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Selecting a location for measurement

The accuracy of the measurement of body temperature depends on the selection of a suitable location for carrying out the measurement and the use of a suitable procedure. Ideal locations that provide the greatest possible accuracy are invasive.

The body temperature of a healthy person changes during the course of the day and depending on their activity. Basically, a distinction is made between the body core temperature and the surface temperature. The surface temperature is measured on the surface of the skin and is derived from the ambient temperature and the temperature inside the body.

Ideal measurement points are body cavities close to major blood vessels: the mouth, rectum, under-arm and eardrum.

Oral temperature (measurement location: mouth)
The temperature in the posterior sublingual pouch, i.e. the mouth tissue that is far back under the left or right side of the tongue, corresponds most closely to that recorded by invasive techniques. The patient should keep his mouth closed, be able to breathe freely through the nose and should not have consumed any food or drink within the previous 30 minutes.

Normal temperatures are usually between 36.0°C and 37.5°C.

This method should be used for people over the age of 5.

Rectal temperature (measurement location: rectum)
Rectal measurement is an alternative to oral measurement (especially if warm or cold treatments are being applied to the head or throat, with local inflammatory processes, and for babies and toddlers).

The rectal temperature is generally 0.3 °C – 0.4 °C higher than the oral temperature.
The thermometer should not be inserted further than 2-3 cm. A lubricant can be used to make insertion easier.

Axillary measurement (Measurement location: under the arm)
The under-arm is probably the oldest location for determining body temperature. The first temperature investigations by the German physician Wunderlich a century ago were carried out using exclusively axillary measurement. When his findings were published, which led to the introduction of daily temperature measurement in hospitals all over the world, axillary measurement became standard practice.

Axillary measurement is suitable for all age groups.
The time required for accurate measurement is around 5 minutes.

Aural temperature measurement (measurement location: at the ear-drum)
The ear-drum is an ideal location for temperature measurement, as it is supplied with the same blood as the hypothalamus. Unlike “external temperature measurement”, such as oral, axillary and rectal measurement, the body’s core temperatures are measured at the ear-drum.

The measurement result can be obtained after 1 second using an infrared sensor.
The accuracy of this type of measurement depends heavily on the correct use of the thermometer and the design of the measuring tip. Since the aural canal is not straight, it takes some practice to precisely determine the infra-red radiation from the ear-drum using the optical measuring system.

With children who are less than 3 years old, or who are active or restless, the precise positioning of the probe in the ear can cause problems and thus inaccurate measurements.

Very good measurement results can be obtained by pulling gently on the ear, which stretches the auditory canal, making it easier for the probe to reach the ear-drum. If only the auditory canal is reached, the temperature measured may be as much as 1°C below the true body temperature.

Normal temperatures are usually between 35.8°C and 38.0°C.

Forehead temperature measurement (measurement location: forehead – temple)
Here too, it is possible to measure the temperature using infrared sensors. A precise measurement result can be obtained because the forehead is close to major blood vessels. This method of measuring body temperature is perceived as the least unpleasant. The thermometer is placed on the forehead, and an initial infrared sensor determines the highest measured value. At the same time, a second sensor measures the ambient temperature. The difference between the two values gives the body temperature, taking into account the clinical adjustment calculation.