after primary VF in adults.

Anoxia or hypoxia is defined by critical reductions in arterial oxygen saturation (SaO2) or arterial oxygen tension (PaO2). Hypercarbia is defined by increases in arterial carbon dioxide tension (PaCO2) in settings of inadequate alveolar ventilation and usually in association with hypoxia.