Skip to Main Content


In this chapter we discuss the vital signs (temperature, pulse, respirations, and blood pressure [BP]), followed by measures of body size (height, weight, and body mass index [BMI]), and finish with assessment of pain.

Vital Signs

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 the skin temperature, the pulse, and the respirations as prognostic signs. More recently, the BP has been found to have similar predictive strength.

These signs have played a major role in the history of medicine. In the nineteenth century, entire texts were written on the interpretation of pulse, fever, and respiratory patterns. It is now apparent that these signs are not sufficient to establish a specific diagnosis. On the other hand, they are sensitive indicators of disease and are useful in forming pathophysiologic hypotheses and a differential diagnosis. They remain 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 and seek shade or a cooler environment. Decreased body temperature is countered by shivering (increasing heat generation in muscles) and by behavioral adaptations such as putting on clothes and seeking warmer environs. Deviations of body temperature indicate changes in the set point, increased heat production, decreased heat dissipation, failure of regulatory systems, or any combination of those.

The patient’s temperature is recorded 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 temperatures
Normal body temperature

Internal body temperature is maintained within a narrow range, ±0.6°C (1.0°F), in each individual. However, the population range of this set point varies from 36.0°C to 37.5°C (96.5–99.5°F) making it impossible to know an individual’s normal temperature without an established baseline. Without a baseline it is reasonable to regard an oral temperature above 37.5°C (99.5°F) and a rectal temperature ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.