Onset of spinal block is more rapid with isobaric than hyperbaric bupivacaine

Purpose: To compare isobaric with hyperbaric 9.75 mg bupivacaine injected i ntrathecally, and to evaluate the effects of subsequent injection of lidoca ine 2% into the epidural space. Methods: Patients in group I (n = 30) received isobaric 9.75 mg bupivacaine and in group 2 (n = 30) hyperbaric 9.75 mg bupivacaine injected into the s ubarachnoid space in a combined spinal-epidural technique, They were underg oing urological, gynecological, orthopedic, gastro-intestinal or vascular s urgery. Using a double blind technique, the followings parameters were meas ured: cutaneous analgesia to pinprick, motor blockade, time for two segment regression, time for complete regression of the motor block, quality of an esthesia. In 12 patients the effect of epidural injections of 3 ml lidocain e 2% was observed. Results: Motor and sensory block developed more rapidly (five minutes) in t he isobaric group (P < 0.05). Maximum upper level (T7 +/- 2), two-segment r egression (52 min in both groups), motor recovery (160 vs 157 min), and qua lity of anesthesia did not differ between the two groups. Thirty nine epidu ral injections of 3 mi lidocaine 2% were given in 12 patients 10 min after spinal injection, 28 were in the hyperbaric group (P < 0.05). Twenty six of the epidural injections produced an increase in sensory block of 0 or 1 de rmatome, and 13, of 2 or more. Conclusion: The block developed more rapidly in the isobaric group, but bot h isobaric and hyperbaric 9.75 mg bupivacaine produced adequate upper level s of analgesia for surgery. The effect of epidural injections of 3 mi lidoc aine 2% was usually minimal.