CHAPTER 20 Approach to the Febrile Patient
Thermoregulation

Figure 20-1 Normal thermoregulation.
(From Miller JB: Hyperthermia and fever of unknown origin. In Ettinger SJ, Feldman EC (eds): Textbook of veterinary internal medicine, ed 6, St Louis, 2005, Saunders/Elsevier.)
Hyperthermia
Endogenous Pyrogens
In response to stimuli by an exogenous pyrogen, proteins (cytokines) released from cells of the immune system trigger the febrile response. Macrophages are the primary immune cell involved, although T and B lymphocytes and other leukocytes may play significant roles. The proteins produced are called endogenous pyrogens or fever-producing cytokines. Although interleukin-1 (IL-1) is considered the most important cytokine, at least 11 cytokines capable of initiating febrile responses have been identified (Table 20-1). Some neoplastic cells are also capable of producing cytokines that lead to a febrile response. The cytokines travel via the blood stream to the AH, where they bind to the vascular endothelial cells within the AH and stimulate release of prostaglandins (PGs), primarily prostaglandin E2 (PGE2) and possibly prostaglandin E2α(PGE2α). The set point is raised, and the core body temperature increases through increased heat production and conservation (Figure 20-2).
TABLE 20-1 Proteins with pyrogenic activity
Endogenous pyrogen | Principal source |
---|---|
Cachectin/tumor necrosis factor (TNF-α) | Macrophages |
Lymphotoxin/tumor necrosis | Lymphocytes (T and B) factor-β (TNF-β; LT) |
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