Combined spinal-extradural anaesthesia for preterm and term caesarean section: is there a difference in local anaesthetic requirements?

Abstract

In a non-blinded observational study, we have tested the null hypothesis that there is no difference in local anaesthetic requirements for subarachnoid anaesthesia between women presenting for Caesarean section at term or preterm (38-42 and 28-35 weeks' gestation, respectively). Using a combined spinal-extradural technique, 2.25 ml of 0.5% hyperbaric bupivacaine was given, in the sitting position, to 50 women presenting for Caesarean section. In 21 of 25 preterm women, adequate sensory block for surgery did not develop (P < 0.001) and they required supplementary extradural local anaesthetic (median 8 ml of 2% lignocaine with 1:200,000 adrenaline (interquartile range 4-12 ml)); preterm women not requiring extradural supplementation were at the upper end of the gestational range. There was a strong linear correlation between increasing gestation and block height in the preterm group (Spearman rank correlation coefficient = 0.74; 95% confidence intervals 0.49, 0.88). All women in the term group developed adequate anaesthesia with the subarachnoid dose alone. Onset of anaesthesia was slower in the preterm group (median 15 vs 5 min) with a lower incidence of hypotension (P = 0.0005).