SENSORY BLOCK EXTENSION DURING COMBINED SPINAL AND EPIDURAL

Background and Objectives. During a combined spinal and epidural techn ique, extension of sensory block by epidural injection of saline or bu pivacaine has been demonstrated and attributed to a volume effect or t o the combination of a volume effect with a local anesthetic effect. T his two-part study was designed to evaluate the time dependency of the volume effect and the local anesthetic effect on the mechanism of spi nal block extension. Methods. We performed two prospective studies. Th irty patients were randomized in each study. A combined spinal and epi dural was performed in a sitting position in all groups. The patients in the first study received 15 mg hyperbaric bupivacaine intrathecally and were placed supine 2 minutes after spinal injection. They receive d 10 mt epidural saline either 5 minutes after spinal (group A) or 20 minutes after spinal (group B) compared to a control group (group C). The patients in the second study received 12.5 mg hyperbaric bupivacai ne intrathecally and were placed supine 5 minutes after spinal injecti on. They then received epidurally either 10 mL saline 7 minutes after spinal (group D) or 10 mt bupivacaine 7 minutes after spinal (group E) or nothing (group Fl, Sensory block levels were assessed by a loss of sensation to cold using ether. Results. In the first portion of this study, in group A, area under the curve of sensory block levels by tim e from 10 to 40 minutes after spinal injection, and maximum sensory bl ock levels were significantly higher (P <.05) compared to groups B and C. In the second portion of the study, sensory block levels were comp arable at all times in the three groups. Conclusions. During a combine d spinal and epidural technique with the use of hyperbaric bupivacaine , the volume effect is lime dependent and is seen when epidural top up is done soon after spinal injection. This volume effect is abolished when patients are left seated for 5 minutes after spinal injection. Th e local anesthetic effect is not demonstrated when high sensory block levels are achieved by spinal injection.