Purpose: To determine, after Caesarean delivery, uterine contractility and blood pressure following intravenous (i.v.) and intramyometrial (imy) injection of oxytocin.
Methods: In a double-blind clinical trial 40 parturients scheduled for elective Caesarean section with spinal anaesthesia were randomized into two equal groups. One litre Ringer's lactate was administered i.v. before intrathecal injection of 1.7 ml bupivacaine 0.75% and 0.3 mg morphine. All patients received simultaneous i.v. and imy injections after removal of the placenta. Patients in Group 1 received 5 IU (10 IU.ml-1) oxytocin i.v. and 2 ml saline imy: Group 2 patients received 0.5 ml saline i.v. and 20 IU oxytocin into the myometrium. Baseline systolic blood pressure (SBP) and heart rate were measured before delivery and at one minute intervals for 15 min after injection of study solutions. Uterine contractility was assessed at 1, 2, 4, 6, 8, 10 and 15 min after oxytocin injection. Haemoglobin concentration before surgery and on first post-operative day was also recorded.
Results: Mean decrease in systolic blood pressure (SBP) one minute after oxytocin was 8.4 mmHg in Group vs 14.6 mmHg in Group 2 (P < 0.001). Systolic blood pressure returned to baseline two minutes after oxytocin in Group 1 and after three minutes in Group 2. Uterine contractility and change in haemoglobin concentration were similar in both groups.
Conclusion: Intramyometrial administration of 20 IU oxytocin after Caesarean delivery is associated with more severe hypotension than is i.v. injection of 5 IU oxytocin. Route of oxytocin injection did not affect uterine tone.