A Comparative Study of Block Characteristics and Side Effects of Intrathecal versus Intravenous Fentanyl for Supplementation of Subarachnoid Block in Patients Undergoing Total Abdominal Hysterectomy

Introduction: Although there are studies comparing various opioids and various dosages of fentanyl, studies comparing the two routes of administration, especially for total abdominal hysterectomy are very few. Methods: Inj. fentanyl 25µg (0.25ml) intrathecally and Inj. fentanyl 1µg/kg intravenously were compared.15 mg of 0.5% hyperbaric bupivacaine was used for spinal anaesthesia in both groups. Onset of sensory blockade, maximum level of sensory blockade attained, and the time taken for the same were noted. Time taken for onset of motor blockade, i.e., Bromage 6, and time taken to achieve maximum motor block, i.e., Bromage 1, were noted. Time for two-segment sensory regression, time for sensory regression to T12, time for motor regression to Bromage 6, and the level of sedation by using the Ramsay sedation score were also recorded. Time for rescue analgesia using 75 mg diclofenac intramuscularly when patient complained of mild pain or VAS > 5 was also noted. Results: The mean onset of sensory blockade in minutes was 1.94±0.85 in IT fentanyl and 1.59±0.71 in IV fentanyl, p <0.008. The mean onset of motor blockade in minutes was 3.16±1.06 in IT fentanyl and 2.71±0.84 in IV fentanyl, p <0.007. The mean time for maximum sensory blockade in minutes was 17.50±4.76 in IT fentanyl and 19.44±4.43 in IV fentanyl, p <0.014. The mean time for maximum motor blockade in minutes was 5.44±1.53 in IT fentanyl and 4.91±1.02 in IV fentanyl, p <0.017. The mean regression of sensory blockade to T12 in minutes was 192.84±32.80 in IT fentanyl and 176.23±19.81 in IV fentanyl, p <0.001. The mean regression of motor blockade to T12 in minutes was 163.76±37.40 in IT fentanyl and 152.16±22.39 in IV fentanyl, p <0.028. The time to rescue analgesia in minutes was 216.81±38.79 in IT fentanyl and 184.43±16.91 in IV fentanyl, p <0.001. About 87% of patients had an RSS score of 2, and 13% had an RSS score of 3 in IT fentanyl. 74% of patients had an RSS score of 2, and 26% had an RSS score of 3 in IV fentanyl. About 4% of patients had nausea and vomiting and about 13% had hypotension in the IT fentanyl group, whereas the IV fentanyl group had about 14% of patients with nausea and vomiting, 16% with hypotension, and 4% with pruritus. Conclusion: Intrathecal fentanyl 25µg compared to intravenous fentanyl 1µg/kg administered with 0.5% hyperbaric bupivacaine for subarachnoid block in total abdominal hysterectomies, prolonged sensory and motor block, increased the duration of analgesia with fewer adverse effects.