Fever

Pathogenesis: The hypothalamic set point increases, causing peripheral vasoconstriction (i.e., heat conservation). The pt feels cold as a result of blood shunting to the internal organs. Mechanisms of heat production (e.g., shivering, increased hepatic thermogenesis) help to raise the body temperature to the new set point. Increases in peripheral prostaglandin E₂ account for the nonspecific myalgias and arthralgias that often accompany fever. When the set point is lowered again by resolution or treatment of fever, processes of heat loss (e.g., peripheral vasodilation and sweating) commence.
Etiology: Most fevers are associated with self-limited infections (usually viral) and have causes that are easily identified.

APPROACH TO THE PATIENT
Fever History: A meticulous history is essential, with particular attention to the chronology of events (e.g., in the case of rash: the site of onset and the direction and rate of spread; see below) and the relation of symptoms to medications, pet exposure, sick contacts, sexual contacts, travel, trauma, and the presence of prosthetic materials. Physical examination: A thorough physical examination should be performed. A consistent site for taking temperatures should be used. Temperature-pulse dissociations (relative bradycardia) should be noted if present (sometimes present, for example, with typhoid fever, brucellosis, leptospirosis, factitious fever). Close attention should be paid to any rash, with precise definition of its salient features. Lesion type (e.g., macule, papule, nodule, vesicle, pustule, purpura, ulcer; see Chap. 60 General Examination of the Skin for details), configuration (e.g., annular or target), arrangement, and distribution (e.g., central or peripheral) Classification of rash Centrally distributed maculopapular eruptions (e.g., viral exanthems, exanthematous drug-induced eruptions) Peripheral eruptions (e.g., Rocky Mountain spotted fever, secondary syphilis, bacterial endocarditis) Confluent desquamative erythemas (e.g., toxic shock syndrome) Vesiculobullous eruptions (e.g., varicella, primary HSV infection, ecthyma gangrenosum) Urticaria-like eruptions: In the presence of fever, usually due to urticarial vasculitis caused by serum sickness, connective-tissue disease, infection (hepatitis B virus, enteroviral, or parasitic infection), or malignancy (particularly lymphoma) Nodular eruptions (e.g., disseminated fungal infection, erythema nodosum, Sweet's syndrome) Purpuric eruptions (e.g., meningococcemia, viral hemorrhagic fever, disseminated gonococcemia) Eruptions with ulcers or eschars (e.g., rickettsial diseases, tularemia, anthrax) Laboratory tests: CBC with differential, ESR, and C-reactive protein; other tests as indicated by history and physical examination

TREATMENT
Fever The use of antipyretics is not contraindicated in common viral or bacterial infections and can relieve symptoms without slowing resolution of infection. Withholding of antipyretics may be useful, however, in evaluating the effectiveness of a particular antibiotic or in diagnosing conditions with temperature-pulse dissociations or relapsing fevers (e.g., infection with Plasmodium or Borrelia species). Treatment of fever in pts with preexisting impairment of cardiac, pulmonary, or CNS function is recommended to reduce oxygen demand. Aspirin, NSAIDs, and glucocorticoids are effective antipyretics. Acetaminophen is preferred because it does not mask signs of inflammation, does not impair platelet function, and is not associated with Reye's syndrome. Hyperpyretic pts should be treated with cooling blankets in addition to oral antipyretics.

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Fever

Fever

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