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This chapter discusses the vital signs (temperature, pulse, respirations, and blood pressure [BP]), followed by measures of body size (height, weight, and body-mass-index [BMI]), and finishes with pain assessment.


Why are temperature, pulse, respirations, and BP called vital signs? These are the signs of life (L. vitalis, from vita: life); their presence confirms life and their absence confirms death. The more abnormal these parameters become, singly, but especially in combination, the greater the life is threatened. Since ancient times, practitioners have used skin temperature, pulse, and respirations as prognostic signs. More recently, the BP was found to have similar predictive value. Entire texts were written on the interpretation of pulse, fever, and respiratory patterns. It is now apparent that these signs are insufficient for establishing a specific diagnosis. On the other hand, they are sensitive indicators of disordered physiology and are useful in forming pathophysiologic hypotheses and differential diagnoses. They are strongly correlated with severity of illness and outcome.

Body Temperature

Internal body temperature is tightly regulated to maintain vital organ function, particularly the brain. Temperature deviation of more than 4°C above or below normal can produce life-threatening cellular dysfunction. Internal temperature is regulated by the hypothalamus, which maintains a temperature set point. The autonomic nervous system maintains body temperature by regulating blood flow, conducting heat from the internal organs to the skin, and innervating sweat glands. Increasing flow and dilating cutaneous capillaries radiate heat away by conductive loss whereas sweat increases evaporative heat loss. Behavioral adaptations are also important. In hot conditions, people become less active seeking shade or a cooler environment. Decreased body temperature is countered by shivering, which generates heat, and by behavioral adaptations such as putting on clothes and seeking a warmer environment. Sustained temperature deviation indicates a change in the set point, increased heat production, decreased heat dissipation, failure of the regulatory systems, or any combination of those.

Record the patient’s temperature at each visit to establish a baseline for future reference. Deviations from this baseline are either fever or hypothermia. Scales on clinical thermometers are either Fahrenheit or Celsius. Conveniently remembered clinical equivalents are 35°C = 95°F, 37°C = 98.6°F, and 40°C = 104°F.

Normal temperature
Normal body temperature

Internal body temperature is maintained within a narrow range, ±0.6°C (1.0°F). The population range of this set point varies from 36.0°C to 37.5°C (96.5–99.5°F), making it necessary to establish a baseline for each patient. Without a baseline, an oral temperature above 37.5°C (99.5°F) and a rectal temperature over 38.0°C (100.5°F) is considered fever.

Diurnal variation

Daytime workers, who sleep at night, have minimum temperatures between 3 and 4 AM, rising slowly to a maximum between 8 and 10 PM. This ...

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