infectious diseases
Fever
Pathophysiology of Fever
Body temperature is determined by the balance between heat production by tissues, particularly the liver and muscles, and heat loss from the periphery. Normally, the hypothalamic thermoregulatory center maintains the internal temperature between 37°and 38°C. Fever results when something raises the hypothalamic set point, triggering vasoconstriction and shunting of blood from the periphery to decrease heat loss; sometimes shivering, which increases heat production, is induced. These processes continue until the temperature of the blood bathing the hypothalamus reaches the new set point. Resetting the hypothalamic set point downward (eg, with antipyretic drugs) initiates heat loss through sweating and vasodilation. The capacity to generate a fever is reduced in certain people (eg, those who are very old, very young, or who have an alcohol use disorder). Pyrogensare substances that cause fever. Exogenous pyrogens are usually microbes or their products. The best studied are the lipopolysaccharides of gram-negative bacteria (commonly called endotoxins) andStaphylococcus aureustoxin, which causes toxic shock syndrome. Fever is the result of exogenous pyrogens that induce release of endogenous pyrogens, such as interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), and IL-6 and other cytokines, which then trigger cytokine receptors, or of exogenous pyrogens that directly trigger Toll-like receptors. Prostaglandin E2 synthesis appears to play a critical role. Although many patients worry that fever itself can cause harm, the modest transient core temperature elevations (ie, 38 to 40°C) caused by most acute infections are well tolerated by healthy adults. , phencyclidine), anesthetics, or antipsychotic drugs (see Neuroleptic Malignant Syndrome ). At this temperature, protein denaturation occurs, and inflammatory cytokines that activate the inflammatory cascade are released. As a result, cellular dysfunction occurs, leading to malfunction and ultimately failure of most organs; the coagulation cascade is also activated, leading to Because fever can increase the basal metabolic rate by about 10 to 12% for every 1°C increase over 37°C, fever may physiologically stress adults with preexisting cardiac or pulmonary insufficiency. Fever can also worsen mental status in patients with dementia. Fever in healthy children can cause Febrile Seizures . 