Chapter 40. Hypothermia

Hypothermia is defined as having a core temperature below 35°C. Clinically, it can be divided into three categories:

• Mild: 32–35°C

• Moderate: 30–32°C

• Severe: below 30°C

and into three groups according to circumstances:

• Immersion – patient has been in water

• Dry – patient is on dry land but has been exposed to low air temperatures

• Urban – such as elderly patients who fall in their home.

The underlying clinical effects are broadly the same for each group.

Heat loss

Heat loss occurs from the body via conduction, convection, radiation and evaporation.

The surface area over which heat is lost is important. Children have a larger surface area for their weight than do adults and hence tend to lose heat more quickly.

The temperature of the human body is normally regulated within strict limits around an average core temperature of 37°C.

Clinical recognition of hypothermia

Cases will be missed unless specific consideration is given to its possible presence. It should be remembered that where hypothermia has occurred in one member of a party, the others will also be at risk and further cases may occur unless corrective action is taken.

**Table 40.1.** Clinical features of hypothermia
Core temperature (°C) ^a	Clinical feature

36	Sensation of cold, stumbling, personality changes, mild confusion
35	Slurred speech, incoordination. Amnesia of events (on recovery)
34	Development of arrhythmias – typically atrial fibrillation
33	Shivering lost – replaced by muscular rigidity
31	Pupils become dilated. Loss of consciousness
30	Insulin ineffective. Risk of spontaneous ventricular fibrillation – often unable to defibrillate
26	Major acid-base disturbance
24	Significant hypotension
23	Apnoea
18	Asystole
^aThese temperatures are a guide and will vary between individuals.

History

The history frequently gives an indication of the likely presence of hypothermia and may well be the only indicator. The following questions should be asked:

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