Sensory Block Extension During Combined Spinal and Epidural

Background and Objectives During a combined spinal and epidural technique, extension of sensory block by epidural injection of saline or bupivacaine has been demonstrated and attributed to a volume effect or to the combination of a volume effect with a local anesthetic effect. This two-part study was designed to evaluate the time dependency of the volume effect and the local anesthetic effect on the mechanism of spinal block extension. Methods We performed two prospective studies. Thirty patients were randomized in each study. A combined spinal and epidural 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 received 10 mL 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 bupivacaine intrathecally and were placed supine 5 minutes after spinal injection. They then received epidurally either 10 mL saline 7 minutes after spinal (group D) or 10 mL bupivacaine 7 minutes after spinal (group E) or nothing (group F). 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 time from 10 to 40 minutes after spinal injection, and maximum sensory block levels were significantly higher ( P < .05) compared to groups B and C. In the second portion of the study, sensory block levels were comparable at all times in the three groups. Conclusions During a combined spinal and epidural technique with the use of hyperbaric bupivacaine, the volume effect is time 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. The local anesthetic effect is not demonstrated when high sensory block levels are achieved by spinal injection.