Beyond hypothermia: mechanisms of death, rescue, and prevention in cold water immersion.

Cold water immersion (CWI) is a significant cause of open-water drowning mortality. Epidemiological data challenge the prevailing assumption that hypothermia is the primary mechanism of death, pointing instead to acute responses that precede core cooling. The four-stage model (cold shock response, swimming failure, hypothermia, and circum-rescue collapse) provides a framework for understanding the sequential threats faced by an immersion victim. The cold shock response, triggered within seconds of immersion, can cause death through aspiration, hypocapnia-induced cerebral hypoperfusion, and cardiac arrhythmia before core temperature begins to fall; autonomic conflict and underlying channelopathies are candidate mechanisms for sudden arrhythmic death in susceptible individuals. Swimming failure follows as peripheral neuromuscular cooling impairs motor function at near-normal core temperatures. Hypothermia develops only after sustained exposure, and in most cold water drowning deaths it occurs after aspiration-induced hypoxic arrest rather than as the primary cause of death. Circum-rescue collapse, driven primarily by the abrupt loss of hydrostatic pressure on extraction, also carries significant mortality risk. Although fewer than 10% of drowning victims present in a shockable rhythm, when such a rhythm is encountered it should prompt investigation for a primary arrhythmic cause that may have precipitated submersion. This narrative review examines the four-stage model of CWI in light of these developments and addresses the modifying effects of alcohol and psychoactive substances, self-rescue strategies, and implications for prehospital management.