Fever

Abstract

Fever is defined as any rise of body temperature above 37.8 °C (100 °F). It is not in the purposes of this chapter to describe in details the pathophysiology behind fever. Nevertheless, briefly, body temperature is regulated by the hypothalamus, which balances heat produced by metabolic activity with the heat lost from the skin and lungs to maintain a stable body temperature despite environmental variations. Febrile conditions stimulate the hypothalamic thermoregulatory center through exogenous or endogenous pyrogens. Many microbial products and toxins or even whole microorganisms can act as exogenous pyrogens. In addition, a number of endogenous pyrogens (e.g., interleukins 1 and 6, tumor necrosis factor, interferons, and others) also termed as pyrogenic cytokines are produced by human immune cells and endothelial cells during inflammation. As a response to pyrogens, the hypothalamic thermoregulatory center stimulates a systemic reaction including heat loss preservation in the periphery (vasoconstriction) and increase in heat production through raised metabolism and autonomic muscle activity (shivering). After pyrogenic stimulus has subsided, the hypothalamus increases heat loss through peripheral vasodilation and sweating until body temperature reaches normal levels.