REDUCTION OF BLOOD-LOSS DURING SPINAL SURGERY BY EPIDURAL BLOCKADE UNDER NORMOTENSIVE GENERAL-ANESTHESIA

Study Design. This study consisted of a comparison of intraoperative b lood loss during posterior spine surgery under normotensive general an esthesia with and without epidural blockade, and a hemodynamic study a fter epidural injection.Objectives. To determine the effect of epidura l blockade in reducing blood loss and intraosseous pressure in the ver tebral body. Summary of Background Data. Epidural anesthesia is effect ive in reducing surgical bleeding. This effect has been thought to be due to systemic arterial hypotension. There was no report on its effec t on venous pressure or intraosseous pressure. Methods. In comparison of blood loss, epidural blockade was achieved by preincisional caudal epidural injection of 20 ml of 0.25% bupivacaine during cervical lamin oplasty or posterior lumbar interbody fusion. For each surgical proced ure, there were 20 patients who recieved epidural blockade and 20 who did not. In a hemodynamic study, intraosseous pressure in the second t horacic or the second or third lumbar vertebral body, intraosseous pre ssure in the calcaneus, and systemic arterial blood pressure were meas ured continuously before and after the caudal epidural injection of 20 ml of 1% lidocaine during posterior cervical or lumbar spine surgery in 42 patients. Results. Total and hourly intraoperative blood loss du ring posterior lumbar interbody fusion was significantly less in the g roup with blockade than in the group without blockade, but the values during cervical laminoplasty showed no significant difference between the two groups. The lumbar vertebral intraosseous pressure decreased s ignificantly after epidural injection, whereas the second thoracic ver tebral and the calcaneal intraosseous pressure did not decrease signif icantly. The ratio of lumbar vertebral intraosseous pressure to arteri al pressure decreased continuously after epidural injection, whereas t he ratio of the calcaneal intraosseous pressure to arterial pressure t ransiently increased. Conclusions. The epidural blockade reduces intra operative bleeding, even under normotensive conditions, and it takes e ffect in the lumbar spine, but not in the upper thoracic or cervical s pine. This effect appears to be due chiefly to venous hypotension in t he lumbar spine, which may be created by sympathetic blockade, with ar teriolar dilatation and venous pooling in the lower limbs and reactive vasoconstriction in the lumbar vertebrae.