This leads to hypoxemia. In young children suddenly immersed in cold water, the mammalian diving reflex may occur and produce apnea, bradycardia, and vasoconstriction of nonessential vascular beds with shunting of blood to the coronary and cerebral circulation. The target organ of submersion injury is the lung. Injury to other systems is largely secondary to hypoxia and ischemic acidosis. Fluid aspirated into the lungs produces vagally mediated pulmonary vasoconstriction and hypertension.
Freshwater moves rapidly across the alveolar-capillary membrane into the microcirculation.
In salt water near drowning, surfactant washout occurs, and rapid exudation of protein-rich fluid into the alveoli and pulmonary interstitium is observed. Compliance is reduced, direct alveolar-capillary basement membrane damage is seen, and shunting occurs. This results in rapid production of serious hypoxia. Fluid-induced bronchospasm also may contribute to hypoxia. Submersions as long as an hour can in some circumstances be fully resuscitated.