The response of canine intracranial pressure to systemic hypotension induced with nitroglycerine

Changes in intracranial pressure were studied in 18 greyhounds in relation to decreases in systemic arterial pressure produced by nitroglycerine. At normal values of i.c.p. (less than 12 mm Hg) GTN produced an increase in i.c.p. of 3.1 (+/- 0.6) mm Hg (mean +/- SEM). Under conditions of increased i.c.p. (12 + mm Hg) small decreases in mean arterial pressure (m.a.p.) (less than 25% control) were associated with an increase of 4.7 (+/- 0.5) mm Hg, whereas larger decreases in m.a.p. (greater than 25% control) were associated with a decrease of 3.2 (+/- 0.9) mm Hg in i.c.p. In 11 of 19 observations in which a decrease in intracranial pressure had occurred in association with systemic hypotension there was a rebound increase in i.c.p. as m.a.p. was restored. It is suggested that i.c.p. be decreased before this drug is used to produce hypotension during neurosurgery.