A rise in temperature can be regarded as a normal response, in that it is part of the autonomic response to create an environment inhospitable for bacteria and organisms, and it is also a favourable environment for antibiotics (Fletcher et al. [64]). A post‐operative fever is often a normal inflammatory response to surgery; however, it can also be a manifestation of a serious underlying infectious or non‐infectious aetiology (Annane [5]). If a temperature rises above 40°C (hyperthermia), it is dangerous and may indicate that the patient's regulatory systems have failed (Kiekkas et al. [94]).

It is common practice to try to reduce fever with medications (such as antipyretics) and physical cooling methods (O'Donnell and Waskett [146]). Antipyretics, including paracetamol and ibuprofen, can mask the function of the hypothalamus by reducing temperature while hiding the underlying signs of disease (Chiumello et al. [42]). It is thought that these drugs inhibit the inflammatory action of prostaglandins, affecting the hypothalamus by temporarily resetting the thermostat to a normal level (Marieb and Keller [111]). Currently the evidence on how to reduce fever in practice is weak and does not support the routine administration of antipyretic therapies (Drewry et al. [56]). Therefore, nurses should assess patients individually, using antipyretic therapies selectively and with caution (Tait et al. [194]).

It is recommended by many studies that antipyretic treatment should begin with drug administration and proceed with external cooling, but the adverse effects of both methods should be considered (Kiekkas et al. [94]). A large multi‐centre trial looking at the effects of external cooling alone in septic patients did, however, find that this method was beneficial and safe (Schortgen et al. [182]). Various surface and endovascular automatic cooling devices allowing tight temperature control are available, such as air and water circulating blankets (Doyle and Schortgen [55]). There is little evidence to support fanning for temperature control, and this is usually only considered for patient comfort. Fanning can actually increase body temperature as it can stimulate a compensatory response by the hypothalamus, initiating heat‐gaining activities such as shivering and peripheral vasoconstriction, which could compromise unstable patients by depleting their metabolic reserve (Gardner [68], Young et al. [219]). Shivering not only impedes thermal control but also increases oxygen consumption (Doyle and Schortgen [55]).

Healthcare professionals should be aware of the side‐effects associated with cooling techniques, such as:

Comfort measures, in addition to reassurance, may include:

A low temperature can lead to complications such as cardiac arrhythmias and hypotension, as well as fluid and electrolyte shifts (Wilkinson et al. [215]). Therefore, immediate management should address these aspects and focus on preventing further heat loss and rewarming the body in order to increase core temperature. There is an increased risk of mortality and morbidity with a body temperature below 32°C (Perlman et al. [160]).

There are three basic types of hypothermia treatment: passive external rewarming, active external rewarming and active internal rewarming (Perlman et al. [160]). Passive external rewarming involves removing wet clothing and providing more insulation for patients with mild hypothermia (32–35°C), who are neither neurologically nor cardiovascularly compromised and are still able to generate heat (Sequeira et al. [184]). Active external methods are advised for moderate (28–32°C) accidental hypothermia and patients with no cardiac co‐morbidities; they include forced‐air blankets, warm blankets and heating pads (Perlman et al. [160]). Active internal methods are reserved for patients who have severe hypothermia (<28°C) and are haemodynamically unstable (Sequeira et al. [184]). Internal rewarming restores temperature to normal levels at a faster rate than surface methods and is associated with rapid normalization of cardiac output (Perlman et al. [160]). Active internal methods include the use of warmed intravenous fluids, such as saline or blood. The fluids must be warmed because a 2 L crystalloid bag administered at the usual temperature of 18°C will decrease a patient's core temperature by about 0.6°C (Zaman et al. [220]). Other active internal techniques include warmed oxygen administration and bladder, peritoneal or thoracic lavage (Perlman et al. [160]).

During any rewarming process, attention must be paid to speediness, as rewarming can cause vasodilation and the patient's metabolic rate can change rapidly (RCUK [173]). Rebound hyperthermia is associated with increased mortality and neurological morbidity (Winters et al. [216]). The optimal rate is unknown but 0.25–0.5°C per hour is recommended (RCUK [173]). For both active external and internal treatment types, specific training and knowledge of the associated devices and products are necessary (Perlman et al. [160]).