Effect of intrathecal fentanyl on oxytocin secretion in pregnant women not in labour

We studied the effects of spinal intrathecal fentanyl on oxytocin secretion in 20healthy women prior to an elective caesarean delivery at term under spinal anaesthesia. The women were randomly allocated into two groups with respect to spinal anaesthesia. Group I (n = 10) received intrathecal bupivacaine (15mg) plus fentanyl (25μg), and Group II (n = 10) received intrathecal bupivacaine (15mg) alone, prior to caesarean section. The two groups were comparable demographically. Altogether, ten samples of 4.5ml of blood (taken every 60 s) were obtained before and ten samples were obtained after the intrathecal administration of the drug and establishment of the T6 block, and plasma oxytocin concentrations were assayed for each subject. Oxytocin was measured by RIA. We found no significant differences in plasma oxytocin concentrations of individual subjects before and after intrathecal injection. In addition, there were no significant differences in plasma oxytocin concentrations between the two groups when pooled samples from the subjects were compared for the pre- and post-intrathecal injection phases. We conclude that the spinal intrathecal administration of fentanyl does not suppress oxytocin secretion in pregnant women who are not in labour at term.