Influence of obesity on the spread of spinal analgesia after injection of plain 0.5% bupivacaine at the l3-4 or l4-5 interspace

Abstract

Summary: Spinal anaesthesia was compared in 40 obese patients (increased body mass index (BMI)) and 40 patients with normal BMI when 3 ml of plain 0.5% bupivacaine was injected at either the L3-4 or L4-5 interspace. More extensive cephalad spread of sensory block was achieved in patients with increased BMI compared with patients with normal BMI after injection at both L3-4 and L4-5 (P < 0.05). The use of the L3-4 interspace instead of L4-5 resulted in a higher mean spread of block in patients with both increased (T4 vs T8) or normal (T9 vs T11) BMI (P < 0.05). The interindividual variability of the blocks was relatively small in patients with normal BMI injected at L4-5, compared with the three other groups (normal BMI injected at L3-4, increased BMI injected at L3-4 and L4-5). Good anaesthesia was produced in all patients for orthopaedic surgery of the lower extremity. In an obese patient it is recommended that plain bupivacaine be administered at L4-5 instead of L3-4 when extensive spread of the block is to be avoided. © 1990 Copyright: 1990 British Journal of Anaesthesia.