Can density influence the spread of intrathecal bupivacaine in the prolonged sitting position before elective caesarean section?

Abstract

Introduction: Disadvantages of the combined spinal epidural (CSE) technique include prolonged delays in siting the epidural catheter, which may result in inadequate spinal anaesthetic spread. This randomised, double-blind study was designed to test the theory that spinal solutions of varying density would behave differently under such conditions. Method: Following ethics approval, 90 women undergoing elective caesarean section under CSE were randomised into three groups (n = 30 per group) receiving either hyperbaric, isobaric or hypobaric (densities determined from a previous study 1) bupivacaine 10 mg with fentanyl 15/zg intrathecally, in the sitting position. Any posture-related effects on density between the solutions were potentially exaggerated by keeping patients sitting for 5 min before lying in a supine wedged position. Data collection included sensory level (cold, pinprick, touch) and motor block assessment while sitting, immediately on lying down and at further 5-min intervals for 20 rain as well as hypotensive episodes, ephedrine use, and neonatal data. Statistical analysis included ANOVA, Kruskal Wallis and Cuzick's trend test (P < 0.05). Results: Although sensory levels did not significantly differ between groups during 5 min of sitting (P = 0.53), all solutions demonstrated increased cephalad spread immediately on lying supine (figure), with significant trends of increasing block height, hypotension and ephedrine use with decreasing spinal solution density (P < 0.0001) over the 20-rain study period.