The dynamics of systemic and hepatic circulation of 54 dogs were investigated both during and after anesthesia with halothane plus 60% nitrous oxide (GOF) and halothane plus 60% nitrogen (OF). To examine the effects of nitrous oxide, the systemic and hepatic circulation dynamics of GOF and OF anesthesia were compared at the same halothane concentration (1.5%) and minimum alveolar concentration (1 and 2 MAC) in both procedures. There were no significant differences in the dynamics of GOF and OF at 1.5% halothane concentration. The halothane concentrations of 0.9% and 1.25% were equivalent to 1 MAC of GOF and OF, respectively. The mean arterial pressure (MAP), heart rate (HR), and cardiac index (CI), hepatic arterial blood flow (HABF), portal venous blood flow (PVBF), and total hepatic blood flow (THBF), all decreased dose-dependently after starting inhalation during GOF and OF (1 and 2 MAC). After stopping inhalation, MAP and HABF recovered rapidly, but the recovery of HR was slow and the recovery of CI, PVBF and THBF was poor. GOF of 2 MAC caused remarkable reduction (77.9%) of hepatic oxygen supply. The results indicate that nitrous oxide itself has less effects on hepatic circulation dynamics, and that deep anesthesia of GOF should be avoided since halothane decreases hepatic blood flow dose-dependently.
