Cerebrovascular adaptation to prolonged halothane anesthesia is not related to cerebrospinal fluid pH

The purpose of this study was to evaluate the time-dependent effects of steady-state halothane anesthesia on cerebrovascular variables and their relationship to cerebrospinal fluid (CSF) pH. Eight mongrel dogs underwent a 7-h anesthetic, receiving halothane (1.0% end-tidal), O2 (50%), and balance N2. Cerebral blood flow (CBF) was measured by injection of radioactively labeled microspheres. CSF was sampled from the cisterna magna and cerebral venous blood from the superior sagittal sinus. Measurements were made at 2 h postinduction and hourly for 5 h thereafter. Total CBF at 2 h postinduction was 148 +/- 36 ml X 100 g-1 X min-1 and showed a significant decay over the subsequent 5 h to 70 +/- 3 ml X 100 g-1 X min-1. Regional variations were noted, those areas with highest initial flows showing both a greater relative and absolute reduction in flow. Cerebral vascular resistance increased significantly (39%), as did mean arterial pressure (15%). CSF pH values remained constant throughout the experiment. Arterial blood acid-base physiology was also unchanged. Sagittal sinus PCO2 increased significantly from 43 +/- 4 to 49 +/- 3 mmHg while sagittal sinus pH decreased from 7.31 +/- 0.01 to 7.37 +/- 0.02, consistent with the normalization of CBF. Cerebral metabolic oxygen consumption did not change significantly. The authors conclude that time-dependent changes in cerebrovascular parameters under prolonged steady-state halothane anesthesia are not due to changes in CSF pH and thus brain extracellular acid-base chemistry.