Abstract
Fever is one of the most recognizable symptoms of illness and is responsible for 15-30% of all Emergency Department and Urgent Care visits in pediatrics. Children have as many as 4-6 febrile illness during the first two years of life and many of these febrile episodes have no clear source of infection. Parents are often concerned that fever, especially high fever, can cause serious complications including brain damage and thus view fever as a “dangerous” symptom. This perception is the cornerstone of “fever phobia”, an exaggerated fear of fever, which can cause parental worries and fears eventually leading to visits to health care providers and pressure to prescribe antibiotics. Therefore, an evidence-based understanding of the pathophysiology of fever and use of antipyretics are essential for any Emergency Department of Urgent Care provider who cares for children. This chapter answers many common questions about fever and highlights the myths and facts about etiology and management.
Keywords
antipyretic, bacteremia, fever, hyperthermia
1
What causes fever?
The body has a “central thermostat” comprised of a specialized group of neurons in the hypothalamus that act to maintain the body at a physiologic “set point.” This set point changes when pyrogens (endogenous or exogenous substances that produce fever) stimulate an inflammatory response that increases the production of prostaglandin E, which in turn acts on the hypothalamus to raise the set point. When the body’s temperature is lower than the set point, various mechanisms are employed to increase heat production and raise the body’s temperature to be in balance with the new set point, resulting in fever.
2
What are the different phases of the febrile response?
The first phase of the febrile response is the “chill” phase. Various mechanisms, including increasing cellular metabolism, increasing skeletal muscle activity through involuntary shivering, peripheral vasoconstriction, and seeking a warmer environment are employed in order to raise the body’s temperature to a new set point. The “flush” phase occurs as the set point is lowered back toward normal body temperature with illness resolution or administration of antipyretics. This phase is characterized by peripheral vasodilation, sweating, and seeking a cooler environment as the body seeks to lower its temperature to the new set point.
3
Is there a difference between fever and hyperthermia?
Yes, fever is a physiologic response, and hyperthermia is not. Fever is an elevation of body temperature that is regulated by the body’s internal thermoregulatory center in the hypothalamus, whereas hyperthermia represents elevation of body temperature due to an external environmental source, with no input from the body’s thermoregulatory center. Temperature elevation secondary to hyperthermia is dangerous as the thermoregulatory center does not stimulate vasodilation and sweating to lower the temperature, as it would in the case of fever.
4
Is normal body temperature 98.6°F (37°C)?
There is no single normal value for body temperature. Rather, there is a range of normal that can vary in each person by as much as 0.5°C from the mean, based on various factors. These include time of day (lowest in the morning and highest in the evening), age (higher in infants), sex, physical activity, and ambient temperature.
5
So where did the value 98.6°F come from?
The value 98.6°F is attributed to Carl Wunderlich, who published, in 1868, a study in which he used a foot-long axillary thermometer to take 1 million temperature readings in more than 25,000 patients and found 98.6°F to be the mean temperature; hardly accurate by today’s standards.
6
Which method of temperature measurement is most reliable (axillary, oral, rectal, tympanic) or does it not really matter?
Table 12.1 compares the different methods of temperature measurement. As each have pros and cons, it is most important to use a consistent form of measurement to monitor changes in body temperature. Keep in mind these methods measure body temperature at a peripheral site, which lags behind the core body temperature.
| Method | Pros | Cons | Normal range, mean °C (°F) | Fever °C (°F) |
|---|---|---|---|---|
| Axilla | Comfortable Safe | Lag time Inaccurate during chill phase and skin cooling from sweating | 34.7–37.3, 36.4 (94.5–99.1, 97.5) | 37.4 (99.3) |
| Oral (sublingual) | Comfortable (children >5) Safe Less lag time More accurate | May be affected by recently consumed fluids or evaporative effects of mouth breathing | 35.5–37.5, 36.6 (95.9–99.5, 97.9) | 37.6 (99.7) |
| Rectal | Safe Closest to core temperature Not affected by environmental factors | Less comfortable Concern for cross-contamination if standard precautions aren’t followed | 36.6–37.9, 37.0 (97.9–100.2, 98.6) | 38.0 (100.4) |
| Tympanic | Comfortable Safe Cost effective | Difficult to aim thermometer at TM Cerumen may block TM | 35.7–37.5 (96.3–99.5, 97.9) | 37.6 (99.7) |
| Temporal | Comfortable Safe | Low diagnostic accuracy | 36.4–37.7 (97.5–99.9) | 37.8 (100.0) |
7
Can children have fever even if they don’t have an elevated body temperature?
When children are in the “chill” phase of fever, their body temperature may not be elevated, as the core body temperature may not have reached the thermoregulatory center’s new set point. However, children may manifest symptoms of the febrile response such as shivering, cool skin, tachycardia, tachypnea, and decreased appetite. Fever will likely occur 20–30 minutes after the development of these systemic symptoms.
8
Is it “feed a cold and starve a fever” or the other way around?
Although generally dismissed as folklore, there may be some physiologic explanation for this classic proverb, which dates back to the 1500s. Studies show that food intake upregulates cell-mediated immunity (via increased interferon-gamma production) that can help fight viral infections such as colds, while withholding food increases humoral immunity (via upregulation of IL-4), which is helpful in fighting bacterial infections, historically thought to be the predominant cause of fever.
9
Is there a value that is considered a “high” fever (or how high is too high)?
There is no specific value considered too “high” for a fever (as opposed to hyperthermia). Fever increases a child’s metabolic rate and catabolism, making him or her more prone to heat loss. Most healthy children can accommodate these stresses through normal physiologic processes; however, children with chronic illnesses and those who are immunosuppressed or have cardiopulmonary disease may not be able to adjust to this increased demand and are at higher risk for systemic effects.
10
Does the height of fever predict the risk of serious bacterial illness (SBI) or mortality?
While the presence of fever is usually indicative of an ongoing infectious process, the height of the temperature is not an accurate marker of SBI or mortality in otherwise healthy children. Thus, the height of fever has limited use in determining management; other clinical features, especially the child’s clinical appearance, are better predictors.
11
Do parents pay too much attention to taking their child’s temperature?
Parents often exhibit “fever phobia,” displaying excessive concern about fever and its potential effects on their child with heightened concern at higher temperatures. This often leads to frequently taking the child’s temperature. It is important to educate parents that fever is a symptom of their child’s illness that will persist until the underlying illness has resolved. Fever itself is not dangerous to an otherwise healthy child, and the specific temperature value is generally not important.
12
Should I make the parents focus on preventing fever in their child?
Trying to prevent or “control” fever is generally futile and will likely increase fever phobia. Parents should be directed to focus on the child’s comfort and clinical appearance until the resolution of the underlying illness. Antipyretics can be used for comfort. A change in clinical appearance should prompt reassessment by a health care provider.
13
Does high fever cause brain damage or death?
There is no evidence that high fever itself causes brain damage or death, even with temperatures as high as 107.6°F (42°C). Although excessive heat (>107°F) may denature proteins in vitro, fever likely affects protein expression, allowing them to adapt to high temperature in vivo. Nevertheless, over 25% of parents believe fever causes brain damage.
14
Can I trust parents who say their child is “burning up”?
Parents’ tactile assessment of their child’s fever has a high sensitivity (80%–90%), but its specificity is much lower (about 50%), suggesting that parents’ assessment is more reliable at ruling out a fever, rather than ruling one in.
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