CEREBRAL RESPONSES TO THE ADDITION OF NITROUS OXIDE TO HALOTHANE IN MAN

Cerebral responses to the substitution of 60% nitrous oxidefor nitrogen during halothane anaesthesia (0.84%, end-tidal)were studied in four patients during surgery. The mean (±SEM)cerebral blood flow equivalent and internal jugular venous oxygentension during halothane anaesthesia, 27±3 ml blood/mloxygen and 41±2 mm Hg respectively, increased significantlyto 45±3ml blood/ml oxygen and 54±3 mm Hg followingthe introduction of nitrous oxide. On the withdrawal of nitrousoxide, the mean cerebral blood flow equivalent and internaljugular venous oxygen tension returned gradually to the controlvalues. Cerebral perfusion pressure and blood-gas values, otherthan the internal jugular venous oxygen tension, did not changesignificantly. Marked slowing of the e.e.g. was observed followingthe addition of nitrous oxide to halothane. Upon the withdrawalof nitrous oxide the e.e.g. returned to the control pattern.These results indicate that cerebral blood flow was in excessof oxygen demand during nitrous oxide/halothane anaesthesiain man. This work was performed at the Department of Anaesthesiology,Yamaguchi University Hospital.