Fever

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Chapter 13 Fever

Jeffrey R. Avner, MD

1 What percentage of visits to the emergency department (ED) is for the evaluation of fever?

Fever is one of the most common presenting symptoms at the pediatric ED, representing 15–30% of all visits. During the first 2 years of life, a child typically has 4–6 episodes of febrile illness.

2 What temperature is considered normal?

There is no single value that represents a “normal” temperature. This is largely because normal body temperature varies with age, time of day, physical activity, and environmental conditions. This individual variability limits the application of mean body temperature values derived from population studies. Thus, no single temperature should be used as the upper limit of normal. Rather, normal temperature is best described as a range of values for each individual. Although only a rough guide, some consider abnormal temperature to be >38.0–38.2°C (rectally) in an infant and 37.2–37.7°C (orally) in an older child or adult.

3 Who is credited with the first systematic measurement of body temperature?

In the 1860s, German physician Carl Wunderlich used foot-long thermometers to record over 1 million axillary temperature readings from 25,000 patients. He identified 37.0°C (98.6°F) as the mean temperature of healthy adults.

4 Does body temperature vary during the day?

The variation of body temperature in typical circadian rhythm becomes established by 2 years of age. Peak temperature typically occurs in late afternoon (5:00–7:00 pm), and the trough occurs in early morning (2:00–6:00 am). Daily temperature variation ranges from 0.1°C–1.3°C.

5 How does the body produce fever?

During infection, exogenous pyrogens (microbial products such as endotoxins) produced by various infectious organisms act on host inflammatory cells (especially monocytes and macrophages) to produce numerous cytokines, including endogenous pyrogens (interleukin, tumor necrosis factor, interferon). These circulating pyrogens act on the preoptic area of the anterior hypothalamus, which produces prostaglandin E2 and causes fever.

6 Where is the core body temperature set?

Core body temperature is set in the anterior hypothalamus. Variation in body temperature is detected by thermosensitive neurons in the preoptic nucleus, which then directs autonomic changes in sweat glands, blood vessels, somatic neurons, and skeletal muscles.

7 How does the body regulate temperature?

Thermoregulation is controlled by a variety of physiologic and behavioral mechanisms under the direction of the hypothalamus. Elevation of body temperature occurs primarily through metabolic activity associated with increased cell metabolism, increased muscle activity, and involuntary shivering. Body temperature is decreased primarily through vasodilatation, which thereby increases heat loss by conduction, convection, or radiation through the skin. In addition, sweating and cold preference behavior (e.g., removing clothes) help dissipate the heat.

8 Is fever beneficial or harmful?

Whether fever is friend or foe is a question for the ages. Fever has some physiologic benefits for the host, including an enhancement of both cellular and humoral immune responses as well as direct antimicrobial activity. On the other hand, fever makes the child uncomfortable and leads to a significant increase in metabolic activity (about 10% per degree Centigrade), which increases oxygen consumption, carbon dioxide production, and insensible water loss. Whether the benefits outweigh the metabolic costs is debatable. Regardless, the presence of fever alerts the parents and clinicians that the child is in the process of fighting disease and, as such, can serve as an invaluable diagnostic aid.

9 What is “fever phobia”?

Barton Schmitt coined the term in the early 1980s in reference to parents’ excessive concern about low-grade fever. Nowadays, the term fever phobia is often used to describe heightened anxiety about the presence of fever in the child that can lead to unnecessary ED visits, laboratory testing, or empiric antibiotic treatment. Of note, both parents and providers may have “fever phobia.”

Corneli HM. Beyond the fear of fever. Clin Ped Emerg Med 1:94–101, 2000.

Crocetti M, Moghbeli N, Serwint J: Fever phobia revisited: Have parental misconceptions about fever changed in 20 years? Pediatrics 107:1241–1246, 2001.

Poirer MP, Davis PH, Gonzalez-Del Rey JA, et al: Pediatric emergency department nurses’ perspectives on fever in children. Pediatr Emerg Care 16:9–12, 2000.

Schmitt BD: Fever phobia: Misconceptions of parents about fevers. Am J Dis Child 134:176–181, 1980.

10 What are the normal increases in heart rate and respiratory rate with each degree rise in body temperature?

Fever is associated with an increase in heart rate of about 10 to 15 beats per minute and an increase in respiratory rate of about 3 to 5 breaths per minute for each rise in degree Centigrade.

11 Does bundling cause fever in infants?

Overbundling of young infants, especially during the summer months, is known to increase measured temperatures. If an infant is heavily bundled or in a particularly hot environment, a 30- to 60-minute period of equilibration should be followed by a repeat temperature determination. This issue is particularly important in the evaluation of young febrile infants because the height of the fever by itself is often a determinant for proceeding with an evaluation for sepsis.

12 What are the differences in measurement among rectal, oral, and axillary temperature readings?

The core body temperature is best measured with an esophageal or nasopharyngeal probe, but this is difficult in the setting of an ED. Therefore, rectal temperature is used as the standard measurement to indirectly measure core body temperature. Oral measurement in the sublingual pocket is estimated to be 0.5–1°C lower than rectal temperature. Axillary temperatures are imprecise, inaccurate, and insensitive and therefore of limited value.

Craig JV, Lancaster GA, Williamson PR, et al: Temperature measured at the axilla compared with rectum in children and young people: Systemic review. BMJ 320:1174–1178, 2000.

13 Does otitis media increase tympanic membrane temperature?

Infrared tympanic thermometry is a popular method used in EDs, and recent studies show that, at least in older children and adults, the results are reasonably accurate. Otitis media has been shown to increase tympanic temperatures only slightly, by about 0.4°C. Interestingly, although nonobstructive cerumen does not affect tympanic thermometry, cerumen that completely obstructs the ear canal leads to underestimation of temperature.

Kelly B, Alexander D: Effect of otitis media on infrared tympanic thermometry. Clin Pediatr 30:46–48, 1991.

14 Can parents detect fever subjectively?

When parents say that their child is “burning up” with fever, they are usually correct. In general, parents are both moderately sensitive (75–85%) and specific (75–85%) in detecting the presence of fever subjectively in children. However, they may not be as accurate in estimating the height of fever. In young infants (less than 2 months old), when the height of the fever is crucial for determining management, always obtain a rectal temperature.

Hooker EA, Smith SW, Miles T, et al: Subjective assessment of fever by parents: Comparison with measurement by noncontact tympanic thermometer and calibrated rectal glass mercury thermometer. Ann Emerg Med 28:313–317, 1996.

15 When sponging a child for treatment of fever, what is the best temperature for the water?

The value of sponging to decrease temperature is controversial. Sponging uses evaporation to help cool the child. Sponging can be used in combination with an antipyretic and may take up to 20 minutes to be effective. Use tepid or lukewarm water so that the child remains comfortable and does not shiver. Never use cold water or isopropyl alcohol, as they cause excessive vasoconstriction and shivering. In addition, isopropyl alcohol can be toxic through skin absorption.

16 What did Hippocrates feel was the role of fever?

Hippocrates, the father of medicine, felt that fever helped balance the four humors (blood, yellow bile, black bile, and phlegm), which were believed to cause disease when out of balance. At the current time, this theory remains unproven!

17 Does high fever cause brain damage?

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