Intracranial pressure during nifedipine-induced hypotension

The effect of nifedipine-induced hypotension on intracranial pressure (ICP) was investigated in cats with normal and artificially increased ICP. Eleven cats were anesthetized with intraperitoneal pentobarbital (25 mg/kg), intubated, and ventilated with nitrous oxide in oxygen. Mean arterial pressure (MAP), heart rate (HR), and mean pulmonary artery pressure (PAP) were continuously recorded. A double 19 gauge needle was inserted into the cisterna magna; ICP was continuously monitored from one needle and the other was used to increase and maintain ICP at 27 ± 4 mm Hg by infusion of pH-adjusted Ringer's lactate solution. After control measurements were taken, nifedipine was given intravenously in each cat when ICP was normal and increased. Infusion of 96 ± 12 μg (SEM) nifedipine (≃ 33 μg/kg) reduced MAP 35-45% for 2.5 ± 0.8 min when ICP was normal, and for 2.0 ± 0.6 min when ICP had been increased. When initial ICP was normal, nifedipine-induced hypotension produced a small (2.2 mm Hg) but statistically significant increase in ICP and decrease in cerebral perfusion pressure (P < 0.01). When ICP was initially elevated, nifedipine-induced hypotension produced a larger increase in ICP (5 ± 1 mm Hg) and a proportionately larger decrease in cerebral perfusion pressure (P < 0.01).