Duration of Spinal Anesthesia with Bupivacaine in Chronic OpiumAbusers Undergoing Lower Extremity Orthopedic Surgery

It has been demonstrated that chronic opium abusers have lower thresholds for pain. Spinal anesthesia is a common procedure in anesthesia, which is performed through administration of drugs (usually local anesthetics) in the intrathecal space, to produce temporary pain relief. The aim of this study was to determine whether chronic opium abuse could have any possible effect on the duration of spinal block by bupivacaine. In a case-control study, 50 opium abusers and 50 nonabusers undergoing lower extremity orthopedic operations were selected from the patients admitted in Taleghani Hospital in Tehran for elective surgery. The study parameters were assimilated as much as possible, including the method of anesthesia. No statistically significant difference was noted between the two groups regarding the age, sex, and duration of surgery; while, the duration of sensory block was much shorter in the opium abusers (86.6 ± 15.7 minutes) compared with the nonabusers (162 ± 22.1 minutes) (P < 0.0001). The study suggests a shortened duration of spinal block with bupivacaine in opium abusers. The results can propose a number of possible mechanisms including cross-tolerance mechanisms between local anesthetics and opioid compounds at the level of spinal neurons. Further molecular studies at the level of spine are suggested.