The vital signs, temperature, pulse, respirations, and blood pressure (BP), are discussed in the first part of this chapter. We discuss measures of body size (height, weight, and body mass index) in the second and pain assessment in the final part of the chapter. The former have direct bearing on health risk assessment, and the latter is essential in the initial evaluation and ongoing management of patients with acute or chronic illness or injury.
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. More usefully, the amount of deviation from normal is correlated, for each parameter and especially in combination, with the magnitude of threat to life. 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. With the advent of modern diagnostic methods, it is now apparent that most of these signs are of insufficient specificity to be of much utility in establishing a specific diagnosis. On the other hand, they are sensitive indicators of the presence of disease and are useful in generation of pathophysiologic hypotheses and differential diagnosis. They remain strongly correlated with severity of illness and outcome.
Internal body temperature is tightly regulated to maintain normal cellular function of vital organs, particularly the brain. Deviation of temperature by more than 4°C above or below normal can produce life-threatening cellular dysfunction. Regulation of internal temperature is controlled by the hypothalamus, which maintains a set point for temperature. The autonomic nervous system plays a key role in maintaining 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 radiates heat away by conductive loss while production of sweat increases evaporative heat loss. Behavioral adaptations are also important; in hot conditions, people become less active and seek shade or a cooler environment when they are able. Decreased body temperature is opposed by increased heat generation in muscles by shivering 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.
Record the patient's temperature at each visit. Doing so, establishes an individualized baseline for future reference and detects deviations from this baseline, 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.