Chapter 32 Hypothermia and hyperthermia
Although Canadians write more about hypothermia and Saudis write more about hyperthermia, in fact neither condition is rare in Australia. Heat waves and fun runs occur every year in every Australian city. At the opposite end of the spectrum hypothermia is a regular accompaniment to injury and disease throughout the year, and can occur in summer—for example when nursing home patients are left scantily clothed under the air conditioner to cool them. It is important too to remember that the average multiple trauma patient in any country will become hypothermic unless specific preventive steps are taken.
HYPOTHERMIA
This condition is defined as a core temperature < 35°C. It is classified in Table 32.1.
| Temperature (°C) | Grade | Signs |
|---|---|---|
| 35–32 | Mild | Shivering/apathy |
| 32–28 | Moderate | Confusion ↓PR ↓BP |
| < 28 | Severe | CV failure |
Diagnosis and differential diagnosis
If temperature is not a routine observation on every patient, ensure it is taken in those patients who are potential hypothermia candidates, as outlined in Table 32.2.
| Conditions associated with accidental hypothermia |
| Trauma that limits protective mechanisms, e.g. neck of femur (NOF) |
| Overdose |
| Alcoholism |
| Conditions that may cause hypothermia |
| Sepsis |
| Myxoedema or adrenal insufficiency |
| Parkinsonism (failure to shiver) |
| Wernicke’s encephalopathy |
| Drugs, e.g. phenothiazines; beta-blockers; clozapine; sedatives |
| Hypoglycaemia; diabetic ketoacidosis (affect the thermostat) |
| Pancreatitis |
| Myocardial infarction or other cause of low CO |
| Malnutrition/anorexia |
| Burns; extensive skin rashes (excessive heat loss) |
| Conditions that hypothermia may be mistaken for |
| Cerebrovascular accident (CVA) |
| Dementia; confusion in the elderly; delirium |
| Hypoglycaemia |
| Myocardial ischaemia |
| Drunk and disorderly |
| Myxoedema |
Investigations and management
Mild hypothermia (35–32°C)
1. Stop further heat loss. The most powerful way to prevent heat loss in any emergency department patient is to stem conduction and radiation loss—i.e. remove wet clothes and provide a blanket or space blanket. This is also called passive external rewarming, because prevention of heat loss allows the patient’s own metabolism to raise body temperature.
4. Apply a Bair Hugger, if available. This method of active external warming using hot air is commonly available and unlikely to cause rewarming shock or burns. Active warming, however, is not vital unless the patient is incapable of generating heat because of systemic disease or a condition (e.g. CVA) that has reset the temperature centre. If a Bair Hugger is used, do not exceed a rise of 2°C/h. It is probably better to leave the arms exposed because the main risk is that sequestered cold blood will be restored to the circulating pool by skin vasodilation, causing an afterdrop in the core temperature. This risk is less from the trunk than the limbs.
5. Give O2 and monitor O2 saturation. If the saturation monitor will not read because of vasoconstriction, warm the finger or even do a digital block to overcome vasospasm.
6. Set up IV access and take blood for:
• Blood sugar level (BSL). Physiologically, hypothermia causes firstly a rise in BSL due to catecholamine-induced glycogenolysis, then reduced insulin secretion. Finally (below 30°C) insulin stops working. But there is a high association with hypoglycaemia in alcoholics, and elderly or malnourished patients may have exhausted glycogen stores by the increased metabolism of shivering. Treat hypoglycaemia but not hyperglycaemia. If rewarming does not correct hyperglycaemia, exclude haemorrhagic pancreatitis (a complication of hypothermia) or diabetic ketoacidosis (a cause of hypothermia).
• Urea and electrolytes. Fluid shifts and renal dysfunction mean that Na and K can go in either direction. Minor changes in the initial results do not require treatment and can simply be observed during rewarming. Significant changes should be treated and may be a clue to the underlying cause of the hypothermia.
• Full blood examination (FBE). Expect the haematocrit to be high (due to cold diuresis—an attempt to compensate for central fluid overload due to peripheral vasoconstriction) and the WCC and platelets to be normal or low (due to sequestration). A normal Hb/Ht may indicate anaemia and a normal WCC does not rule out infection. Thus the main reason for doing the tests is that a high WCC increases suspicion of an underlying disease process.
• Troponin. Patients who become hypothermic during surgery have a higher incidence of myocardial events. Subendocardial infarctions have been found at autopsy in the absence of ECG changes. In elderly patients, repeat troponin after rewarming.
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