Medical thermometer



Medical thermometers are traditionally mercury-in-glass thermometers 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).

Classification, by technology


The traditional mercury-filled medical thermometer works in the same way as a meteorological maximum thermometer. The thermometer consists of a bulb containing mercury attached to a small tube.the range of this thermometer is from 89.6.F to 109.4.F.  As the temperature rises, the mercury expands and flows up the tube. The temperature is obtained by reading the scale inscribed on the side of the thermometer. There is a constriction in the neck close to the bulb. As the temperature rises, the mercury is forced up through the constriction by the force of the expansion. 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.

In the 1990s, mercury thermometers were found too risky to handle and have largely been replaced with electronic thermometers, or, more rarely, thermometers based on liquids other than mercury. In some places, it may be illegal to sell products which contain mercury, such as thermometers. Both kinds may be used orally, axillarily, or rectally.

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; however, the rectal route is least desirable in infants from a nursing point of view.

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.

Fieberthermometer Koortsthermometer 体温計