Spinal anesthesia has long been the anesthetic technique of choice for infraumbilical, lower limb, gynecological, and urological surgeries due to its rapid onset, reliability, and cost-effectiveness. It involves deposition of local anesthetic agents in the subarachnoid space, producing profound sensory and motor block by interrupting nerve conduction at the spinal cord level.1,2 Bupivacaine, a long-acting amide local anesthetic, is commonly used for spinal anesthesia owing to its stable hemodynamic profile and extended duration of block compared to lignocaine.3 However, its limitation lies in the relatively short duration of postoperative analgesia, necessitating the addition of intrathecal adjuvants to enhance block quality and duration. Clonidine, an α2-adrenergic receptor agonist, has been widely explored as an intrathecal adjuvant. Its mechanism of action includes inhibition of nociceptive neurotransmitter release and hyperpolarization of post-synaptic dorsal horn neurons.4 Intrathecal clonidine augments both sensory and motor block and provides dose-dependent analgesia, but side effects such as hypotension, bradycardia, and sedation may limit its routine use.5 Fentanyl, a potent lipophilic opioid, is another commonly used intrathecal adjuvant. It binds to μ-opioid receptors in the dorsal horn, enhancing analgesia without prolonging motor blockade.6 Due to its lipophilicity, fentanyl provides rapid onset of action and minimal cephalad spread, thereby reducing the risk of delayed respiratory depression seen with hydrophilic opioids like morphine.7 However, adverse effects such as pruritus, nausea, and urinary retention are noted.8 Previous comparative studies have yielded conflicting results regarding the superiority of clonidine or fentanyl when added to bupivacaine. Some suggest clonidine provides longer-lasting analgesia,9 whereas others emphasize fentanyl’s faster onset and hemodynamic stability.10 Given these varying reports, this study aims to systematically compare the clinical profiles of patients undergoing spinal anesthesia with intrathecal bupivacaine combined with clonidine versus fentanyl. The primary objectives were to compare onset and duration of sensory and motor blockade, while secondary outcomes included intraoperative hemodynamic stability, sedation, and adverse effects. The findings will guide anesthesiologists in selecting the appropriate adjuvant tailored to individual patient profiles and surgical requirements.

A prospective, randomized, controlled study was conducted at a tertiary care teaching hospital over 12 months after obtaining Institutional Ethical Committee approval and informed patient consent. Study Population A total of 100 patients, ASA I–II, aged 18–60 years, undergoing elective infraumbilical or lower limb surgeries were recruited. Inclusion criteria: • ASA I and II patients • Age 18–60 years • Elective infraumbilical/lower limb surgery under spinal anesthesia • Consent obtained Exclusion criteria: • Contraindications to spinal anesthesia • Known hypersensitivity to study drugs • Severe cardiovascular, renal, or hepatic disease • Neurological or psychiatric disorders • Pregnancy or lactation Randomization and Grouping Patients were randomized into two equal groups (n=50 each): • Group C (Clonidine): 3 mL (15 mg) of 0.5% hyperbaric bupivacaine + clonidine 30 μg • Group F (Fentanyl): 3 mL (15 mg) of 0.5% hyperbaric bupivacaine + fentanyl 25 μg Procedure All patients underwent preoperative evaluation and received preloading with 10 mL/kg of Ringer’s lactate. Spinal anesthesia was performed in the sitting position using a 25G Quincke needle at L3–L4 interspace. After drug administration, patients were positioned supine. Observations Recorded • Onset of sensory block: Time to achieve T10 level • Duration of sensory block: Regression to S1 • Onset and duration of motor block: Modified Bromage scale • Hemodynamic monitoring: Heart rate, systolic/diastolic/mean arterial pressure, oxygen saturation • Sedation score: Ramsay Sedation Scale • Adverse effects: Hypotension, bradycardia, nausea, vomiting, pruritus, respiratory depression Statistical Analysis Sample size was calculated based on prior studies expecting 20% difference in block duration (power 80%, alpha 0.05). Continuous data were expressed as mean ± SD and compared using Student’s t-test; categorical variables were compared using Chi-square test. A p value <0.05 was considered significant.

Table 1. Demographic Characteristics Parameter Group C (n=50) Group F (n=50) p-value Age (years, mean ± SD) 38.2 ± 9.1 37.6 ± 8.7 0.71 Gender (M/F) 28/22 30/20 0.67 ASA I/II 32/18 34/16 0.58 Both groups were comparable in demographic characteristics. Table 2. Block Characteristics Variable Group C Group F p-value Onset of sensory block (min) 4.8 ± 1.1 3.6 ± 0.9 0.001 Duration of sensory block (min) 210 ± 25 165 ± 20 <0.001 Onset of motor block (min) 5.2 ± 1.0 4.0 ± 1.2 0.002 Duration of motor block (min) 180 ± 20 140 ± 18 <0.001 Fentanyl provided faster onset, clonidine prolonged duration. Table 3. Hemodynamic Parameters Variable Group C Group F p-value Incidence of hypotension (%) 24% 12% 0.05 Incidence of bradycardia (%) 16% 8% 0.12 Hypotension and bradycardia were more common with clonidine. Table 4. Sedation Score (Ramsay Scale) Sedation Score Group C (%) Group F (%) 2 52 84 3 36 12 4 12 4 Clonidine caused higher sedation. Table 5. Adverse Events Adverse Event Group C (%) Group F (%) Nausea/Vomiting 8 10 Pruritus 0 18 Respiratory depression 0 0 Fentanyl was associated with pruritus. Table 6. Patient Satisfaction Score Score (1–5) Group C Group F p-value 4.3 ± 0.6 4.5 ± 0.5 0.19 Both groups showed high satisfaction, slightly higher in fentanyl group.

This study compared the clinical profile of intrathecal bupivacaine with clonidine and fentanyl. The findings revealed that clonidine significantly prolonged the duration of both sensory and motor block, while fentanyl ensured faster onset and stable intraoperative hemodynamics. Our results align with Singh et al.11 who reported that clonidine prolonged block duration by 30–40% compared with fentanyl. Similarly, Sharma et al.12 observed greater sedation with clonidine due to central α2 action. Conversely, fentanyl has been repeatedly associated with faster onset, as shown by Gupta et al.13, which is consistent with our findings. Hemodynamic instability remains a concern with clonidine, as reported by Dinesh et al.14, who noted higher incidences of bradycardia and hypotension. Our study also demonstrated more frequent hypotension in the clonidine group, necessitating vigilant monitoring. Fentanyl’s adverse effect profile primarily included pruritus, a finding corroborated by Desai et al.15 and Kumar et al.16. However, no respiratory depression was observed, consistent with the low doses typically employed intrathecally. Patient satisfaction scores were comparable across both groups, though slightly higher in the fentanyl group. This echoes the work of Patel et al.17 who concluded that fentanyl provides greater patient comfort during shorter-duration procedures. Overall, clonidine may be more suitable for longer surgical durations where prolonged postoperative analgesia is desired, whereas fentanyl is preferable for short-duration surgeries and patients with cardiovascular comorbidities.

Intrathecal clonidine prolongs sensory and motor block but increases the risk of sedation and hemodynamic disturbances. Fentanyl, on the other hand, ensures faster onset, hemodynamic stability, and high patient satisfaction but is associated with pruritus. Both agents are effective adjuvants, and their selection should be tailored to patient condition, surgical duration, and anticipated analgesic needs.

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