Hypothermia of both the extremities and the body core continues to be a major problem in cold water diving. Presently, extremity hypothermia of the hands limits cold water diving exposure more so than body core hypothermia. Painful or numb fingers decrease dexterity, safety, work capacity, and increase the risk of developing nonfreezing cold injury (NFCI), which is reviewed. Levels of body core hypothermia, based on rectal core temperature, are mild (35-32), moderate (32-28), and severe hypothermia (below 28 C). As it relates to cold water diving, the pathophysiology of immersion and mild to severe hypothermia is reviewed including thermoregulation and effects on organ systems. The diving response, composed of bradycardia and peripheral vasoconstriction, has been shown in man to not prolong breath-holding time, or influence alveolar gas exchange, such as oxygen consumption. Survival from cold-water near-drowning may be more dependent on hypothermia than previously recognized. The predisposing factors leading to hypothermia during diving operations are discussed. The determination of body core temperature from various sites including new radio pill telemetry is reviewed. The levels of hypothermia by physical exam findings are reviewed in detail. The field treatment of hypothermia is discussed with attention to a review of the literature, recent research, and first aid management guidelines. The prevention of hypothermia during diving operations and current diving medicine research in the active thermal protection of free- swimming divers is reviewed.
