Effect of adrenaline on plasma concentrations of fentanyl during epidural anaesthesia for caesarean section

The present study was designed to assess the effect of adrenaline on the plasma concentrations of fentanyl in mothers and umbilical vessels after epidural administration for caesarean section. Thirty patients undergoing elective caesarean section were allocated randomly into two groups. Group 1 (n = 16) received 100 microg fentanyl, 10 ml of 0.5% bupivacaine and 10 ml 2% lidocaine, while group II (n = 14) received 100 microg fentanyl, 10 ml of 0.5% bupivacaine with adrenaline 1:200 000, and 10 ml of 2% lidocaine with adrenaline 1:80 000. Blood samples were obtained from the maternal antecubital vein (MV) at various times up to 6 hours after epidural injection, and from umbilical vein (UV) and arteries (UA) at birth for determination of plasma fentanyl by radioimmunoassay. Fentanyl Cmax and Tmax in MV did not differ significantly between the two groups. In umbilical vessels, plasma fentanyl concentrations were comparable in the two groups: (0.12 +/- 0.08 ng ml(-1) and 0.13 +/- 0.08 ng ml(-1) in UV and 0.08 +/- 0.07 ng ml(-1) and 0.06 +/- 0.05 ng ml(1) in UA of groups I and II respectively). The maximum plasma concentration in UV was 0.24 ng ml(-1) in group I and 0.25 ng ml(-1) in group II. There was no significant correlation between umbilical vessel (vein or artery):MV ratio and dose to delivery interval and no difference between the two groups in Apgar score or umbilical cord pH.