Effect of late posture change on the level of spinal anaesthesia with plain bupivacaine

We studied 40 patients, 18-60 yr, undergoing orthopaedic surgery of the lower limb under spinal anaesthesia. A midline lumbar puncture was performed in the L3-4 interspace using a 27-gauge needle with the patient in the lateral horizontal position. Plain bupivacaine 3 ml at room temperature was injected. The cephalad level of analgesia was assessed by pinprick 60 min after injection of local anaesthetic, at the end of surgery and again after the patient was moved into bed. All patients had a segmental level of the block of L1-T5 at the beginning of the study. The upper half of the patient's body was then tilted to a 30 degrees head-up position. Segmental spread was subsequently assessed by pinprick at 5-min intervals for 30 min. In six of the 40 patients (15%), increased cephalad spread of spinal analgesia occurred. The mean time from induction of spinal anaesthesia was shorter in these six patients (mean 92 min, range 80-115 min) than in the patients whose block did not change or was decreasing during the 30-min test (mean 119 min, range 83-210 min) (P < 0.05). We conclude that the patient should remain in the supine horizontal position until recovery from the spinal block.