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Medical thermometers are used for measuring human body temperature, with the tip of the thermometer being inserted either into the mouth (oral temperature), under the armpit (axillary temperature), or into the rectum via the anus (rectal temperature).
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Classification, by technology
The traditional mercury-filled medical thermometer works in the same way as a meteorological maximum thermometer. The thermometer consists of a mercury-filled bulb attached to a small tube. There is a constriction in the neck close to the bulb. As the temperature rises, the force of the expansion pushes the mercury up the tube through the constriction. When the temperature falls, the column of mercury breaks at the constriction and cannot return to the bulb, thus remaining stationary in the tube. To reset the thermometer, it must be swung sharply.
When it is designed for use in humans, the typical range of this kind of thermometer is from about 89.6°F to 109.4°F or 35°C to 42°C. The temperature is obtained by reading the scale inscribed on the side of the thermometer.
In the 1990s, mercury-based thermometers were found too risky to handle and have largely been replaced with electronic digital thermometers, or, more rarely, thermometers based on liquids other than mercury (such as heat-sensitive liquid crystals). Other modern options include digital Infrared contact or non-contact thermometers, which are also called scanner thermometers. Most medical thermometers may be used to take oral, axillary, vaginal, or rectal temperatures.
To eliminate the risk of patient cross-infection, disposable single-use clinical thermometers and probe covers are employed in clinics and hospitals.
Basal thermometer
A basal thermometer is a thermometer used to take the basal (base) body temperature, the temperature upon waking. Compared to daytime temperatures, basal body temperatures are much less affected by environmental factors such as exercise and food intake. This allows small changes in body temperature to be detected, such as those caused by ovulation or changes in thyroid function.
Glass fever thermometers typically have markings every 0.2°F (0.1°C). Basal thermometers require accuracy of at least 0.1°F (0.05°C), so special glass basal thermometers are sold separately from glass fever thermometers. All digital thermometers generally read to at least 0.1°F (0.05°C) and so are suitable for monitoring basal temperatures. Some digital thermometers are marketed as "basal thermometers" and have extra features such as a larger display, expanded memory functions, or beeping to confirm the thermometer is placed properly.
Classification, by location
Oral
Oral temperature may only be taken from a patient who is capable of holding the thermometer in their mouth correctly and securely, which generally excludes small children or people who are overcome by coughing, weak, or vomiting. (This is less of a problem with fast-reacting digital thermometers, but was certainly an issue with mercury thermometers, which took several minutes to register a temperature.) Another counter-indication is if the patient has drunk a hot or cold liquid beforehand, in which case one has to wait or use another method.
Rectal
Rectal temperature-taking, especially if performed by a person other than the patient, should be facilitated with the use of lubricant (such as petroleum jelly (now discouraged) or a water-based personal lubricant). Although rectal temperature is the most accurate, this method may be considered embarrassing in some countries or cultures, especially if used on patients older than young children; and, if not taken the correct way, a rectal temperature-taking can be uncomfortable and in some cases painful for the patient. Rectal temperature-taking is considered the method of choice for infants for the general public and the rectal route is also desirable in infants from a nursing point of view.[1]
Ear and forehead
Other kinds of medical thermometers exist, such as the tympanic thermometer that measures the temperature of the tympanum by infrared measurement, and the band thermometer that is applied to the patient's brow.
References
- ^ Fundamentals of Nursing by Barbara Kozier et al, 7th edition, p. 495
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- This page was last modified on 27 August 2008, at 06:17.
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