Effect of sitting position on equal-dose spinal anaesthetic for caesarean section and post-partum tubal ligation

Background We studied the hypothesis that an equal spinal anaesthetic dose administered in the sitting position to patients undergoing post-partum tubal ligation (PPTL) and caesarean section (CS) would yield similar sensory block characteristics and analgesic efficacy. Methods This prospective, non-randomised trial recruited 20 women undergoing PPTL within 48h of vaginal delivery and 20 undergoing CS. Spinal anaesthesia comprising intrathecal hyperbaric bupivacaine 12mg and morphine 100g was administered at L3/4 with patients sitting. Our primary end point was the maximal dermatomal sensory block (to cold). Results Baseline demographics were comparable, but PPTL patients had greater parity, with mean +/- standard deviation 17.54 +/- 11.2h from delivery to spinal anaesthesia, and shorter duration of surgery, 17.54 +/- 11.2 vs. 40.3 +/- 15.5min. Similar maximal sensory blocks (to cold) were achieved in group PPTL vs. CS, T4 (T1-T5) vs. T3 (T1-T5), P=0.104, in comparable times, 8.6 +/- 2.6 vs. 7.6 +/- 3.0min, P=0.267. PPTL patients had significantly faster two-segment block regression (70.7 +/- 23.5 vs. 97.6 +/- 23.9min, P=0.001) and to T10 (120.8 +/- 35.6 vs. 145.1 +/- 24.3min, P=0.016), with less hypotension (25% vs. 65%, P=0.025) and phenylephrine (20.0 +/- 60.6g vs. 120.0 +/- 119.6g, P=0.005). Conclusion The same dose of hyperbaric bupivacaine 12mg and morphine 100g administered in the sitting position to both PPTL and CS parturients yielded similar maximal sensory blocks, but PPTL exhibited faster block regression and less hypotension/vasopressor requirement.