Fever, Chills, and Night Sweats

Excerpt

In health, body temperature is regulated around a set point of 37 ± 1°C, and a circadian temperature rhythm exists in which the highest temperature of each day occurs around 6 p.m. The variance between the highest and lowest core temperature in a given day is usually no more than 1° to 1.5°C. This circadian rhythm may differ among individuals but should be consistent in each person. Relative to the core (blood) temperature, oral temperature tends to be about 0.4°C lower and axillary temperature up to 1°C lower, while rectal temperature, probably because of fecal bacterial metabolism, averages about 0.5°C higher.

Fever is a physiologic disorder in which the temperature is elevated above one's normal temperature. An elevated body temperature may accompany any condition in which exogenous or endogenous heat gain exceeds mechanisms of heat dissipation such as occurs with vigorous exercise, exposure to a warm ambient temperature, or the use of drugs that cause excess heat production or limit heat dissipation. In these situations the hypothalamic "thermostat" remains "set" in the normal range. In true fever, mechanisms to regulate the body temperature above the normal set point are actively operating.

In most patients with fever lasting 1 to 2 weeks, the etiology will be found or the fever will disappear. Occasionally, despite the history, physical examination, laboratory and radiologic procedures, fever (temperature above 38.3°C) will continue beyond 2 to 3 weeks without diagnosis. These patients are said to have fever of undetermined origin (FUO). Although the classic Petersdorf and Beeson definition still has utility, in this era of prospective payment medicine it can be modified to include careful outpatient documentation of fever and lack of diagnosis after careful outpatient evaluation. The critical aspects of any definition of FUO are documentation of fever (>38.3°C with a supervised electronic thermometer) and allowance of adequate time for the vast majority of self-limited viral illnesses to run their course.

Chills are the subjective reports of shivering or shaking associated with rapid changes in body temperature. They result from involuntary muscle contractions that occur in response to a sudden lowering of body temperature below the prevailing set point.

Night sweats are subjective reports of nocturnal sweating that results from an exaggeration of the normal circadian temperature rhythm.