Antihypotensive effect of oxytocin mini-dose at the beginning of spinal anaesthesia for elective caesarean section

Oxytocin is widely used after child delivery for preventing postpartum haemorrhage. Rather high level of spinal block for for Caesarean section has a disadvantage of frequent arterial hypotension. The aim of our study was to assess maternal circulation after mini-dose (0.5 IU) oxytocin administered before, not after, delivery. Methods. Spinal anaesthesia (L3, hyperbaric 0.5% bupivacaine, 13.5 mg) for Caesarean section was performed in 80 women, randomly divided into study (n=40) and control (n=40) groups. In the study group, oxytocin (0.5 IU, slow intravenous bolus) was administered immediately after anaesthesia performance. In both groups, after delivery the slow oxytocin bolus was administered (4.5 IU in study and 5 IU in control group), then another 5 IU were infused in normal saline over 20-25 min. Results. During anaesthesia, minimal systolic arterial pressure (M±SD) in the study group (107±11 Torr) was significantly (p<0.0001) higher than in the control group (88±10 Torr). Phenylephrine administration before delivery was needed in the study group (28 of 40) significantly (Fisher exact p = 0.0015) more rarely than in the control group (39 of 40); whereas during the whole surgery the difference was insignificant (36 of 40 vs 40 of 40, Fisher exact p = 0.1156). Time to first phenylephrine administration in the study group (10.7±4.0 min) was significantly (p<0.0001) longer than in the control group (1.8±1.0 min). Cumulative phenylephrine dose before delivery (Median: min–max) in the study group (1.25: 1,25–2,5 mg) was significantly (p=0.00424) less than in the control group (5: 2.5–6.25 mg). Cumulative phenylephrine dose during the whole surgery in the study group (3.625: 1.25–7.5 mg) was significantly (p<0.00001) less than in the control group (10: 5–12.5 mg). Our results can be explained by blood mobilization from uterine vasculature. Conclusions. Oxytocin mini-dose (0.5 u), administered at the beginning of spinal anaesthesia for Caesarean section, attenuates arterial hypotension and allows less phenylephrine use.