Recognition of hypothermia
Recognition is based on knowing the signs and observing the patient. The signs may be subtle, so there should be a high level of suspicion of hypothermia in any person behaving abnormally in likely conditions. Patients of hypothermia cannot recognise their own impairment, and so recognition must be done by others. Response cannot be delayed; failure to implement appropriate measures immediately risks the life of the patient.
All party members should be observed, remembering that the occurrence of hypothermia in one member of a party suggests that others may be susceptible. While the body can acclimatise to heat, there is no clear evidence that the body can acclimatise to cold to any significant degree. The combination of exertion and the need to maintain body temperature in a cold environment places a large demand on body energy stores, requiring frequent carbohydrate snacks. Fitness alone does not improve the ability to withstand cold stress, but physical fitness and good nutrition may reduce fatigue or exhaustion when activity and shivering are required for heat generation, and increase the margin of safety in the cold.
Classification of hypothermia
Hypothermia is considered mild if core temperature lies between 35°C and 32°C and profound at core temperatures below 32°C. In most cases of mild hypothermia, the patient is able to rewarm themselves by shivering, provided proper first aid measures are instituted, with prevention of further heat loss being the most important. However, in severe hypothermia, the patient loses the ability to rewarm themselves, there is significant impairment of brain, heart and other bodily functions, and there is grave threat to life. It is virtually impossible to rewarm such a patient in the field, but further heat loss can be minimised by first aid measures. Evacuation should be arranged urgently. While the lowest recorded adult accidental hypothermia survival temperature to date is 16°C, the risk of death is high once core temperatures fall below 32°C.
Early signs of mild hypothermia are forgetfulness, loss of judgement and loss of coordination, particularly of fine movements (e.g. use of fingers). There may be some abnormal behaviour, such as lack of cooperation and apathy. Shivering will occur and may be uncontrollable. Other signs of impaired brain function may occur, such as slurred speech and stumbling gait. The appearance of hypothermia can cover a wide spectrum, ranging from mild, insidious loss of judgement, which may not be immediately apparent, to the obviously stumbling, forgetful person. ‘Paradoxical’ undressing may occur; the inappropriate undressing in a hypothermic patient indicates loss of normal protective behavioural responses. The signs of mild hypothermia may be subtle and easily missed when the party is battling adverse conditions, unless vigilant observation of all party members is maintained.
Profound hypothermia should be suspected when there is marked loss of coordination and marked change in mental function (such as confusion, reduced level of consciousness or coma). Shivering stops and the patient loses the ability to rewarm themselves. The patient will be cold to touch. Breathing becomes shallow and the pulse becomes faint and slow. In very severe cases the patient may have fixed, dilated pupils, be rigid and unresponsive, and without obvious breathing or pulse; they may appear lifeless. Signs of life must be carefully checked for, as they may be present but very hard to detect, as discussed later. The cause of death in hypothermia is cardiac arrest; that is, the heart stops.