Postoperative pain following lower abdominal surgery is a major concern, as inadequate pain control can delay recovery, increase morbidity, and prolong hospital stay. Spinal anaesthesia using 0.5% hyperbaric bupivacaine is a popular and effective technique for such procedures, offering reliable surgical anaesthesia with rapid onset. However, its duration of postoperative analgesia is limited, leading to early analgesic requirement. To overcome this limitation, intrathecal adjuvants particularly opioids are increasingly used to prolong pain relief while minimizing systemic adverse effects. Among available adjuvants, nalbuphine and buprenorphine are of special interest due to their unique pharmacological profiles and safety at low intrathecal doses. Nalbuphine is a mixed opioid agonist–antagonist that primarily stimulates κ-receptors and antagonizes μ-receptors, providing good analgesia while reducing typical μ-mediated side effects such as respiratory depression, pruritus, and nausea [1]. Several studies have demonstrated that intrathecal nalbuphine effectively prolongs the duration of sensory block and postoperative analgesia when combined with bupivacaine for abdominal and gynaecological procedures, with minimal adverse reactions [2]. Buprenorphine, on the other hand, is a highly lipophilic partial μ-agonist and κ-antagonist with strong receptor affinity and slow dissociation, resulting in dense, prolonged segmental analgesia. It provides effective postoperative pain relief with a ceiling effect on respiratory depression [3]. Clinical studies using intrathecal buprenorphine (60–150 µg) in combination with bupivacaine have shown significantly prolonged time to first rescue analgesic and improved block characteristics, with acceptable incidences of nausea and pruritus [4]. Although both agents have proven individually effective, direct comparative studies are limited. A double-blind study in orthopaedic surgery demonstrated that buprenorphine produced longer analgesia than nalbuphine, with similar hemodynamic stability and side-effect profiles [5]. However, variations in nalbuphine dose (0.6–1.6 mg), buprenorphine dose (60–150 µg), surgical settings, and outcome measures in existing literature limit the generalizability of findings to lower abdominal surgeries [6]. Pharmacologically, nalbuphine’s κ-agonism may reduce μ-mediated side effects such as pruritus and nausea, while buprenorphine’s high μ-affinity and lipophilicity account for its longer analgesic duration but slightly higher incidence of nausea in some cases [7]. Despite several studies demonstrating the benefits of intrathecal nalbuphine and buprenorphine separately, there is a paucity of adequately powered, head-to-head trials in adult lower abdominal surgeries using standardized doses and uniform outcome measures. Most available studies are small, single-centre, and involve non-comparable dosing schedules, making it difficult to determine which drug provides the optimal balance between prolonged analgesia and minimal adverse effects [8]. The present study aimed to compare the efficacy and safety of intrathecal nalbuphine (0.8 mg) and buprenorphine (60 µg) as adjuvants to 0.5% hyperbaric bupivacaine in adult patients undergoing lower abdominal surgeries under spinal anaesthesia. The objectives were to evaluate the onset and duration of sensory and motor block, time to first rescue analgesic, 24-hour analgesic requirement, postoperative pain scores, hemodynamic parameters, and side effects such as nausea, vomiting, pruritus, respiratory depression, and urinary retention.

Study Design and Setting This prospective, randomized comparative study was conducted in the Department of Anaesthesiology, Khajah Banda Nawaz Teaching and General Hospital, Kalaburgi, from December 2018 to June 2020. Ethical clearance was obtained, and written informed consent was taken from all participants. Study Population and Groups A total of 100 ASA I–II patients, aged 18–45 years, scheduled for elective lower abdominal surgeries under spinal anaesthesia, were randomly divided into two equal groups (n=50 each): • Group N: 3 ml of 0.5% hyperbaric bupivacaine + 0.2 ml (0.8 mg) nalbuphine intrathecally. • Group B: 3 ml of 0.5% hyperbaric bupivacaine + 0.2 ml (60 µg) buprenorphine intrathecally. Inclusion and Exclusion Criteria Inclusion: ASA I–II patients, aged 18–45 years, consenting for elective lower abdominal surgeries lasting 90–120 minutes. Exclusion: Pregnancy/lactation, failed spinal block, allergy to study drugs, chronic pain, need for general anaesthesia supplementation, or ongoing analgesic therapy. Preoperative Evaluation All patients underwent detailed pre-anaesthetic assessment including history, physical and systemic examination, airway (Mallampati) grading, and spine evaluation. Routine investigations (CBC, LFT, RFT, coagulation profile, HIV, HBsAg, ECG, chest X-ray, urine analysis) were performed. Anaesthetic Technique Patients were kept NPO for 6 hours, preloaded with Ringer’s lactate (10 ml/kg), and monitored for HR, NIBP, ECG, and SpO₂. Under aseptic precautions, spinal anaesthesia was administered at L3–L4 using a 25G Quincke needle. After confirming free CSF flow, the study drug was injected intrathecally. Patients were placed supine; onset of sensory block (by pinprick) and motor block (Bromage scale) was noted. Surgery commenced after achieving T6 sensory and Grade 3 motor block. Hemodynamic parameters were recorded at baseline, 0, 1, 3, 5, 10 minutes, and every 15 minutes until surgery completion. Parameters Observed • Hemodynamics: HR, SBP, DBP, SpO₂. • Sensory/Motor Block: Onset, time to maximum block, and two-segment regression. • Analgesia: Duration (injection to first rescue, VAS >3). • Pain Assessment: VAS every 30 min for 2 h, then hourly for 12 h. • Adverse Effects: Nausea, vomiting, hypotension, bradycardia, pruritus, or respiratory depression. Rescue and Management • Bradycardia: Atropine 0.6 mg IV. • Hypotension: Mephentermine 6 mg IV. • Respiratory depression: Supplemental O₂ via facemask. • PONV: Metoclopramide 10 mg IV. • Rescue analgesia: Diclofenac 75 mg IM when VAS >3. Statistical Analysis Data were analyzed using SPSS 18.0, SAS 9.2, Stata 10.1, and R ver.2.11.1. Continuous variables were compared with the unpaired t-test, categorical variables with the Chi-square test, and normality with the Kolmogorov–Smirnov test. Results with p < 0.05 were considered statistically significant.

Table 1: Age-wise Distribution of Patients Age (years) Group N (n=50) % Group B (n=50) % Total (n=100) % ≤ 20 8 16.0 7 14.0 15 15.0 21–30 17 34.0 18 36.0 35 35.0 31–40 15 30.0 14 28.0 29 29.0 ≥ 41 10 20.0 11 22.0 21 21.0 Total 50 100.0 50 100.0 100 100.0 Mean ± SD 32.1 ± 8.888 31.9 ± 9.181 32.1 ± 9.036 The age distribution of patients in both groups was comparable. In Group N, most patients (34%) were in the 21–30 years age range, followed by 31–40 years (30%). A similar pattern was seen in Group B, where 36% were aged 21–30 years and 28% were aged 31–40 years. The mean age of patients in Group N was 32.1 ± 8.888 years, while in Group B it was 31.9 ± 9.181 years. The t-test value (t = 0.111, P = 0.912) indicates no statistically significant difference between the two groups (p > 0.05), confirming that both groups were comparable in age distribution (Table 1). Table 2: Weight-wise Distribution of Patients Weight (kg) Group N (n=50) % Group B (n=50) % Total (n=100) % ≤ 50 11 22.0 7 14.0 18 18.0 51–60 15 30.0 15 30.0 30 30.0 61–70 16 32.0 24 48.0 40 40.0 > 70 8 16.0 4 8.0 12 12.0 Total 50 100.0 50 100.0 100 100.0 Mean ± SD 60.8 ± 11.7 58.4 ± 9.5 t-value / P-value t = 1.126, P = 0.259 (NS) NS = not significant; S = significant; HS = highly significant; VHS = very highly significant. In Group N, most patients (32%) weighed between 61–70 kg, followed by 30% in the 51–60 kg range. Similarly, in Group B, nearly half of the patients (48%) were in the 61–70 kg range, and 30% weighed between 51–60 kg. The mean weight in Group N was 60.8 ± 11.7 kg, and in Group B it was 58.4 ± 9.5 kg. Statistical analysis using the t-test (t = 1.126, P = 0.259) indicated no significant difference between the two groups (p > 0.05). Thus, both groups were comparable in terms of weight distribution, confirming proper randomization without bias related to body weight (Table 2). Table 3: Surgery-wise Classification of Patients in Both Groups Type of Surgery Group N (n=50) % Group B (n=50) % Total (n=100) % Appendicectomy 26 52.0 25 50.0 51 51.0 Hernioplasty 8 16.0 6 12.0 14 14.0 Tubectomy 7 14.0 9 18.0 16 16.0 Ovarian cystectomy 1 2.0 1 2.0 2 2.0 TAH (Total Abdominal Hysterectomy) 8 16.0 9 18.0 17 17.0 Total 50 100.0 50 100.0 100 100.0 Chi-square (χ²) test χ² = 0.614, P = 0.961 (NS) NS = not significant; S = significant; HS = highly significant; VHS = very highly significant. The types of surgeries performed among both study groups were similar. The most common procedure was appendicectomy, accounting for 52% in Group N and 50% in Group B. Other procedures included hernioplasty (16% vs. 12%), tubectomy (14% vs. 18%), ovarian cystectomy (2% in both groups), and total abdominal hysterectomy (TAH) (16% vs. 18%). Statistical analysis using the Chi-square test (χ² = 0.614, P = 0.961) showed no significant difference in the type of surgeries between the two groups (p > 0.05). This confirms that both groups were comparable regarding the nature of surgical procedures, maintaining baseline homogeneity (Table 3). Table 4: Comparison of Heart Rate (bpm) in Both Groups Time Period Group N (Mean ± SD) Group B (Mean ± SD) t-test value P-value & Significance Before shifting to OT 83.50 ± 5.99 83.72 ± 7.46 t = 0.162 P = 0.871, NS Before subarachnoid block 83.72 ± 5.99 83.94 ± 7.60 t = 0.172 P = 0.863, NS After subarachnoid block 0 minutes 83.91 ± 4.87 84.32 ± 7.46 t = 0.325 P = 0.745, NS 1 minute 84.00 ± 5.30 84.34 ± 7.44 t = 0.793 P = 0.793, NS 3 minutes 84.14 ± 4.77 84.22 ± 7.73 t = 0.006 P = 0.950, NS 5 minutes 83.10 ± 6.54 84.14 ± 7.21 t = 0.174 P = 0.860, NS 15 minutes 84.00 ± 7.01 84.20 ± 6.98 t = 0.143 P = 0.886, NS 30 minutes 83.85 ± 6.15 84.13 ± 6.83 t = 0.215 P = 0.829, NS 45 minutes 83.90 ± 5.33 84.23 ± 6.80 t = 0.270 P = 0.787, NS 60 minutes 84.00 ± 4.26 84.30 ± 6.83 t = 0.272 P = 0.786, NS 75 minutes 84.13 ± 3.93 84.22 ± 7.36 t = 0.076 P = 0.939, NS 90 minutes 83.86 ± 3.73 84.21 ± 7.91 t = 0.283 P = 0.777, NS 105 minutes 83.94 ± 2.87 84.32 ± 5.82 t = 0.435 P = 0.663, NS 120 minutes 84.01 ± 9.05 84.40 ± 5.58 t = 0.259 P = 0.796, NS NS = Not Significant; S = Significant; HS = Highly Significant; VHS = Very Highly Significant. The mean heart rate at all recorded time intervals—before shifting to the operating theatre, before subarachnoid block, and at various intervals after the spinal block—was comparable between Group N and Group B. Throughout the intraoperative period (0 to 120 minutes post-block), there were no statistically significant differences in heart rate between the two groups. The p-values at all time points were greater than 0.05, indicating that both intrathecal nalbuphine and buprenorphine had no significant effect on heart rate when used as adjuvants to hyperbaric bupivacaine. This suggests that both drugs maintained stable hemodynamic profiles, with no clinically relevant bradycardia or tachycardia observed during the study period (Table 4).   Table 5: Comparison of Systolic Blood Pressure (mmHg) in Both Groups Time Period Group N (Mean ± SD) Group B (Mean ± SD) t-test value P-value & Significance Before shifting to OT 123.60 ± 10.03 124.81 ± 7.69 t = 0.667 P = 0.500, NS Before subarachnoid block 122.0 ± 9.90 124.90 ± 8.69 t = 1.234 P = 0.219, NS After subarachnoid block 0 minutes 118.64 ± 7.92 121.30 ± 6.69 t = 1.814 P = 0.073, NS 1 minute 119.68 ± 7.84 122.14 ± 9.01 t = 1.456 P = 0.148, NS 3 minutes 120.88 ± 8.51 122.43 ± 8.99 t = 0.885 P = 0.378, NS 5 minutes 119.58 ± 7.92 120.26 ± 8.94 t = 0.403 P = 0.688, NS 15 minutes 118.64 ± 8.60 120.78 ± 8.87 t = 1.224 P = 0.223, NS 30 minutes 118.26 ± 7.88 121.01 ± 8.62 t = 1.665 P = 0.099, NS 45 minutes 118.86 ± 7.34 121.62 ± 8.45 t = 1.743 P = 0.084, NS 60 minutes 118.44 ± 7.00 120.30 ± 8.31 t = 1.210 P = 0.229, NS 75 minutes 118.18 ± 8.84 120.94 ± 7.95 t = 1.641 P = 0.104, NS 90 minutes 119.03 ± 7.28 121.30 ± 7.76 t = 1.508 P = 0.134, NS 105 minutes 118.44 ± 7.00 120.30 ± 8.31 t = 1.210 P = 0.229, NS 120 minutes 119.03 ± 3.01 120.41 ± 6.67 t = 1.333 P = 0.185, NS NS = Not significant; S = Significant; HS = Highly significant; VHS = Very highly significant. The mean systolic blood pressure (SBP) values recorded at various time intervals before and after administration of spinal anaesthesia were comparable between the two groups. Before shifting to the operating theatre and prior to the subarachnoid block, the SBP values in both groups were nearly identical. After the spinal block, minor fluctuations in systolic pressure were observed in both groups, but these changes were not statistically significant at any interval (p > 0.05). The t-test values at all points indicated no significant intergroup difference, suggesting that both intrathecal nalbuphine and buprenorphine maintained stable systolic blood pressure throughout the intraoperative period. Hence, both drugs demonstrated good hemodynamic stability when used as adjuvants to intrathecal bupivacaine (Table 5). Table 6: Comparison of Diastolic Blood Pressure (mmHg) in Both Groups Time Period Group N (Mean ± SD) Group B (Mean ± SD) t-test value P-value & Significance Before shifting to OT 77.60 ± 8.13 78.64 ± 6.32 t = 0.714 P = 0.476, NS Before subarachnoid block 77.54 ± 7.92 78.34 ± 8.62 t = 0.483 P = 0.630, NS After subarachnoid block 0 minutes 77.33 ± 8.92 78.00 ± 5.63 t = 0.449 P = 0.654, NS 1 minute 77.04 ± 9.44 77.62 ± 9.58 t = 0.304 P = 0.761, NS 3 minutes 77.12 ± 5.49 77.86 ± 6.07 t = 0.639 P = 0.524, NS 5 minutes 77.56 ± 4.09 77.60 ± 5.15 t = 0.043 P = 0.965, NS 15 minutes 77.79 ± 6.54 77.92 ± 4.27 t = 0.117 P = 0.906, NS 30 minutes 77.56 ± 7.83 78.24 ± 8.34 t = 0.420 P = 0.675, NS 45 minutes 77.82 ± 7.02 77.80 ± 6.62 t = 0.014 P = 0.988, NS 60 minutes 77.53 ± 8.95 78.30 ± 4.91 t = 0.533 P = 0.595, NS 75 minutes 78.03 ± 6.97 78.51 ± 7.96 t = 0.320 P = 0.749, NS 90 minutes 78.13 ± 6.12 78.34 ± 8.68 t = 0.139 P = 0.889, NS 105 minutes 78.21 ± 5.35 78.42 ± 6.19 t = 0.182 P = 0.856, NS 120 minutes 78.04 ± 4.84 78.31 ± 6.42 t = 0.237 P = 0.812, NS NS = Not significant; S = Significant; HS = Highly significant; VHS = Very highly significant. The mean diastolic blood pressure (DBP) values at all-time intervals—before and after spinal anaesthesia—were comparable between Group N and Group B. Prior to the subarachnoid block, DBP values were similar in both groups, showing no significant baseline difference. After the block, the diastolic pressures in both groups remained stable with only minor variations throughout the intraoperative period. At all recorded time points (0–120 minutes), the p-values were greater than 0.05, confirming that there was no statistically significant difference in diastolic blood pressure between the two groups. This indicates that both intrathecal nalbuphine and buprenorphine maintained stable diastolic blood pressure levels, contributing to overall hemodynamic stability during lower abdominal surgeries under spinal anaesthesia (Table 6). Table 7: Comparison of SpO₂ (%) in Both Groups Time Period Group N (Mean ± SD) Group B (Mean ± SD) t-test value P-value & Significance Before shifting to OT 99.12 ± 0.938 99.00 ± 0.895 t = 0.654 P = 0.514, NS Before subarachnoid block 99.04 ± 0.836 99.02 ± 0.795 t = 0.122 P = 0.902, NS After subarachnoid block 0 minutes 98.84 ± 1.020 98.94 ± 1.037 t = 0.486 P = 0.628, NS 1 minute 98.86 ± 0.938 99.01 ± 0.947 t = 0.795 P = 0.428, NS 3 minutes 98.82 ± 0.909 98.92 ± 0.918 t = 0.547 P = 0.585, NS 5 minutes 99.00 ± 0.836 99.02 ± 0.795 t = 0.122 P = 0.902, NS 15 minutes 98.94 ± 1.037 98.84 ± 1.020 t = 0.486 P = 0.628, NS 30 minutes 99.21 ± 0.947 98.86 ± 0.938 t = 1.856 P = 0.066, NS 45 minutes 98.92 ± 0.918 98.82 ± 0.909 t = 0.547 P = 0.585, NS 60 minutes 99.02 ± 0.795 99.03 ± 0.836 t = 0.061 P = 0.951, NS 75 minutes 99.00 ± 0.836 99.04 ± 0.795 t = 0.245 P = 0.806, NS 90 minutes 99.06 ± 0.938 99.02 ± 0.895 t = 0.218 P = 0.827, NS 105 minutes 99.20 ± 0.720 99.18 ± 0.660 t = 0.144 P = 0.885, NS 120 minutes 99.12 ± 0.650 99.04 ± 0.730 t = 0.578 P = 0.564, NS NS = Not significant; S = Significant; HS = Highly significant; VHS = Very highly significant. The oxygen saturation (SpO₂) levels remained stable and comparable between Group N (nalbuphine) and Group B (buprenorphine) throughout the study period. Before and after subarachnoid block, mean SpO₂ values were consistently within the normal physiological range (98–99%) in both groups. No episodes of desaturation were noted intraoperatively or postoperatively. Statistical analysis showed no significant difference (p > 0.05) between the two groups at any observed time interval. This confirms that the addition of either nalbuphine or buprenorphine as intrathecal adjuvants did not adversely affect oxygen saturation, demonstrating that both drugs maintain adequate respiratory stability during spinal anaesthesia (Table 7). Table 8: Comparison of Sensory and Motor Block Characteristics Between Both Groups Parameter Group N (Mean ± SD) Group B (Mean ± SD) t-test value P-value & Significance Time for sensory onset at T10 (seconds) 143.6 ± 34.04 143.2 ± 29.06 t = 0.063 P = 0.949, NS Time for maximum sensory level (seconds) 288.8 ± 43.11 289.8 ± 34.22 t = 1.284 P = 0.201, NS Time for onset of motor blockade (seconds) 177.8 ± 19.86 175.92 ± 20.22 t = 0.472 P = 0.640, NS NS = Not significant; S = Significant; HS = Highly significant; VHS = Very highly significant. The onset and progression of sensory and motor blockade were comparable between the two groups. The mean time for sensory onset at T10, time to reach maximum sensory level, and onset of motor block showed no statistically significant difference between Group N (nalbuphine) and Group B (buprenorphine) (all p > 0.05). This indicates that both adjuvants, when combined with intrathecal bupivacaine, produce a similar onset profile and rate of block establishment, ensuring equivalent conditions for the initiation of surgery (Table 8). Table 9: Comparison of Motor Block Characteristics between Both Groups Parameter Group N (n = 50) Group B (n = 50) t-test value P-value & Significance Quality of Motor Blockade (Bromage Scale) Grade 3 32 (64%) 27 (54%) Grade 4 18 (36%) 23 (46%) t = 1.03 P = 0.307, NS Time for Maximum Motor Blockade (minutes) 6.60 ± 0.61 6.52 ± 0.57 t = 0.67 P = 0.49, NS NS = Not significant; S = Significant; HS = Highly significant; VHS = Very highly significant. Both nalbuphine (Group N) and buprenorphine (Group B) produced comparable motor block quality and progression when administered intrathecally with hyperbaric bupivacaine. A majority of patients in both groups achieved Grade 3 or Grade 4 motor block, providing adequate muscle relaxation for lower abdominal surgeries. The mean time to reach maximum motor block was nearly identical in both groups (≈ 6.5 minutes), and the difference was not statistically significant (P > 0.05). Table 10: Duration of Surgery in Both Groups Duration (minutes) Group N (n=50) % Group B (n=50) % 30–60 7 14.0 9 18.0 61–90 25 50.0 25 50.0 91–120 18 36.0 16 32.0 Total 50 100.0 50 100.0 Mean ± SD 87.8 ± 23.62 84.8 ± 25.45 t-test value t = 0.61 P = 0.54, NS NS = Not significant; S = Significant; HS = Highly significant; VHS = Very highly significant. The mean duration of surgery in Group N (nalbuphine) was 87.8 ± 23.62 minutes, while in Group B (buprenorphine) it was 84.8 ± 25.45 minutes. Most surgeries in both groups lasted between 61–90 minutes (50% each), followed by 91–120 minutes in 36% of Group N and 32% of Group B. Statistical analysis revealed no significant difference in the duration of surgery between the two groups (t = 0.61, P = 0.54). This confirms that the operative duration was comparable in both groups, ensuring that differences in postoperative analgesia or block characteristics were not influenced by surgical time (Table 10). Table 11: Comparison of VAS Score Between Both Groups Postoperative Pain Assessment (VAS Score) Group N (Mean ± SD) Group B (Mean ± SD) t-test Value P-value & Significance 1st hour 0.60 ± 0.466 0.20 ± 0.340 t = 4.945 P < 0.0001, VHS 1 hour 30 min 1.20 ± 0.438 0.52 ± 0.496 t = 7.267 P < 0.0001, VHS 2nd hour 1.90 ± 0.574 1.11 ± 0.616 t = 6.635 P < 0.0001, VHS 3rd hour 2.56 ± 0.547 1.56 ± 0.458 t = 9.911 P < 0.0001, VHS 4th hour 3.23 ± 0.471 2.30 ± 0.483 t = 9.748 P < 0.0001, VHS 5th hour 3.82 ± 0.491 2.91 ± 0.400 t = 10.160 P < 0.0001, VHS 6th hour 4.00 ± 0.437 3.61 ± 0.438 t = 4.457 P < 0.0001, VHS 7th hour 4.00 ± 0.438 0.00 ± 0.438 t = 45.714 P < 0.0001, VHS NS = Not significant; S = Significant; HS = Highly significant; VHS = Very highly significant. The postoperative pain scores measured by the Visual Analog Scale (VAS) were significantly different between the two groups throughout the observation period. In Group N (nalbuphine), the VAS scores showed an earlier and steeper rise, indicating shorter duration of analgesia. In contrast, Group B (buprenorphine) maintained lower pain scores for a prolonged period, reflecting longer-lasting postoperative analgesia. From the 1st hour through the 6th hour, patients in Group B consistently reported lower VAS scores compared to Group N, with all differences being very highly significant (P < 0.0001). By the 7th hour, most patients in Group N had already required rescue analgesia, while Group B patients continued to have effective pain relief. These findings indicate that intrathecal buprenorphine provides superior and longer-lasting postoperative analgesia compared to intrathecal nalbuphine when both are used as adjuvants to hyperbaric bupivacaine for lower abdominal surgeries (Table 11). Table 12: Comparison of Duration and Time of Rescue Analgesia Between Both Groups Parameter Group N (Mean ± SD) Group B (Mean ± SD) t-test value P-value & Significance Duration of Analgesia (minutes) 297.14 ± 75.46 379.8 ± 95.2 t = 4.81 P < 0.0001, VHS Time of Rescue Analgesia (minutes) 342.2 ± 39.73 418.9 ± 40.43 t = 9.56 P < 0.0001, VHS NS = Not significant; S = Significant; HS = Highly significant; VHS = Very highly significant. The mean duration of postoperative analgesia was 297.14 ± 75.46 minutes in Group N (nalbuphine) and 379.8 ± 95.2 minutes in Group B (buprenorphine). Similarly, the mean time to first rescue analgesia was 342.2 ± 39.73 minutes in Group N and 418.9 ± 40.43 minutes in Group B. Both parameters showed very highly significant differences between the two groups (P < 0.0001), indicating that intrathecal buprenorphine provided a longer duration of analgesia and delayed the need for rescue analgesic compared to intrathecal nalbuphine. These findings confirm that buprenorphine offers superior, prolonged, and more consistent postoperative pain relief, reducing the requirement for additional analgesic doses and improving overall patient comfort in the postoperative period (Table 12).

This study compared intrathecal nalbuphine (0.8 mg) and buprenorphine (60 µg) as adjuvants to 0.5% hyperbaric bupivacaine in 100 ASA I–II patients undergoing lower abdominal surgeries under spinal anaesthesia. Both groups were similar in demographics and baseline characteristics. The study evaluated sensory and motor block profiles, duration of analgesia, hemodynamic stability, and side effects. Spinal anaesthesia provides effective intraoperative conditions but limited postoperative analgesia. The addition of intrathecal opioids like nalbuphine and buprenorphine extends analgesia without significant respiratory depression. Both are mixed agonist–antagonist opioids nalbuphine acting as a κ-agonist and μ-antagonist, and buprenorphine as a partial μ-agonist and κ-antagonist providing effective pain control with minimal adverse effects. In this study, no significant variations were observed in heart rate, systolic or diastolic blood pressure, or oxygen saturation between the groups, consistent with earlier findings [9, 10]. This confirms that both agents maintain stable hemodynamics when administered intrathecally. The onset times for sensory (≈143 sec) and motor blockade (≈176 sec) were nearly identical in both groups (p > 0.05), comparable with results by Mukherjee et al. [11 and Uday Prathap et al. [12]. The maximum sensory level (T6) was achieved at similar times, aligning with most previous studies. The quality of motor block (Bromage grades 3–4) was also comparable across both groups. Postoperatively, buprenorphine provided significantly lower VAS scores up to 7 hours, indicating better analgesic quality. The mean duration of analgesia was longer with buprenorphine (379.8 ± 95.2 min) compared to nalbuphine (297.14 ± 75.46 min), a difference that was highly significant (p < 0.0001). These findings concur with those of earlier studies [2, 12]. Similarly, the mean time to rescue analgesia was significantly prolonged with buprenorphine (418.9 ± 40.43 min) versus nalbuphine (342.2 ± 39.73 min), supporting previous observations by Rudra A [13], and Thomas W [14]. No adverse effects such as hypotension, bradycardia, nausea, or respiratory depression were observed in either group, reaffirming findings by Culebras X et al. [15].

In conclusion, both nalbuphine and buprenorphine are safe, effective intrathecal adjuvants, providing stable hemodynamics and satisfactory anaesthesia. However, buprenorphine offers longer and superior postoperative analgesia, delayed need for rescue medication, and better pain control, making it a preferable adjuvant for lower abdominal surgeries.

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