Revision of the anatomy and physiology of the skin in relation to the control of body temperature and the temperature-regulating centre, and of the related body mechanisms associated with heat production and heat loss.

Body temperature can be considered as the balance of heat lost from the body and heat gained by the body. Both behavioural and physiological mechanisms maintain core body temperature at 37°C ± 1°C. Abnormal body temperature recordings may be an indication that your patient has an infection, is becoming unwell or is experiencing an abnormal reaction to transfused blood products. The normal range of body temperature is 36–37.5°C, but this may vary, by as much as 0.6°C, according to the site used for measurement and from individual to individual. Factors naturally influencing the patient’s body temperature include the ingestion of fluids and food, hormonal changes, smoking and a number of conditions that interfere with thermoregulation (Neno 2005). It is also important, where possible, to establish your patient’s normal temperature at rest. The following terms are used to describe abnormal temperature ranges:

The upper and lower limits of survival are not precisely known but are thought to be a body temperature of 44°C and 27°C respectively.

The recording of body temperature may be required:

The nature of this practice means that there is a risk of cross infection if the nurse does not adequately clean the thermometers between different patients. Digital electronic probes as well as tympanic thermometers with sheaths/covers still require cleaning with a swab containing 70% isopropyl after patient use to prevent the spread of infection (Carroll 2000).

A variety of disposable thermometers are available for purchase, two of the more common ones being the chemical dot thermometer and the liquid crystal heat-sensitive synthetic strip (Fig. 6.1). These are for single use only, and the manufacturer’s instructions for use must be followed to ensure an accurate recording. These thermometers tend to be used in a community or domestic setting.

Electronic thermometers (Fig. 6.2) have replaced traditional mercury glass thermometers as one of the most popular methods of measuring body temperature in hospitals. The electronic thermometer can be used both orally and axillary and some may have a separate probe for rectal use. In addition to this, the electronic thermometer may require that the correct mode of use, e.g. oral or rectal is selected prior to use. Regardless of which site is selected, research indicates that the accuracy of the recording is dependent upon correct probe placement and the cleanliness of the equipment itself (Carroll 2000). The thermometer will automatically give out an audible signal when the temperature has been recorded. As an accountable nurse it is your personal responsibility that you know how to operate equipment and referral to the manufacturer’s instructions is essential.

Now in widespread use, tympanic thermometers (FIGURE 6.3 and FIGURE 6.4) have a probe with a disposable cover that is inserted into the ear canal. They detect infrared energy that is emitted from the tympanic membrane at the end of the ear canal and surrounding tissue, this then being displayed digitally as a temperature reading. Literature suggests that tympanic thermometers represent a more accurate picture of actual body temperature due to the fact that the tympanic membrane shares the same arterial blood supply as the hypothalamus (the temperature regulating centre within the brain; Gallimore 2004).

The thermometer must be covered by a disposable cover in order to function, and the detection window must be kept clean in order to obtain an accurate result. False readings may arise from incorrect technique, a damaged lens or an inaccurate timing between measurements (Jevon& Jevon 2001).

The axillary site is inappropriate in patients where peripheral circulation is shut down, such as patients with hypothermia (Stevenson 2004). In addition to this the axillary site is the least accurate site in reflecting core body temperature. In elderly patient groups there may be insufficient lean body mass to ensure that the probe is surrounded by skin tissue. The presence of surgical wounds around the site should indicate the avoidance of the site as a means of temperature measurement.