Cerebral responses to the addition of nitrous oxide to halothane in man

Cerebral responses to the substitution of 60% nitrous oxide for 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 oxygen tension during halothane anaesthesia, 17+/-3 ml blood/ml oxygen and 41+/-2 mm Hg respectively, increased significantly to 45+/-3 ml blood/ml oxygen and 54+/-3 mm Hg following the introduction of nitrous oxide. On the withdrawal of nitrous oxide, the mean cerebral blood flow equivalent and internal jugular venous oxygen tension returned gradually to the control values. Cerebral perfusion pressure and blood-gas values, other than the internal jugular venous oxygen tension, did not change significantly. Marked slowing of the e.e.g. was observed following the addition of nitrous oxide to halothane, Upon the withdrawal of nitrous oxide the e.e.g. returned to the control pattern. These results indicate that cerebral blood flow was in excess of oxygen demand during nitrous oxide/halothane anesthesia in man.