THE EFFECT OF INCREASING THE DOSE AND VOLUME OF EPIDURAL INJECTATE IN COMBINED SPINAL EPIDURAL ANAESTHESIA

BACKGROUND: Augmentation of the level of spinal sensory block after an epidural injection in combined spinal epidural anesthesia may be explained by a dual mechanism: a volume effect due to the compression of the thecal sac and a local anesthetic effect. AIMS: The purpose of our study was to investigate the effect of increasing the dose and volume of epidural injectate in combined spinal epidural technique. SETTINGS AND DESIGN: Prospective randomized controlled and double blind. METHODS AND MATERIAL: Fifty adult patients scheduled for lower limb surgery under combined spinal epidural anesthesia were randomly allocated to one of the five groups comprising 10 patients each. All patients received a combined spinal epidural injection using a needle through needle technique. An intrathecal injection of 10 mg (2ml) of 0.5% hyperbaric bupivacaine was given and an epidural catheter inserted in all the cases. After the maximal level of sensory blockade was attained, an epidural injection was administered according to the designated randomization code. Group I received nothing and served as the control. Groups II, III, IV & V received 20 ml of 0.25% Bupivacaine, 20ml of saline, 10ml of 0.25% Bupivacaine & 10ml of saline respectively through the epidural catheter. STATISTICAL ANALYSIS: The observations were analyzed using Chi square and paired t test. RESULTS: Significant rise in the level of sensory analgesia was observed in groups II to V following the epidural injection while no change was observed in the control group. Maximum rise was observed in Group II where the dose as well as volume was maximum. CONCLUSION: We conclude that increasing the dose and volume of injectate increases the effective sensory block when utilizing the epidural volume extension technique; even after maximal sensory blockade of spinal has been achieved.