Fever, or PYREXIA, is the abnormal rise in body TEMPERATURE that frequently accompanies disease in general.
Causes The cause of fever is the release of fever-producing proteins (pyrogens) by phagocytic cells called monocytes and macrophages, in response to a variety of infectious, immunological and neoplastic stimuli. The lymphocytes (see LYMPHOCYTE) play a part in fever production because they recognise the antigen and release substances called lymphokines which promote the production of endogenous pyrogen. The pyrogen then acts on the thermoregulatory centre in the HYPOTHALAMUS and this results in an increase in heat generation and a reduction in heat loss, resulting in a rise in body temperature.
The average temperature of the body in health ranges from 36·9 to 37·5 °C (98·4 to 99·5 °F). It is liable to slight variations from such causes as the ingestion of food, the amount of exercise, the menstrual cycle, and the temperature of the surrounding atmosphere. There are, moreover, certain appreciable daily variations, the lowest temperature being between the hours of 01.00 and 07.00 hours, and the highest between 16.00 and 21.00 hours, with triﬂing ﬂuctuations during these periods.
The development and maintenance of heat within the body depends upon the metabolic oxidation consequent on the changes continually taking place in the processes of nutrition. In health, this constant tissue disintegration is exactly counterbalanced by the consumption of food, whilst the uniform normal temperature is maintained by the adjustment of the heat developed, and of the processes of exhalation and cooling which take place, especially from the lungs and skin. During a fever this balance breaks down, the tissue waste being greatly in excess of the food supply. The body wastes rapidly, the loss to the system being chieﬂy in the form of nitrogen compounds (e.g. urea). In the early stage of fever a patient excretes about three times the amount of urea that he or she would excrete on the same diet when in health.
Fever is measured by how high the temperature rises above normal. At 41.1 °C (106 °F) the patient is in a dangerous state of hyperpyrexia (abnormally high temperature). If this persists for very long, the patient usually dies.
The body’s temperature will also rise if exposed for too long to a high ambient temperature. (See HEAT STROKE.)
Symptoms The onset of a fever is usually marked by a RIGOR, or shivering. The skin feels hot and dry, and the raised temperature will often be found to show daily variations – namely, an evening rise and a morning fall.
There is a relative increase in the pulse and breathing rates. The tongue is dry and furred; the thirst is intense, while the appetite is gone; the urine is scanty, of high speciﬁc gravity and containing a large quantity of solid matter, particularly urea. The patient will have a headache and sometimes nausea, and children may develop convulsions (see FEBRILE CONVULSION).
The fever falls by the occurrence of a CRISIS – that is, a sudden termination of the symptoms – or by a more gradual subsidence of the temperature, technically termed a lysis. If death ensues, this is due to failure of the vital centres in the brain or of the heart, as a result of either the infection or hyperpyrexia.
Treatment Fever is a symptom, and the correct treatment is therefore that of the underlying condition. Occasionally, however, it is also necessary to reduce the temperature by more direct methods: physical cooling by, for example, tepid sponging, and the use of antipyretic drugs such as aspirin or paracetamol.