A Comparison of Subarachnoid Block Characteristics Following Co-administration of Fentanyl Premixed With Hyperbaric Bupivacaine Versus Antecedent or Succedent to Hyperbaric Bupivacaine: A Randomized Controlled Study.

Background Adjuvants are often used during subarachnoid block to enhance and prolong the analgesia and decrease the adverse effects of high doses of local anesthetic agents. Intrathecal fentanyl premixed with hyperbaric bupivacaine has been used in spinal anesthesia and compared with the sequential use of these drugs in separate syringes. However, given the paucity of literature, we conducted this study where premixed antecedent and succedent administration of intrathecal fentanyl with hyperbaric bupivacaine were compared in terms of flow dynamics, block characteristics, and hemodynamic alterations. Methodology This prospective, randomized, triple-blinded comparative study was conducted among 160 patients who were randomly allocated into four groups. Group A (n = 40) (control) received 3.0 mL (15 mg) of 0.5% hyperbaric bupivacaine and 0.5 mL of normal saline via a 5.0 mL syringe. Group B (n = 40) received 3.0 mL (15 mg) of 0.5% hyperbaric bupivacaine and 0.5 mL (25 µg) of fentanyl premixed via a single 5.0 mL syringe. Group C (n = 40) received 0.5 mL (25 µg) of fentanyl via a 1.0 mL syringe followed by 3.0 mL (15 mg) of 0.5% hyperbaric bupivacaine via a 5.0 mL syringe. Group D (n = 40) received 3.0 mL (15 mg) of 0.5% hyperbaric bupivacaine via a 5.0 mL syringe followed by 0.5 mL (25 µg) of fentanyl via a 1.0 mL syringe. The onset and regression of sensory and motor blockade, hemodynamic parameters, time to first rescue analgesia, and adverse events were observed. Data analysis was done using SPSS version 17.0 (SPSS Statistics Inc., Chicago, IL, USA). Results The mean time taken for the onset of sensory and motor blockade was least in Group D followed by Group C. Duration of sensory and motor blockade was prolonged in Group D. Patients in Group A experienced more hypotension than Groups B, C, and D. Requirement of rescue analgesia was delayed in Groups C and D. Conclusions Administering 25 µg (0.5 mL) of Fentanyl separately after 15 mg (3.0 mL) of 0.5% hyperbaric bupivacaine results in early onset and prolonged duration of sensory and motor blockade, intraoperative hemodynamic stability, the delayed requirement of rescue analgesia postoperatively, and fewer side effects compared to its co-administration as a premixed solution or antecedent to hyperbaric bupivacaine.