comparison of the sensory-motor block effects of low dose hyperbaric bupivacaine and lidocaine in anorectal surgery with spinal anesthesia

background & objective: outpatient surgery can be performed by general or spinal anesthesia. spinal anesthetic drugs have side effects. many anesthesiologists choose general anesthesia, because of its relative predictability and to avoid undesirable side effects associated with spinal anesthesia. for example lidocaine is frequently associated with transient neuroligic symptoms (tns). bupivacaine may cause urinary retention, prolonged discharge time and unpredictable level of anesthesia dependent on dose. reducing bupivacaine dose will shorten the duration of action and its anesthesia level will be predictable in saddle block technique. this study was designed to assess the effects of hyperbaric, low dose bupivacaine in level of sensory block, duration of anesthesia and selective sensory block in an rectal surgery and its comparison with lidocaine. materials & methods: in a clinical trial study, 64 patients who were the candidates for anorectal surgery were divided in two groups randomly. in one group, hyperbaric bupivacaine 0.5% was injected in sitting position. the other group received hyperbaric lidocaine 5% in the same position. the patients were laid in lithotomy position after 5 minute. blood pressure, pulse rate, severity of sensory & motor block, duration of anesthesia and tonicity of anal sphincter were recorded in two groups. the results were analyzed through t-test, chi square and variance analysis. results: sensory level and anesthesia duration in bupivacaine group were higher than lidocaine group. motor block degree and anal sphincter tonicity loss in lidocaine group were greater than the other one. blood pressure decreasing in lidocaine group was significantly higher to bupivacaine group. conclusion: the proper sensory level and short anesthetic duration of low-dose hyperbaric bupivacaine are comparable with lidocaine in saddle block position, and selective sensory block may be useful for anorectal surgery in lithotomy position.