Key messages

• The occurrence of fever should initiate an investigation for an underlying cause which, once found, should be treated.

• Very high fevers are dangerous, whereas mild pyrexia may be protective.

• Antipyretics and antimicrobial agents can be helpful.

• Neutropenia, AIDS, immunosuppression, and infection in prosthetic heart valves and during pregnancy require special consideration. Introduction

The development of elevated body temperature in response to infection may be a protective adaptive response. Blockade of the febrile response with salicylates in rabbits with bacterial or viral infection has been shown to reduce survival ( Moltzl993). In humans, several retrospective clinical trials have shown a correlation between the development of 'moderate' fever and survival from bacterial peritonitis and bacteremia.

Similarly, in sepsis syndrome, those patients with hypothermia have a poorer outcome than those who develop fever. However, it is unclear whether hypothermia in such a setting is itself the mediator of reduced survival or a marker of more severe underlying pathology.

Several possible mechanistic explanations for the beneficial effects of fever have been proposed. There is evidence that neutrophil chemotaxis and phagocytosis are enhanced.

Very high temperatures (> 40 °C) cause neurological dysfunction, neuronal damage, and cardiac arrhythmias, and should always be treated. However, it is less clear whether moderate elevation of body temperature is detrimental. The major argument for treating fever is related to the increased demands that pyrexia makes upon

oxygen consumption and delivery. Cooling febrile intensive care unit (ICU) patients by 2.4 °C reduces Vo2 and energy expenditure by about 20 per cent. This is associated with a reduction in cardiac output from 8.4 to 6.5 l/min (MiDihoys, 199.5). Thus, when oxygen delivery is limited or hypoxemic respiratory failure is a potential problem, cooling the febrile patient may result in a considerable reduction in the load upon the cardiorespiratory system. Such reduced requirements are likely to be beneficial. In addition, the symptomatic distress caused by high fever in patients who are not sedated should not be forgotten.

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