Role of apnea in the sudden infant death syndrome: a personal view.

Evidence supporting a role for abnormal apnea in sudden infant deaths is predominantly circumstantial. Investigations of infants having cyanotic episodes have shown four mechanisms for abnormal apnea. The most frequent, prolonged expiratory apnea, is particularly dangerous because it is associated with the rapid onset and progression of hypoxemia and other features suggesting alveolar ventilatory-perfusion mismatch. Seizure-induced apnea, maternally imposed obstructive apnea, and sleep-related upper airway obstructive apnea may also produce severe hypoxemia. Attempts to identify infants at risk of sudden death using measurements of cardiorespiratory variables have to date had limited success. Nevertheless, techniques for more precise, yet non-invasive, monitoring of respiratory function, including oxygenation, have been recently developed and such attempts to identify "at risk" infants must continue. Epidemiologic and pathologic studies have provided considerable support for the "abnormal apnea hypothesis" and need to be integrated with studies on the physiology of living infants. On the basis of the presently available evidence concerning prolonged apnea, it may be possible to prevent a proportion of sudden infant deaths by reducing the exposure of young infants to pertussis, respiratory syncytial virus, or other respiratory tract infections and by improving the prenatal environment.