PHENYLEPHRINE DOSES FOR THE PREVENTION OF OXYTOCIN-INDUCED HYPOTENSION IN CAESAREAN SECTION: EFFECT OF PRELOAD

Abstract

INTRODUCTION: Approximately 80% of the patients suffers Spinal-induced hypotension (SIH) for cesarean delivery (CD) and is a frequently encountered problem. Phenylephrine is a short-acting alpha agonist, can be administered by bolus as well as by infusion to treat oxytocin induced hypotension. Phenylephrine has been associated with a decreased incidence of hypotension and maternal nausea and vomiting and improved umbilical artery pH.

MATERIAL AND METHODS: Via computer-generated blocked randomization patients were randomized to be in the colloid or crystalloid infusion groups. 18-gauge intravenous (IV) catheter was inserted into a forearm vein, and vein patency was maintained with Lactated Ringer's solution (LR) at a rate of 5 ml/h before administering the preload. Colloid preload was 500 ml hydroxyethyl starch in 0.9% normal saline and crystalloid preload was LR (1500 ml). Volume of crystalloid and colloid preload was 1:3 colloid to crystalloid ratio to achieve a similar degree of volume expansion. Spinal anaesthesia was given with a 25-gauge pencil point needle at the L2-L3 or L3-L4 vertebral interspace. A mixture of hyperbaric bupivacaine 0.75%, 12 mg with morphine, 200 mcg was injected intrathecally. All patients were given a phenylephrine infusion (10 mg phenylephrine in 100 ml 0.9% NS). Just after intrathecal injection at a rate of 100 mcg/min. Phenylephrine infusion protocol was continued until the time of uterine incision. The infusion was stopped if the HR decreased below 60 beats per minute (bpm), or if the SBP increased to >20% above baseline, and was again restarted when the BP decreased to <20% below baseline (defined as hypotension). The total dose of phenylephrine used during the study period was recorded.

RESULTS: A total of 92 patients were included in the study, 56 in each group. 2 patients from crystalloid preload group were excluded because of the high sensory levels and 2 patients from colloid group was excluded because of significant hypertension prior to starting the phenylephrine infusion. Finally 54 patients in each group were included in the study. Mean age in lacteted ringer solution group was 27.21±6.24 years while in hydroxyethyl starch group it was 28.14±5.49. Mean Spinal uterine incision time was 16.58±4.21 and 18.28±3.39 in lacteted ringer solution group and hydroxyethyl starch group respectively. Estimated blood loss in ml(mean±SD) was 446±60.89 and 498±59.45 in lacteted ringer solution group and hydroxyethyl starch group respectively. Systolic blood pressure baseline (mean±SD) 128.88±10.28 and 131.31±9.54 in lacteted ringer solution group and hydroxyethyl starch group respectively. Heart rate (mean±SD) was 90.87±10.25 and 88.56±11.56 in lacteted ringer solution group and hydroxyethyl starch group respectively. Significantly less phenylephrine was used in the colloid group (1068 ± 554 mcg) compared to the crystalloid group (1401 ± 527 mcg) (P = 0.003) . There was no significant difference in the incidence of maternal nausea and vomiting, as well as APGAR scores at 1 and 5 min. Emergency rescue medications were administered to a total of 4 patients. 3 in crystalloid group and 1 in colloid group for supraventricular tachycardia.

CONCLUSION: In prevention of SIH and treatment Phenylephrine with colloids are shown to be superior to crystalloids because of the phenylephrine sparing effect.