Fever: Nursing

A fever is an abnormal increase in body temperature, and it’s part of a biologic response controlled by the central nervous system through thermoregulation.

Normally, the average body temperature should be between 36.4 and 37.5°C, or 97.5 and 99.5°F, and it can vary due to numerous factors, including the time of day, activity, age, and the phase of the menstrual cycle.

Now, let’s review the physiology of thermoregulation. The internal body temperature is maintained by the hypothalamus, which is a small part of the forebrain located just below the thalamus.

So, when there is an increase in body temperature, the hypothalamus initiates heat dissipation mechanisms to reduce it, such as vasodilation of blood vessels near the skin, and increased sweat production by sweat glands.

Meanwhile, heat production can occur as a result of metabolic processes that generate heat as a byproduct, even while at rest or during voluntary movement. Also, when the body needs to warm up, the hypothalamus initiates the cold stress response which includes involuntary shivering.

Another contributing factor can be an increased release of the thyroid hormone, called thyroxine, which increases metabolism and in turn body temperature. In addition, neonates rely on nonshivering thermogenesis, which utilizes brown adipose tissue, a special type of fat that usually disappears after infancy.

Lastly, sympathetic stimulation helps avoid heat dissipation by triggering vasoconstriction of blood vessels on the skin, as well as piloerection, meaning erection of hairs due to contraction of the arrector pili muscles, creating an insulating layer.

Most commonly, a fever is caused by an underlying infection. Fever can also occur because of inflammation in absence of an infection. This can also happen with hypersensitivity reactions in response to a medication like penicillin; malignant conditions like lymphoma; and chronic inflammatory conditions like inflammatory bowel disease, Kawasaki disease, or autoimmune diseases like lupus.

Now let’s look at the pathology of fever. Most often, a fever is triggered by either endogenous pyrogens or exogenous pyrogens. Endogenous pyrogens are proinflammatory molecules from inside the body, like interleukin 1, tumor necrosis factor or TNF, and interferon; as well as prostaglandins.

Exogenous pyrogens, on the other hand, refer to substances from outside the body, like an infectious pathogen, which trigger the production of proinflammatory molecules.

Regardless of whether the trigger is exogenous or endogenous, the end result is that the proinflammatory molecules reach the hypothalamus, and alter the hypothalamic thermoregulatory center.

Consequently, the hypothalamus employs the mechanisms used to generate heat, like shivering and an increased metabolism. At the same time, heat loss is decreased through peripheral vasoconstriction. Ultimately, these mechanisms come together to increase the body temperature to an elevated set-point, leading to the development of a fever.

The increased temperature enhances parts of the immune response, like increasing neutrophil and T-cell production while simultaneously slowing the pathogen’s growth. In response to the fever, the body typically produces natural antipyretics, called cryogens, which helps to prevent fevers from rising to a possibly lethal level at 41°C or 106°F.

On a side note, fever should be distinguished from hyperthermia, which has a different pathogenesis. In hyperthermia, thermoregulation fails due to causes such as extreme environmental heat or certain drugs, and the temperature can then rise unopposed to lethal levels.1 C