Overview
Fever is defined as a body temperature higher than the normal core temperature of 100°F (37.8°C). It is a sign of a regulated increase in the body’s thermoregulatory set point in response to a pyrogen. Fever is differentiated from hyperthermia, which represents a malfunctioning of the normal thermoregulatory process at the hypothalamic level, and hyperpyrexia, a body temperature greater than 106°F (41.1°C) that typically results in harmful mental and physical consequences.
Fever is a symptom—an indication of an underlying process. It is not inherently harmful; in fact, there is evidence that fever is an adaptive response and that elevated body temperature may be beneficial. The principal reason for treating fever is to alleviate patient discomfort. Therefore, the decision to treat fever should be based on a patient-specific risk–benefit ratio. Arguments against treating fever include the generally benign and self-limited course of fever, the possible elimination of a diagnostic or prognostic sign, the attenuation of enhanced host defenses (i.e., possible therapeutic effect of fever), and possible untoward effects of antipyretic medications.
No correlation exists between the magnitude and pattern of temperature elevation (i.e., persistent, intermittent, recurrent, or prolonged) and the principal etiology or severity of the underlying pathology. Because it is difficult to determine the cause of the fever on the sole basis of the temperature reading, investigation into the underlying cause is important. In some instances, fever may indicate a serious condition (e.g., acute infectious process) that requires prompt medical evaluation.
Etiology
- The average body temperature usually is maintained in the “set point” range, between 97.5°F and 98.9°F (36.4°C and 37.2°C).
- Normal body temperature varies throughout the day. Healthy infants ages 3–4 months typically experience the highest temperatures just before bedtime; body temperature then falls more than a degree during actual sleep. Normal body temperature in adults is higher on average in the evening than in the morning.
- An increase in body temperature may be idiopathic or can be caused by a variety of mechanisms, including an infectious process, pathologic processes, a response to certain drugs, or vigorous activity.
- Most episodes of fever are caused by microbial infections.
- Drug-induced fever is a febrile response to medication administration. It usually is possible to establish a temporal relationship between the elevation in body temperature and the administration of a medication. In addition, body temperature often remains elevated despite improvement of the underlying disorder.
Signs and Symptoms
- The most important sign of fever is an elevated body temperature. Measurements of body temperature at the rectal, axillary, oral, temporal, or ear canal sites represent estimates of core temperature (the temperature of the blood that surrounds the hypothalamus).
- A rectal temperature greater than 100.4°F (38.0°C) is considered elevated.
- An oral temperature greater than 99.7°F (37.6°C) is considered elevated.
- An axillary temperature greater than 99.3°F (37.4°C) is considered elevated.
- A tympanic temperature greater than 100.0°F (37.8°C) is considered elevated.
- A temporal temperature greater than 100.1°F (37.8°C) is considered elevated.
- A rectal temperature greater than 100.4°F (38.0°C) is considered elevated.
- Signs and symptoms that typically accompany fever and cause a great deal of discomfort include headache, diaphoresis, generalized malaise, chills, tachycardia, arthralgia, myalgia, irritability, and anorexia.
Complications
- Acute complications of fever are rare but may include seizures, dehydration, and change in mental status.
- The risk of complications is increased in infants and in patients with brain tumors or hemorrhage, central nervous system infections, preexisting neurologic damage, and decreased ability to dissipate heat.
- Older patients have a higher risk of fever-related complications because of decreased thirst perception and perspiration ability.
- The risk of complications is increased in infants and in patients with brain tumors or hemorrhage, central nervous system infections, preexisting neurologic damage, and decreased ability to dissipate heat.
- Serious complications—dehydration, delirium, seizures, coma, or irreversible neurologic or muscle damage—are associated most frequently with hyperpyrexia (temperature >106°F orally), which usually is associated with hyperthermia. Febrile patients rarely have a body temperature exceeding 106°F.
- Febrile seizures are seizures that occur in febrile infants or children who do not have an intracranial infection, a metabolic disturbance, or a history of afebrile seizures. Simple febrile seizures are most common; they are characterized by nonfocal movements and generally last <15 minutes, with only one occurrence in a 24-hour period.
- Febrile seizures occur in up to 5% of all children from the ages of 6 months to 5 years; most occur in children ages 18–24 months.
- Significant neurologic sequelae are unlikely after a single pediatric febrile seizure.
- Prophylaxis against recurrent simple febrile seizures with antiepileptic or antipyretic drugs is not recommended by the American Academy of Pediatrics.
- Febrile seizures occur in up to 5% of all children from the ages of 6 months to 5 years; most occur in children ages 18–24 months.
Treatment
- Fever exceeding 101°F (38.3°C) orally may be treated with antipyretic agents and nonpharmacologic measures.
- Treatment with antipyretics also may be indicated at lower temperatures if the patient is experiencing discomfort or is of advanced age. Older persons have been shown to have a lower average body temperature, even when ill.
- The discomfort associated with a fever <101°F (38.3°C) may be the primary indication for any of the nonprescription antipyretic medications, given that these agents are also analgesics.
General/Nonpharmacologic Treatment Measures
- Nonpharmacologic therapy consists mainly of adequate fluid intake to prevent dehydration.
- Fluid intake in febrile children should be increased by at least 30–60 mL (1–2 ounces) of fluids (e.g., sports drinks, fruit juice, water, balanced electrolyte replacement products, or ice pops) per hour.
- Fluid intake in febrile adults should be increased by at least 60–120 mL (3–4 ounces) of fluids per hour (unless contraindicated).
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- Fluid intake in febrile children should be increased by at least 30–60 mL (1–2 ounces) of fluids (e.g., sports drinks, fruit juice, water, balanced electrolyte replacement products, or ice pops) per hour.
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