The response of the feline cerebral circulation to PaCO2 during anesthesia with isoflurane and halothane and during sedation with nitrous oxide.

The reduction in cerebral blood flow (CBF) caused by hypocapnia is an important element of neuroanesthetic techniques. While it has been demonstrated previously that the CO2 response of the cerebral circulation (CO2 X R) is enhanced (i.e., greater delta CBF/delta PaCO2) during halothane administration, the effect of isoflurane on CO2 X R has not been evaluated completely. Accordingly, the authors examined CO2 X R in cats during anesthesia with 1.0 MAC isoflurane (with 75% N2O) and compared it with CO2 X R during anesthesia with 1.0 MAC halothane (with 75% N2O) and with CO2 X R during the administration of 75% N2O alone. CO2 X R during anesthesia with isoflurane-N2O was enhanced relative to that observed during administration of both halothane-N2O (P less than 0.025) and N2O alone (P less than .001). CO2 X R during anesthesia with halothane-N2O was, in turn, greater than that observed during the administration of N2O alone (P less than 0.025). Furthermore, at similar levels of hypocapnia (PaCO2 18-20 mmHg), CBF was significantly lower (P less than 0.01) during administration of isoflurane-N2O (29.0 +/- 4.5 ml X 100 g-1 X min-1) than during administration of either N2O (40.6 +/- 5.5 ml X 100 g-1 X min-1) or halothane-N2O (39.6 +/- 7.8 ml X 100 g-1 X min-1). CBF values during administration of the N2O alone and halothane-N2O were not different during hypocapnia.(ABSTRACT TRUNCATED AT 250 WORDS)