Fever and intracranial pressures

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The effect of fever upon intracranial pressures was determined in the rabbit and cat. In the unanesthetized rabbit and cat, cerebrospinal fluid (CSF) pressure was measured via direct cannulation of the lateral cerebral ventricle. Intracranial pressure (ICP) was measured in the rabbit by a subarachnoid screw technique. In all cases, intravenous administration of bacterial pyrogen extracted from Salmonella abortus equi resulted in significant differences from controls in physiological variables measured during the initial “chill” phase of the fever. There was an increase in body temperature, a fall in CSF or ICP pulse rate, an increase in pulse pressure amplitude, and a small increase in mean CSF or ICP. In addition, venous and arterial blood pressures increased significantly and, consistent with heat conservation, there was a fall in respiratory rate as well as cutaneous vasoconstriction in the ears. The arterial carbon dioxide tension was unchanged during the prodome but fell significantly during the chill and flush phases and rose again during defervescence. The results suggest that in these animals there is a slight increase in pressures within the cranium during the “chill” phase of a pyrogen induced fever, resulting from changes occurring in many body systems during this phase of the fever.