Fever

Body Temperature Regulation

Body temperature affects all biochemical processes and is controlled by the thermoregulatory center in the hypothalamus. The thermostatic set point is the level at which body temperature is maintained. When temperature rises above the set point, heat dissipation mechanisms are activated, while heat production mechanisms are activated when temperature drops below the set point.

Definition & Purpose

Fever is defined as the elevation of body temperature due to the upward displacement of the hypothalamic set point caused by cytokines. The exact mechanisms of fever remain not fully understood. The purpose of fever includes signaling the presence of infection, enhancing immune function with small temperature elevations, and inhibiting the growth of many microorganisms. Fever can also be triggered by non-infectious conditions such as cancer, medication, or neurogenic fever resulting from head injuries.

Causes of Fever

Fever is induced by pyrogens, which can be categorized into exogenous pyrogens, acting indirectly and taking hours to cause fever, and endogenous pyrogens, released directly from cells such as leukocytes and macrophages, which increase the hypothalamic set point through prostaglandins.

Mechanism of Fever

The key processes involved in fever include the release of PGE2 or cytokines from inflammatory cells, the resetting of the thermostatic set point, and the activation of temperature-raising responses like vasoconstriction, shivering, piloerection, and increased metabolism. Once the core body temperature reaches the new set point, temperature-reducing responses such as vasodilation, sweating, and increased ventilation occur.

The Course of Fever

Fever develops in several phases, starting with a prolonged temperature rise and the establishment of a new high, where the body feels warm. Treatments may involve the removal of pyrogens through various methods. The return to normal temperature is marked by body responses promoting heat loss, such as sweating and vasodilation.

Clinical Course of Fever (4 Stages)

The clinical course of fever consists of four stages: the prodromal period, where temperature starts to rise along with chills and non-specific complaints; the chill stage, characterized by shivering, vasoconstriction, and piloerection, leading to a warm sensation once the set point is reached; the flush stage, where cutaneous vasodilation occurs and the skin becomes warm and reddened; and defervescence, which involves the return of temperature to normal, marked by sweating.

Manifestations of Fever

Common symptoms associated with fever include anorexia, muscle and joint pain, fatigue, increased respiration and heart rate, dehydration due to sweating and vapor loss, and an increased metabolic rate. Additionally, headache can occur due to cerebral vessel vasodilation. There are special considerations for the elderly, as delirium and confusion may arise from poor oxygenation and cerebral hypoxemia.

Management of Fever

General management strategies for fever involve treating the underlying cause, using cool sponge baths and cooling blankets, ensuring adequate fluid intake along with simple carbohydrates, and administering antipyretic medications.

Fever in Children

Fever is common in children, particularly in infants and young children (ages 1 day to 3 years). A fever is defined as a rectal temperature of 38 degrees Celsius or more, with common causes including respiratory, gastrointestinal, urinary tract infections, and central nervous system issues. Emergency signs that may necessitate hospitalization include lethargy, poor feeding, hypoventilation, or cyanosis, which may warrant a septic work-up with additional tests.

Fever in the Elderly

Concerns arise in the elderly, as slight temperature elevations are significant due to usually lower baseline temperatures, with a fever considered at an elevation of at least 1.1°C. Reasons for altered responses to fever include changes in hypothalamic function and pyrogen release, as well as reduced responses to produce heat like vasoconstriction and shivering. Manifestations can include changes in functional capacity, mental status deterioration, weakness, fatigue, and weight loss.