Intracranial volume-pressure relationship following thiopental or etomidate

A series of infusions of mock cerebrospinal fluid (CSF) was used to determine intracranial volume-pressure relationships in 18 anesthetized dogs. Measures of intracranial volume-pressure relationships included 1) CSF pressure prior to volume infusion (P0), 2) peak CSF pressure (Pp) caused by volume injection, 3) intracranial compliance (C, calculated as the ratio of change of intracranial volume [delta V] to change of CSF pressure [delta P]), 4) the volume-pressure response (VPR, a measure of elastance, calculated as the ratio of delta P to delta V), 5) the pressure volume index (PVI, calculated as the ratio of delta V to log Pp/P0), and 6) estimated intracranial compliance (Ce, calculated from PVI as 0.4343 PVI/P0). Six of the 18 dogs (time controls) were studied during halothane (0.4%, end expired) and nitrous oxide (66%) in oxygen, six dogs were studied prior to and following each of two doses of thiopental (approximate cumulative doses were 10.5 and 25.5 mg/kg), and six dogs were studied prior to and following each of two doses of etomidate (approximate cumulative doses were 1.52 and 3.70 mg/kg). In the time controls P0, Pp, C, VPR, PVI, and Ce were steady throughout the experimental period. Thiopental decreased P0 (by 2-3 +/- 1 cmH2O) and Pp (by 2-4 +/- 2 cmH2O), increased Ce (by 0.02-0.03 +/- 0.01 ml/cmH2O), and did not change C, VPR, or PVI. Etomidate decreased P0 (by 3-4 +/- 1 cmH2O) and Pp (by 4-6 +/- 2 cmH2O), increased Ce (by 0.03-0.04 +/- 0.01 ml/cmH2O) and did not change C, VPR, or PVI.(ABSTRACT TRUNCATED AT 250 WORDS)