Dose-related changes in the rate of cerebrospinal fluid formation and resistance to reabsorption of cerebrospinal fluid following administration of thiopental, midazolam, and etomidate in dogs.

Abstract

The rate of cerebrospinal fluid (CSF) formation (Vf) and resistance to reabsorption of CSF (Ra) were determined in dogs at four doses of thiopental (6, 12, 18, and 24 mg.kg-1.h-1), midazolam (0.5, 1.0, 1.5, and 2.0 mg.kg-1.h-1), and etomidate (0.86, 1.72, 2.58, and 3.44 mg.kg-1.h-1). Results were compared within and between groups and to previously reported normal values for Vf (0.030-0.054 ml/min) and Ra (220-240 cmH2O.ml-1.min) in dogs. At the two lower doses of thiopental, midazolam, or etomidate Vf was not significantly different than previously reported normal values. At the two higher doses of each drug Vf was 0.019-0.024 ml/min, significantly reduced compared to Vf at the two lower doses of each drug. The pattern of Ra data was more varied. With thiopental Ra was elevated at the lowest dose, (354 +/- 17 cmH2O.ml-1.min, mean +/- SD) reduced at the highest dose (156 +/- 19 cmH2O.ml-1.min), and not significantly different than previously reported normal values at the two intermediate doses. With midazolam Ra was elevated at the lowest and highest doses (332 +/- 25 and 378 +/- 18 cmH2O.ml-1.min) and normal at the two intermediate doses. With etomidate Ra was normal at the three lower doses and reduced at the highest dose (187 +/- 13 cmH2O.ml-1.min). It is concluded that CSF volume may be increased and the CSF pressure at which CSF volume contracts may be increased by doses of thiopental or midazolam that increase Ra, but not increased by etomidate.