Temperature

Excerpt

Normal body temperature is considered to be 37°C (98.6°F); however, a wide variation is seen. Among normal individuals, mean daily temperature can differ by 0.5°C (0.9°F), and daily variations can be as much as 0.25 to 0.5°C. The nadir in body temperature usually occurs at about 4 a.m. and the peak at about 6 p.m. This circadian rhythm is quite constant for an individual and is not disturbed by periods of fever or hypothermia. Prolonged change to daytime-sleep and nighttime-awake cycles will effect an adaptive correction in the circadian temperature rhythm. Normal rectal temperature is typically 0.27° to 0.38°C (0.5° to 0.7°F) greater than oral temperature. Axillary temperature is about 0.55°C (1.0°F) less than the oral temperature.

For practical clinical purposes, a patient is considered febrile or pyrexial if the oral temperature exceeds 37.5°C (99.5°F) or the rectal temperature exceeds 38°C (100.5°F). Hyperpyrexia is the term applied to the febrile state when the temperature exceeds 41.1°C (or 106°F). Hypothermia is defined by a rectal temperature of 35°C (95°F) or less.