Dr. Erice Calvo-Sotelo is a recognized specialist in Internal Medicine, being an expert in infectious diseases and in infection on joint prostheses and osteoarticular infection. He is currently Head of the Department of Internal Medicine at the Asepeyo Hospital in Madrid, and author of numerous publications. For many years he has combined his professional work with teaching abroad.
Body temperature is controlled by the thermoregulatory center of the hypothalamus, a structure located in the brain. Nerve cells in the hypothalamus receive information about skin temperature from peripheral nerves and body temperature from the blood and integrate this information to maintain a normal body temperature (36.5oC – 37oC).
How does fever occur?
Fever occurs as a result of the release of substances in the body that “reset” the thermoregulatory center upwards, whereby a series of adjustments take place that increase the temperature and conserve body heat. The production of these pyrogenic substances (with the consequent appearance of fever) occurs in many diseases: infections, inflammatory processes, autoimmune processes, tumors, etc. Infections are the most frequent cause of fever in the general population.
Normal values for body temperature have been established by studies in healthy persons whose oral temperature has been taken; from these studies, fever has been defined as a morning temperature above 37.2oC and an evening temperature above 37.7oC. However, in colloquial terms we speak of “tenths” from 37oC and fever from 37.5oC – 38oC. The term hyperthermia is reserved for very high fever (above 41.5oC); hyperpyrexia (heat stroke) refers to an uncontrolled rise in body temperature that exceeds the body’s ability to lose heat and in which the thermoregulatory center does not intervene.
How to measure body temperature?
Body temperature can be measured in the mouth, ear canal, axilla or rectum. Generally, axillary temperature is similar to oral temperature, rectal temperature is 0.4oC higher than oral temperature and ear canal temperature is highly variable. Axillary temperature is most often used; ear thermometers are convenient and quick but are usually more expensive.
Which antipyretics to take and to what extent?
Antipyretics act on the thermoregulatory center to bring it back to normal. Acetylsalicylic acid, nonsteroidal anti-inflammatory drugs (NSAIDs) and acetaminophen have antipyretic action. NSAIDs and acetylsalicylic acid produce gastric irritation and alter platelets; in children with virus infections, acetylsalicylic acid increases the risk of Reye’s syndrome. Therefore, acetaminophen is the drug of choice to treat fever.
As antipyretics do not worsen or improve febrile processes but help the patient to feel better, it is advisable to use them when fever is present. To avoid the symptoms that accompany the rise and fall of temperature (general malaise, chills, shivering, sweating), it is preferable to administer paracetamol on a regular basis (i.e. every 6-8 hours) instead of taking it only when the fever rises. In hyperthermia, in addition to an antipyretic, cold compresses or warm-cold water baths can be used to help reduce fever. It is essential not to exceed the maximum recommended daily dose of paracetamol (80 mg per kg in children; 4 grams in adults), otherwise very serious acute liver damage may occur. As always with any illness, it is important to consult a physician.