Fever

DEFINITION
Higher than normal body temperature because of a changed thermoregulatory set point in the hypothalamus; normal body temperature in dogs and cats is 100.2–102.8°F (37.8–39.3°C) Fever of unknown origin (FUO)—at least 103.5°F (39.7°C) on at least four occasions over a 14-day period and illness of 14 days' duration without an obvious cause

PATHOPHYSIOLOGY
Exogenous or endogenous pyrogens cause release of endogenous substances (e.g., interleukin-1 and prostaglandins) that reset the hypothalamic thermoregulatory center to a higher temperature, activating appropriate physiologic responses to raise the body temperature to this new set point. Physiologic consequences include increased metabolic demands, muscle catabolism, bone marrow suppression, heightened fluid and caloric requirements, and possibly disseminated intravascular coagulation (DIC) and shock.