Chapter 3:	Physical Examination
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III. Temperature

The temperature of the body indicates the amount of heat produced by the activity of changing food into energy. The body loses heat through perspiration, breathing, and the elimination of body wastes. The balance between heat production and heat loss determines the body’s temperature. The average normal body temperature is 98.6° F, with daily variances of about 1° F.

There are a variety of factors, including exercise and infections, that can cause body temperature to increase. When temperature increases, CO₂ production and, O₂ consumption also increase. For example, with every 1° rise in temperature CO₂ production and O₂ consumption increase by nearly 10%. In turn, breathing frequency needs to increase in order to adequately compensate. Logically, declines in temperature produce just the opposite effect. A mild infection may cause the temperature to rise to 102° F, while a temperature over 106° F can be fatal.

Temperatures below normal are called hypothermia. Collapse will occur at 96.0° F, and death normally occurs if temperature goes below 93.0° for any length of time. The most common cause of hypothermis is extensive and prolonged exposure to cold temperatures in the environment. Hypothermia can also be caused by severe head injuries involving damage to the hypothalamus, an important regulatory agent for body temperature. As the body temperature falls to low levels, the hypothalamus initiates shivering to generate heat, and vasoconstriction to conserve heat. Patients with hypothermia may exhibit slow and shallow breathing and reduced pulse rates. Mechanical ventilators in the control need may need to be significantly adjusted in the rate and depth of tidal volumes delivers as the patient’s temperature rises and falls below normal.

The body’s temperature is kept normal by balancing heat production with loss of heat. If the body did not discharge heat generated by metabolism, the temperature would rise about 2° F per hour. Peripheral vasodilatation, sweating, and respiratory ventilation help dissipate body heat.

The patient’s body temperature is most commonly measured by using a glass or electronic thermometer at the site of the mouth, axilla, or rectum. The temperature measured at the rectal site most closely approximates the actual core temperature of the patient’s body. The most acceptable site for measuring adult temperatures is the mouth. If patients have been smoking or ingesting hot or cold liquid, taking of the temperature should be delayed for about 15 minutes to avoid inaccurate measurements.

Oral temperatures should not be taken on patients breathing heated or cooled aerosol via face masks because there is a tendency for erroneous measurements. However, oral temperatures are unaffected by simple oxygen administration via nasal cannula or mask. It is not necessary to remove the oxygen or use the rectal site on patients receiving simple oxygen therapy.