Spread of spinal anaesthesia using various doses of plain 0.5% bupivacaine injected at the LIV-V interspace

Spinal anaesthesia with 3 ml, 4 ml or 5 ml of plain 0.5% bupivacaine was performed in three groups of 20 orthopaedic (ASA 1) patients at the LIV-V interspace. Patients aged less than 20 years or more than 60 years and those outside the normal range of body mass index were excluded. The spread of analgesia was greater in the 4-ml and 5-ml groups compared to the 3-ml group at each testing time (P less than 0.05). The mean maximum cephalad spread of pinprick analgesia (+/- s.d.) 60 min after injection was significantly higher (P less than 0.05) in the 4-ml group (T10 +/- 3.2) and in the 5-ml group (T10 +/- 2.7) than in the 3-ml group (T12 +/- 2.1). The interindividual variability of the cephalad spread of analgesia was greater in the 4-ml and 5-ml groups compared to the 3-ml group (P less than 0.05). The degree of motor block was higher in the 5-ml group than in the 3- and 4-ml groups at 5 and 15 min after injection. In seven patients the first sign of motor block was the patient's inability to flex the ankle, rather than inability to raise an extended leg as was the case in the other patients. In all patients satisfactory anaesthesia for surgery of the lower extremity was achieved.