Knee-chest vs horizontal side position during induction of spinal anaesthesia in patients undergoing lumbar disc surgery

In the prone knee-chest position the spread of plain 0.5% bupivacaine inthe cerebrospinal fluid and associated haemodynamic changes may bedifferent compared with the horizontal position. A randomized comparisonwas performed in 40 ASA I-II patients, aged 24-61 yr, undergoing lumbardisc surgery. Subarachnoid injection (27-gauge needle) at the L2-3interspace with 3 ml of 0.5% bupivacaine was performed with the patient inthe operative knee-chest position (prone knee-chest group, n = 20) or inthe horizontal side position (supine side horizontal group, n = 20).Patients in the supine side horizontal group were turned into thehorizontal supine position for 20 min, and subsequently they were placed inthe operative knee-chest position. In three patients in the proneknee-chest group, the spinal needle was replaced by a larger needle(25-gauge). The final cephalad extension of sensory analgesia on skintested by pinprick was T5 (median) in the prone knee-chest group and T6 inthe supine side horizontal group. Recovery was also similar, on average 210min from injection in both groups. The mean decrease in systolic arterialpressure was somewhat greater in the prone knee-chest group (30 mm Hg) thanin the supine side horizontal group (13 mm Hg). The need for ephedrineoccurred earlier in the supine side horizontal group (three patients, allwithin 10 min from local anaesthetic injection) than in the proneknee-chest group (six patients, all after 15 min). Four of the latterpatients also required administration of an anticholinergic for bradycardiacompared with two patients in the supine side horizontal group. Lightsedation was given to five patients in the prone knee-chest group and tofour in the supine side horizontal group because of numbness and aching inthe shoulders. We conclude that spinal block was similar in the two groupsbut there was a tendency to more frequent episodes of haemodynamicdeterioration in the knee-chest position.