25. Fever – definition, etiology and pathogenesis. Significance of fever. Stages of fever. Changes in metabolism in fever. Alterations in the function of organs and systems.

FEVER - DEFINITION, ETIOLOGY, AND PATHOGENESIS. SIGNIFICANCE OF FEVER. STAGES OF FEVER. CHANGES IN METABOLISM IN FEVER. CHANGES IN THE FUNCTION OF ORGANS AND SYSTEMS

• ⭐ Fever (pyrexia) - an elevation in body temperature that is caused by a temporary reorganisation of the set point in the hypothalamic thermoregulatory centre
• Fever is resolved when the factor that caused the increase in the set point is removed

Degrees of fever

1. Subfebrile - up to 38
2. Moderately high - up to 39
3. High - 39-40
4. Hyperpyretic - above 40

Etiology of fever

• Fever is caused by pyrogens

1. Exogenous pyrogens
2. a) Bacterial - lipopolysaccharide toxin produced by gram negative bacteria
3. b) Non-bacterial - toxic elements (lead), synthetic hormones, hypertonic saline
4. Endogenous pyrogens - IL-1, alpha-interferon, TNF-alpha, PGE2

• ❏ Exogenous pyrogens act indirectly by inducing the production of endogenous pyrogens, which act directly on the thermoregulatory centre
• ❏ Endogenous pyrogens are thought to increase the set point through the action of prostaglandin E2
• ❏ Neurogenic fever - a fever that has its origin in the CNS and is usually caused by damage to the hypothalamus caused by trauma, bleeding, or an increase in intracranial pressure
• Neurogenic fevers are characterised by a high temperature that is resistant to antipyretic therapy and is not associated with sweating