Near-drowning and hypothermia.

The term near-drowning is applied to a submersion victim who is taken to an emergency facility and survives 24 hours.1 The quality of survival is not mentioned, but permanent brain damage is common owing to the brain's vulnerability to asphyxia. In Canada, water temperatures may range from 150C to less than 50C throughout most of the year. When a child falls into very cold water but does not remain totally submerged, the body temperature decreases within 5 to 20 minutes to levels of moderate hypothermia (340 to 280C or less). This cooling, termed immersion hypothermia, may cause death by several mechanisms, but, paradoxically, it protects the brain from hypoxia. If rescue occurs within 10 to 30 minutes complete recovery is possible. The term submersion hypothermia is applied when immersion hypothermia is complicated by submersion and asphyxia. Although cooling and drowning may occur separately, simultaneously or sequentially, each process is distinct and requires different treatment. It is well known that when an inadequately clothed person suffers prolonged exposure to cold, accidental hypothermia may develop.2 Immersion hypothermia is an accelerated version of the same process. No amount of shivering or exercise can compensate for the great heat loss that occurs when one is immersed in icy water. The cooling process is more rapid in vigorous swimmers owing to skeletal muscle vasodilatation and the consequent accelerated heat loss from the extremities. Children are even more vulnerable because of their larger surface area relative to body volume and their lack of insulating fat. The temperature of the water is crucial, for the rapidity of cooling and death are directly related. A water temperature below 12 0C causes paralysis of precapillary sphincters, which allows unimpeded blood flow through the cutaneous capillaries.3 When the temperature of the water is 00C death usually occurs within 1 hour, whereas when it is 15 0C death usually occurs within 6 hours. However, when the temperature is 200C or higher almost all persons survive.4 If a person is properly supported by a life-jacket the head remains above the surface of the water; therefore asphyxia will not occur. Brain damage will only develop after cardiorespiratory failure. Several mechanisms leading to cardiac arrest may cause death from immersion hypothermia. The usual course of events is a relentless reduction of core temperature, with delirium when it is 35 0C, unconsciousness when 320C and spontaneous ventricular fibrillation when less than 28 0C. ' It is important to appreciate that in this situation cooling precedes the development of bradycardia and subsequent cardiac arrest. The sequence is similar to that of elective hypothermia for cardiovascular operations, and it is therefore not too surprising that a person can make a complete neurologic recovery after much longer periods of immersion and cardiac arrest than previously thought possible. Death from immersion hypothermia may also occur as a result of two less common mechanisms associated with a poorer prognosis. Rarely the sudden shock of entering icecold water causes immediate ventricular fibrillation (the immersion syndrome6) before preliminary cooling has occurred. More frequently, unconsciousness from cooling leads to cessation of swimming and subsequent drowning, or, if the person is properly supported, cooling continues until cardiorespiratory arrest occurs (usually at a core temperature of 250 C). Obviously, core temperature and duration of bradycardia or cardiac arrest are crucial factors that affect potential recovery, but the exact limits are unknown. Therefore, treatment must be instituted in all cases, and resuscitation must be continued, regardless of the time required, until the body temperature reaches at least 300C and cerebral death is obvious. When rescued, all these persons appear to be dead, but if cardiorespiratory arrest has not occurred the chances of complete recovery are excellent if proper treatment is given. Oxygen should be administered by mask, and warm blankets should be applied. The patient should be handled gently so that ventricular fibrillation is not triggered during transportation of the patient to hospital. If it is unknown whether cardiac arrest has occurred, closed-chest massage and artificial respiration should be started immediately. These two measures must be continued