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Body temperature in children


Currently available probe-type digital thermometers are quicker to use, probably more reliable and are much safer. In many countries, the traditional mercury thermometers are being phased out in view of the undesirable effects of mercury if the thermometer is bitten. The digital thermometers give a quick and dependable reading but are expensive. These can be used to measure the temperature on the surface of the skin, inside the mouth or in the rectum. The instructions provided with the instrument should be carefully followed to obtain accurate readings.
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by Dr. B.J.C.Perera Consultant Paediatrician


(June 15, Kandy, Sri Lanka Guardian) The normal human body interior is meticulously maintained around a temperature of 98.60 (degrees) Fahrenheit (F) or 370 (degrees) Celsius (C). All body processes function best at this temperature and there is a sophisticated and complex inherent mechanism that maintains it at this level. The internal temperature is strictly controlled by a Thermoregulatory Centre in the brain which is sensitive to all and any changes in the internal temperature.

The components of the temperature regulating mechanism works like a thermostat. The core body temperature of an individual is the really significant reading and even in a normal person this tends to vary during the different times of the day and with activity levels. In reality, when the temperature is measured it is known that it could fall within a “normal range” around the levels of 98.60 F or 370 C. It is also important to note that the surface temperature of the human body varies even in the same individual depending on the sites at which it is measured.

The body temperature is kept at a very even level by a range of automatic adjustments. Through one mechanism, if one is too hot, the blood flowing through the skin is increased by opening up the tiny capillary blood vessels. This allows the process of radiation to take away excess heat and cool the body. This process is augmented and complemented by sweating. When one is too cold, there is an automatic mechanism to shut down skin blood vessels and conserve heat within the internal organs. If necessary more heat could be generated by shivering.

In many situations the measurement of the body temperature becomes an important tool to assess the health of an individual. This is particularly so in children as fevers are common and are important features of many diseases in them. There are different types of measuring devices that could be used to check the body temperature in children. The time honoured instrument is the traditional mercury thermometer in which the column of mercury may be encased in glass or plastic. The more modern types of instruments include digital thermometers, electronic ear thermometers and measuring strips that could be placed on the surface of the skin.

Currently available probe-type digital thermometers are quicker to use, probably more reliable and are much safer. In many countries, the traditional mercury thermometers are being phased out in view of the undesirable effects of mercury if the thermometer is bitten. The digital thermometers give a quick and dependable reading but are expensive. These can be used to measure the temperature on the surface of the skin, inside the mouth or in the rectum. The instructions provided with the instrument should be carefully followed to obtain accurate readings.

Use exactly as directed

The electronic ear thermometers are easy to use, quick and will give a read-out in seconds. Ear thermometers rely on measuring infrared (heat) radiation from the eardrum. In these special thermometers, to get a reliable temperature measurement, the thermometer must be used exactly as directed and one needs to read the instruction manual or leaflet carefully before using the instrument. Especially with small children, ear thermometers require a steady hand to find the right spot. The ear canal has a natural curve and to ensure that the thermometer is pointing towards the eardrum it may be necessary to pull the top part of your child’s ear gently upwards during the reading. If the child has been lying with his head on a warm pillow, or has just come inside out of the cold, one needs to wait 10 to 15 minutes before the ear thermometer can provide an accurate measurement of body temperature. The instrument is quite expensive.

A body temperature reading can be taken from the mouth, armpit, ear, skin surface or the rectum. The site at which the instrument is used is of paramount importance in recording the temperature. The mercury thermometers could be used under the armpit, inside the mouth and inside the rectum. The selection of the site depends on the age and type of child. In small children the mouth should not be used as there is a risk of the child biting on the instrument. It may also not be possible to keep it in the armpit in some children who are restless and not able to lie still. Checking it rectally is unpleasant for the child. The column of mercury should be shaken down to below the normal range before the procedure and whatever the site that is selected, it is important to keep the thermometer in place for the prescribed period of time.

Although there is no absolutely universal agreement on the duration for which the thermometer has to be kept in place, generally with children who are old enough to co-operate and keep still one needs to keep the thermometer under their armpit for at least 5 minutes. In older children and adolescents oral temperature measurement could be used. The thermometer is placed in the mouth, under the tongue and it will take two to three minutes to measure the temperature accurately. It is important to note that if the child has just eaten or drunk anything hot or cold, one needs to wait for at least 10 minutes before an accurate temperature reading can be taken. Temperature readings from the armpit are not totally reliable and are about 0.5ºC lower than mouth temperature. Although a rectal temperature reading is the most accurate and is quite often used in hospital it is not necessary to be so precise when taking temperature readings at home. Rectal temperature reading is therefore not recommended for home use. Rectal temperatures are the closest to central ‘core’ temperature and are about 0.5ºC (2ºF) higher than readings taken from the mouth or ear.

Thermometer strips that are placed on the child’s forehead are popular but they only provide a rough guide. They are convenient and easy to use. However, they indicate only whether the temperature level is higher than normal. Some even indicate the temperature on the surface but these readings are not very accurate. They aren’t reliable enough for taking an exact measurement, especially in infants and very young children.

Ideal scenario

In an ideal scenario, different methods may be used to advantage according to the age of the child. In a child younger than 3 months, the most reliable reading of the body temperature is by using a digital thermometer to take the rectal temperature.

Electronic ear thermometers aren’t recommended for infants younger than 3 months because their ear canals are usually too small. In children between the ages of 3 months to about 4 years, the best method is to use a digital thermometer to take the rectal temperature or an electronic ear thermometer to take the temperature inside the ear canal. One could also use a digital thermometer to take the temperature under the armpit. In a child older than 4 years a digital thermometer could be used to take the oral temperature if the child is cooperative. However, kids who have frequent coughs or are breathing through their mouths because of stuffy noses might not be able to keep their mouths closed long enough for an accurate oral reading. In such cases an electronic ear thermometer or a digital thermometer under the armpit could be used.

Many a time parents complain of fever in their children by the feeling of warmth detected by placing a hand on the skin of the child. This is not totally reliable. Very high body temperatures may be detected by touching the skin but milder degrees of elevation of the surface temperature cannot be reliably detected by this method. It would be a useful and wise move to invest in a thermometer for the home and to familiarise oneself of the correct way of using it. It is important to note that being able to tell the doctor the exact levels of elevation of the body temperature of children will be most helpful in determining the cause of the problem and arriving at a definitive diagnosis.
- Sri Lanka Guardian

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