Clinical meaning
Drowning is defined as the process of experiencing respiratory impairment from submersion or immersion in liquid. The pathophysiology centers on two primary organ injuries: pulmonary damage and hypoxic-ischemic brain injury.
Pulmonary pathophysiology: When water is aspirated (even as little as 1-3 mL/kg), it disrupts the surfactant layer lining the alveoli. Surfactant normally reduces alveolar surface tension, preventing alveolar collapse at end-expiration. Loss of surfactant leads to alveolar collapse (atelectasis), decreased lung compliance, ventilation-perfusion (V/Q) mismatch, and intrapulmonary shunting — all producing profound hypoxemia. BOTH freshwater and saltwater aspiration produce similar clinical outcomes (the historical distinction between freshwater causing dilutional hyponatremia and saltwater causing hemoconcentration is clinically insignificant at the volumes typically aspirated). Aspirated water also triggers an intense inflammatory response in the alveolar epithelium, with neutrophil infiltration and capillary leak leading to non-cardiogenic pulmonary edema (ARDS). This can develop within hours of the submersion event and may progress over 24-72 hours — hence the need for observation even in initially asymptomatic patients who aspirated water.
Neurological pathophysiology: The brain is the organ most vulnerable to hypoxic injury. After 4-6 minutes of complete cerebral anoxia, irreversible neuronal death begins. The hippocampus, cerebral cortex, basal ganglia, and cerebellum are most susceptible. After resuscitation, secondary brain injury can occur from reperfusion injury (reactive oxygen species, excitotoxic glutamate release, calcium-mediated cell death), cerebral edema, and loss of autoregulation. The primary determinant of neurological outcome is the DURATION OF SUBMERSION and the DURATION OF HYPOXIA before effective oxygenation and circulation are restored.