Intracranial pressure during hypotension and subsequent vasopressor therapy in anesthetized cats

The effects of vasopressor therapy on intracranial pressure (ICP) during hypotension were evaluated in 45 adult cats anesthetized with pentobarbital and hyperventilated via an endotracheal tube with nitrous oxide, 70 per cent, and oxygen, 30 per cent, to maintain Paco2 25 plus or minus 5 torr. Hypotension was induced by intravenous administration of trimethaphan camsylate or sodium nitroferricyanide and by hemorrhage. Vasopressor (norepinephrine, ephedrine, or isoproterenol) administration in the absence of hypotension caused slight transient increases in ICP. Trimethaphan produced increases in ICP averaging 4.3 mm Hg, while sodium nitroferricyanide caused no change and hemorrhage decreased ICP by 3.9 mm Hg. After hypotension was established, vasopressors caused increases in ICP of 1-21 mm Hg. The greatest increase was seen with norepinephrine administration during sodium nitroferricyanide-induced hypotension. Increases in ICP were pronounced in absolute magnitude and rapidity of rise but were of short duration (2 to 5 minutes). The elevation of pressure might be of clinical significance in patients who have pre-existing intracranial hypertension or space-occupying lesions.