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Fever |
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Fever (also known as pyrexia, or a febrile response from the Latin word febris, meaning fever, and archaically known as ague) is a frequent medical symptom that describes an increase in internal body temperature to levels that are above normal (the common oral measurement of normal human body temperature is 36.8±0.7 °C or 98.2±1.3 °F). Fever is most accurately characterized as a temporary elevation in the body’s thermoregulatory set-point, usually by about 1-2°C. Fever differs from hyperthermia, which is an increase in body temperature over the body’s thermoregulatory set-point (due to excessive heat production or insufficient thermoregulation, or both). Carl Wunderlich discovered that fever is not a disease but a symptom of disease.
The elevation in thermoregulatory set-point means that the previous "normal body temperature" is considered hypothermic, and effector mechanisms kick in. The person who is developing the fever has a cold sensation, and an increase in heart rate, muscle tone and shivering attempt to counteract the perceived hypothermia, thereby reaching the new thermoregulatory set-point.
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Diagnosis |
When a patient has or is suspected of having a fever, that person's body temperature is measured using thermometer. At a first glance, fever is present if:
- temperature (in the anus(rectum/rectal) or (in the ear(otic) is at, or higher than 38 degrees Celsius @ 100.4 Fahrenheit
- oral temperature (in the mouth) is at, or higher than 37.5 degrees Celsius (99.5 degrees Fahrenheit)
- axillary temperature (underarm) is at, or higher than 37.2 degrees Celsius (99 degrees Fahrenheit)
However, there are many variations in normal body temperature, and this needs to be considered when measuring fever. The values given are for an otherwise healthy, non-fasting adult, dressed comfortably, indoors, in a room that is kept at a normal room temperature, during the morning, but not shortly after arising from sleep. Furthermore, for oral temperatures, the subject must not have eaten, drunk, or smoked anything in at least the previous fifteen minutes.
Body temperature normally fluctuates over the day, with the lowest levels at 4A.M. and the highest at 6P.M. Therefore, an oral temperature of 37.5C would strictly be a fever in the morning, but not in the afternoon. Normal body temperature may differ as much as 0.4C (0.7F) between individuals or from day to day. In women, temperature differs at various points in the menstrual cycle, and this can be used for family planning (although it is only one of the variables of temperature). Temperature is increased after meals, and psychological factors (like the first day in the hospital) also influence body temperature.
There are different locations where temperature can be measured, and these differ in temperature variability. [Tympanic membrane] [thermometer]s measure radiant heat energy from the tympanic membrane (infrared). These may be very convenient, but may also show more variability.
Children develop higher temperatures with activities like playing, but this is not fever because their set-point is normal. Elderly patients may have a decreased ability to generate body heat during a fever, so even a low-grade fever can have serious underlying causes in [geriatrics]
Temperature is ideally always measured the same moment of the day, in the same way, after the same amount of activity.
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Treatment |
Fever should not necessarily be treated. Fever is an important signal that there's something wrong in the body, and it can be used for follow-up. Moreover, not all fevers are of infectious origin.
Even when treatment is not indicated, however, febrile patients are generally advised to keep themselves adequately hydrated, as the dehydration produced by a mild fever can be more dangerous than the fever itself. Water is generally used for this purpose, but there is always a small risk of hyponatremia if the patient drinks too much water. For this reason, some patients drink sports drinks or products designed specifically for this purpose.
Most people take medication against fever because the symptoms cause discomfort. Fever increases heart rate and metabolism, thus potentially putting an additional strain on elderly patients, patients with heart disease, etc. This may even cause delirium. Therefore, potential benefits must be weighed against risks in these patients. In any case, fever must be brought under control in instances when fever escalates to hyperpyrexia and tissue damage is imminent.
Treatment of fever should be based primarily on lowering the setpoint, but facilitating heat loss may also contribute. The former is accomplished with antipyretics. Wet cloth or pads are also used for treatment, and applied to the forehead. Heat loss may be an effect of (possibly a combination of) heat conduction, convection, radiation or evaporation (sweating, perspiration). This may be particularly important in babies, where drugs should be avoided. However, if water that is too cold is used, it induces vasoconstriction and prevents adequate heat loss.
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