A hernia is defined as a protrusion of a viscus or part of a viscus through a defect in the wall of its containing cavity [1]. Factors that increase intra-abdominal pressure, such as strenuous physical activity, obesity, chronic cough, and constipation, are well-established predisposing factors for abdominal wall hernias [2,3]. Inguinal hernias are the most common type, accounting for approximately 75% of all abdominal wall hernias, with a profound male predominance [4,5]. If left untreated, hernias can lead to serious complications, including irreducibility, incarceration, and life-threatening strangulation [6]. Surgical repair is the definitive treatment for symptomatic hernias. Spinal anesthesia is a widely favored technique for lower abdominal surgeries like herniorrhaphy, offering excellent operating conditions, a favorable safety profile, and facilitation of early recovery [7,8]. To improve the quality and duration of anesthesia and postoperative analgesia, opioids are frequently added as adjuvants to local anesthetics like bupivacaine [9]. Among the commonly used opioid adjuvants, fentanyl is a potent, lipophilic agonist known for its rapid onset of action and its ability to prolong sensory analgesia without significantly extending motor block or causing delayed respiratory depression [10,11]. Pethidine, a synthetic opioid, possesses both opioid agonist and local anesthetic properties, which can contribute to extended postoperative pain control [12,13]. While systematic reviews have confirmed the benefit of adding opioid adjuvants to intrathecal local anesthetics for improving block quality and postoperative analgesia [9], there is a scarcity of direct, head-to-head comparisons between intrathecal pethidine and fentanyl specifically for herniorrhaphy. This study was designed to address this gap by prospectively evaluating the comparative efficacy and safety of these two adjuvants when combined with bupivacaine.

Study Design This was a prospective, randomized, double-blind, single-center comparative study conducted at a tertiary care teaching hospital in Jaipur, India, over an 18-month period. Ethical approval was obtained from the Institutional Ethics Committee (Ref: IEC/P-214/2023), and the trial was registered with the appropriate clinical trials registry. Participants Seventy-two adult patients of ASA physical status I or II, aged 18 to 60 years, scheduled for elective unilateral herniorrhaphy under spinal anesthesia were enrolled. Written, informed consent was obtained from all participants. Exclusion criteria included patient refusal, known allergy to study medications, contraindications to neuraxial blockade (e.g., coagulopathy, local infection, severe hypovolemia), and the inability to comprehend the Visual Analogue Scale (VAS) for pain assessment. Randomization and Blinding Patients were randomly allocated into one of two groups (n=36 each) using a computer-generated random number table. The allocation was concealed using sealed, opaque envelopes, which were opened in the operating theatre just before the preparation of the study drug. The study was double-blinded; the patients, the attending anesthesiologist performing the block, and the postoperative assessor collecting the data were all unaware of the group allocation. A separate anesthesiologist, not involved in patient care or data collection, prepared the study solutions. Interventions Upon arrival in the operating room, standard monitoring was established, including electrocardiography (ECG), non-invasive blood pressure (NIBP), and pulse oximetry (SpO2). An intravenous line was secured, and all patients were preloaded with 10 mL/kg of Ringer's lactate solution. Under strict aseptic precautions, a lumbar puncture was performed at the L3-L4 interspace in the sitting position using a 25-gauge Quincke spinal needle. After confirming the free flow of cerebrospinal fluid, patients received one of the following solutions: • Group B+F (Bupivacaine + Fentanyl): 2.5 mL of 0.5% hyperbaric bupivacaine (12.5 mg) + 0.5 mL of fentanyl (25 mcg), for a total volume of 3.0 mL. • Group B+P (Bupivacaine + Pethidine): 2.5 mL of 0.5% hyperbaric bupivacaine (12.5 mg) + 0.5 mL of pethidine (25 mg), for a total volume of 3.0 mL. Outcome Measures Primary Outcomes: 1. Duration of effective analgesia: Time from intrathecal injection to the first request for rescue analgesia (defined as a VAS score ≥ 4). 2. Onset and duration of sensory block: Assessed bilaterally by loss of sensation to pinprick. Onset was the time to reach the T10 dermatome. Duration was the time until two-segment regression from the peak block height. 3. Onset and duration of motor block: Assessed using the Bromage scale (0=no block, 3=complete block). Onset was the time to reach Bromage score 3. Duration was the time to regress to Bromage score 0. Secondary Outcomes: 1. Hemodynamic parameters: Heart rate (HR) and mean arterial pressure (MAP) were recorded at baseline and then every 2 minutes for the first 20 minutes, followed by 5-minute intervals. 2. Intraoperative complications: Hypotension (defined as a >25% decrease in MAP from baseline), bradycardia (HR < 50 bpm), nausea, vomiting, and hypothermia were recorded. 3. Postoperative pain: Assessed using a 10-point VAS at 2, 4, 6, 12, and 24 hours post-block. Statistical Analysis Data were compiled and analyzed using SPSS Statistics for Windows, Version 28.0 (IBM Corp., Armonk, NY). Continuous data were presented as mean ± standard deviation (SD) and compared using the independent samples t-test or Mann-Whitney U test where appropriate. Categorical data were presented as frequencies or percentages and compared using the chi-square test or Fisher's exact test. A p-value of less than 0.05 was considered statistically significant.

Demographic and Baseline Characteristics The two study groups were well-matched with respect to age, gender distribution, and Body Mass Index (BMI). There were no statistically significant differences in these baseline characteristics, ensuring comparability between the groups (Table 1). Table 1: Demographic Characteristics of Study Participants Variable Group B+P (n=36) Group B+F (n=36) p-value Age (years, mean ± SD) 39.41 ± 10.79 40.56 ± 12.74 0.691 Male:Female ratio (%) 63.9 : 36.1 77.8 : 22.2 0.198 BMI (kg/m2, mean ± SD) 23.41 ± 2.10 23.90 ± 2.71 0.394 Legend: Data are presented as mean ± standard deviation or percentage. BMI = Body Mass Index. Intraoperative Hemodynamics There were no clinically significant differences in mean arterial blood pressures or heart rates between the groups throughout the intraoperative period, with the exception of transient episodes of tachycardia observed at 10 and 20 minutes post-injection in Group B+F, which resolved spontaneously. However, the incidence of hypotension was significantly higher in the pethidine group. Hypotension occurred in 19 patients (52.8%) in Group B+P, compared to only 2 patients (5.6%) in Group B+F (p<0.001). Sensory Block, Motor Block, and Postoperative Analgesia The combination of bupivacaine and fentanyl resulted in a significantly longer duration of effective analgesia and prolonged sensory and motor blockade compared to the bupivacaine and pethidine combination. The mean postoperative VAS score was also significantly lower in the fentanyl group (Table 2). Table 2: Analgesic and Block Characteristics Parameter Group B+P (n=36) Group B+F (n=36) p-value Duration of effective analgesia (min) 240.44 ± 21.20 288.19 ± 73.23 0.002 Duration of sensory block (min) 234.33 ± 33.27 273.17 ± 61.38 0.001 Duration of motor block (min) 195.0 ± 11.62 228.39 ± 42.25 <0.001 VAS pain score at first request for analgesia (mean ± SD) 4.61 ± 0.97 3.74 ± 0.89 <0.001 Legend: Data are presented as mean ± standard deviation. VAS = Visual Analogue Scale. Intraoperative and Postoperative Events The overall incidence of intraoperative adverse events was significantly lower in the fentanyl group. Besides the marked difference in hypotension, the incidence of other events like hypothermia and nausea/vomiting was low and comparable between the groups (Table 3). No patient in either group experienced severe adverse events such as respiratory depression, excessive sedation, or neurological deficits. Table 3: Incidence of Intraoperative Adverse Events Event Group B+P (%) Group B+F (%) p-value Hypotension 19 (52.8%) 2 (5.6%) <0.001 Hypothermia 3 (8.3%) 4 (11.1%) 0.686 Nausea/Vomiting 2 (5.6%) 2 (5.6%) 1.000 No Event 12 (33.3%) 28 (77.8%) <0.001 Legend: Data are presented as count (percentage).

This randomized, double-blinded study demonstrates that the addition of 25 mcg of fentanyl to 12.5 mg of intrathecal bupivacaine provides a significantly longer duration of postoperative analgesia compared to 25 mg of pethidine for patients undergoing herniorrhaphy. This primary finding is consistent with previous research indicating the potent synergistic effect of lipophilic opioids like fentanyl when combined with local anesthetics [9,14,15]. The prolonged analgesia observed in the fentanyl group translates to delayed requests for rescue medication and lower postoperative pain scores, contributing to enhanced patient comfort [16,17]. A key secondary finding of this study was the superior hemodynamic stability observed in the fentanyl group. The incidence of hypotension was nearly ten times higher in the pethidine group (52.8% vs. 5.6%). This finding aligns with studies that have highlighted the dose-sparing effect of fentanyl, which can reduce the required bupivacaine dose and its associated sympathetic blockade [18,19]. Conversely, pethidine itself can cause vasodilation and has a more pronounced effect on sympathetic tone at the doses required for effective analgesia, potentially explaining the higher incidence of hypotension observed in Group B+P [13,20]. The prolonged durations of both sensory and motor block in the fentanyl group further underscore its superior profile as an adjuvant. These results are in concordance with studies by Bindra et al. and Bano et al., who also reported longer-lasting blocks with intrathecal fentanyl compared to other adjuvants [21,22]. While a prolonged motor block can sometimes be undesirable, the duration observed in this study did not delay patient discharge or lead to complications, and was accompanied by a much longer period of effective pain relief. The overall safety profile of both combinations was excellent, with no major adverse events recorded. The incidences of minor side effects such as nausea, vomiting, and hypothermia were low and did not differ significantly between the groups, corroborating the general safety of low-dose intrathecal opioids as documented in other studies [23,24]. Limitations This study has some limitations. First, it was conducted at a single center, which may limit the generalizability of the findings. Second, the sample size was modest, although it was sufficient to detect statistically significant differences in the primary outcomes. Finally, our follow-up was focused on the early postoperative period, and a longer-term assessment could provide further insights into patient satisfaction and recovery milestones.

In patients undergoing elective herniorrhaphy under spinal anesthesia, the combination of intrathecal bupivacaine with 25 mcg of fentanyl achieves a more prolonged and effective duration of postoperative analgesia, longer sensory and motor blockade, and a significantly better safety profile with respect to hemodynamic stability when compared to 25 mg of pethidine. Based on these findings, the routine use of fentanyl as an adjuvant to bupivacaine is recommended to optimize postoperative pain management and enhance recovery in this patient population [11,20].

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