MAC REDUCTION OF ISOFLURANE BY SUFENTANIL

We have shown previously that a plasma fentanyl concentration of 1.67 ng ml(-1) reduced the MAC of isoflurane by 50%. By comparing equal deg rees of MAC reduction by sufentanil, we may determine the potency rati o of these opioids. Seventy-six patients were allocated randomly to re ceive predetermined infusions of sufentanil, and end-tidal concentrati ons of isoflurane in oxygen. Blood samples were obtained 10 min after the start of the infusion, and just before and after skin incision. An y purposeful movement by the patient was recorded. The MAC reduction o f isoflurane produced by sufentanil was obtained using a logistic regr ession model. A sufentanil plasma concentration of 0.145 ng ml(-1) (95 % confidence limits 0.04, 0.26 ng ml(-1)) resulted in a 50% reduction in the MAC of isoflurane. At a plasma concentration greater than 0.5 n g ml(-1), sufentanil exhibited a ceiling effect.