Spinal anaesthesia is widely used for urological procedures because it is technically simple, economical, provides rapid and reliable sensory and motor blockade, and allows the patient to remain conscious during surgery. It may also facilitate early recognition of complications during transurethral procedures. However, spinal anaesthesia with a local anaesthetic alone has limitations, including a finite duration of surgical anaesthesia and inadequate postoperative analgesia. Levobupivacaine, the pure S(−)-enantiomer of bupivacaine, produces effective spinal anaesthesia with sensory and motor block characteristics comparable to racemic bupivacaine, while having a comparatively favourable cardiovascular and neurological safety profile [1]. This is particularly relevant in urological patients, many of whom are elderly and may have associated comorbidities. Intrathecal adjuvants are therefore added to local anaesthetics to improve block quality, prolong anaesthesia and postoperative analgesia, and reduce the required local-anaesthetic dose. Fentanyl is a highly lipid-soluble, selective μ-opioid receptor agonist that acts synergistically with intrathecal local anaesthetics. It accelerates sensory-block onset and improves intraoperative and postoperative analgesia without producing substantial sympathetic or motor blockade. Nevertheless, fentanyl may cause adverse effects such as pruritus, nausea, vomiting, urinary retention and respiratory depression. Studies have demonstrated that the addition of fentanyl to intrathecal levobupivacaine improves the onset and duration of sensory and motor blockade and prolongs postoperative analgesia [2]. Dexmedetomidine is a highly selective α₂-adrenoceptor agonist with analgesic, sedative and sympatholytic properties. Its intrathecal action is mediated through inhibition of nociceptive neurotransmitter release and hyperpolarisation of neurons in the spinal dorsal horn. Unlike opioids, dexmedetomidine generally does not cause clinically significant respiratory depression. Intrathecal dexmedetomidine has been shown to hasten the onset and prolong the duration of sensory and motor blockade produced by levobupivacaine [3]. Comparative studies have reported that dexmedetomidine provides a longer sensory block, motor block and pain-free period than fentanyl, although it may be associated with bradycardia, hypotension and sedation [4,5].

AIM

To compare the efficacy and safety of intrathecal dexmedetomidine versus fentanyl as adjuvants to isobaric levobupivacaine for spinal anaesthesia in patients undergoing elective urological surgeries.

OBJECTIVES

1. To compare the onset, maximum level, two-segment regression and total duration of sensory blockade between the LD and LF groups.
2. To compare the onset, intensity and duration of motor blockade and the duration of postoperative analgesia between the two groups.
3. To compare perioperative haemodynamic parameters, sedation and adverse effects between the two groups.

Source of Data The study data were obtained from adult patients scheduled to undergo elective urological surgeries under spinal anaesthesia at Vivekananda Polyclinic and Institute of Medical Sciences, Lucknow, Uttar Pradesh. Patients satisfying the eligibility criteria were enrolled after approval from the Institutional Ethics Committee and after obtaining written informed consent. Clinical information was collected through history, pre-anaesthetic examination, intraoperative monitoring and postoperative follow-up. Study Design The study was a prospective, randomized, double-blind, two-group comparative clinical study. Study Location The study was conducted in the operation theatre complex and postoperative recovery area of Vivekananda Polyclinic and Institute of Medical Sciences, Lucknow, Uttar Pradesh. Study Duration The study was conducted over 12 months, from 1 June 2015 to 31 May 2016. Study Population The study included adult patients of either sex, aged 20–70 years, belonging to American Society of Anesthesiologists Physical Status (ASA-PS) grades I or II and scheduled for elective urological surgery under spinal anaesthesia. Sample Size A total of 70 patients were studied and allocated equally into two groups: • Group LD (n=35): Patients received 12.5 mg of 0.5% isobaric levobupivacaine (2.5 mL) with 5 µg dexmedetomidine diluted with preservative-free normal saline to 0.5 mL. The total intrathecal volume was 3.0 mL. • Group LF (n=35): Patients received 12.5 mg of 0.5% isobaric levobupivacaine (2.5 mL) with 25 µg fentanyl (0.5 mL). The total intrathecal volume was 3.0 mL. The sample size was based on a previous study reporting mean sensory-block durations of 73.9±13.9 minutes with dexmedetomidine and 64.9±11.3 minutes with fentanyl. Considering an expected difference of approximately 9 minutes, a pooled standard deviation of approximately 12.6 minutes, 80% power and a 5% two-sided significance level, the protocol estimated a minimum requirement of approximately 29 patients per group. After allowing for possible attrition or incomplete observations, 35 patients were included in each group. Sampling Technique and Randomization Eligible patients were enrolled consecutively until the required sample size was reached. The 70 participants were randomly allocated in a 1:1 ratio to Group LD or Group LF using a computer-generated random-number sequence. The study solution was prepared by an anaesthesiologist who was not involved in administering spinal anaesthesia, assessing the block or collecting outcome data. The anaesthesiologist administering the intrathecal drug and recording study outcomes remained unaware of group allocation. Both preparations had an identical total volume of 3.0 mL. Inclusion Criteria 1. Patients aged 20–70 years. 2. Patients of either sex. 3. ASA-PS grade I or II. 4. Patients scheduled for elective urological surgery under spinal anaesthesia. 5. Patients who provided written informed consent. Exclusion Criteria 1. Age below 20 years or above 70 years. 2. ASA-PS grade III or IV. 3. Body weight below 30 kg or above 80 kg, as specified in the study protocol. 4. Body mass index greater than 35 kg/m². 5. Height below 150 cm or above 185 cm. 6. Severe cardiovascular or cerebrovascular disease. 7. Uncontrolled diabetes mellitus or chronic renal failure. 8. Any contraindication to spinal anaesthesia, including patient refusal, local infection, coagulation abnormality or severe hypovolaemia. 9. History of chronic analgesic therapy. 10. Known hypersensitivity to amide-type local anaesthetics, dexmedetomidine or fentanyl. 11. Patients who were uncooperative or unable to understand the pain-assessment scale. Pre-Anaesthetic Evaluation A detailed history was obtained, and general and systemic examinations were performed. Routine investigations included haemoglobin estimation, blood grouping, blood glucose, blood urea, serum creatinine and coagulation profile. Electrocardiography and other investigations were performed when clinically indicated. Baseline pulse rate, respiratory rate, systolic and diastolic blood pressures and oxygen saturation were recorded. Patients were informed about spinal anaesthesia, the Visual Analogue Scale (VAS), postoperative monitoring and rescue analgesia. Written informed consent was obtained, and all patients were kept fasting for eight hours before surgery. Procedure and Methodology On arrival in the operation theatre, standard monitoring consisting of electrocardiography, non-invasive blood pressure and pulse oximetry was instituted. Three initial measurements were obtained, and their average was considered the baseline value. An intravenous line was secured, and the patient was preloaded with an appropriate crystalloid solution at approximately 10 mL/kg over 20 minutes. Under strict aseptic precautions, lumbar puncture was performed at the L3–L4 interspace with the patient in the sitting position using a 25-gauge Quincke spinal needle. After confirming free flow of clear cerebrospinal fluid, the allocated 3.0-mL study solution was injected intrathecally at an approximate rate of 1 mL every three seconds. The operating table was kept horizontal, and the patient was immediately placed in the supine position. Assessment of sensory blockade Sensory blockade was assessed bilaterally using the pinprick method with a 22-gauge hypodermic needle. Assessments were made every two minutes until the level stabilised. The following measurements were recorded: • Time from completion of injection to attainment of sensory block at T12. • Time to attainment of T10 sensory level. • Highest sensory level achieved. • Time required to attain the highest sensory level. • Time required for two-segment regression from the highest level. • Time required for sensory regression to the S1 dermatome. Assessment of motor blockade Motor blockade was evaluated using the Modified Bromage Scale: • Grade 0: no motor paralysis. • Grade 1: unable to raise the extended leg. • Grade 2: unable to flex the knee. • Grade 3: unable to flex the ankle. The time of onset of motor block, time to maximum motor blockade, maximum Bromage grade and time to complete motor recovery (Bromage grade 0) were recorded. Haemodynamic and respiratory monitoring Heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure, respiratory rate and oxygen saturation were recorded at baseline and at 2, 5, 10, 15, 20, 25, 30, 40, 50, 60, 90, 120, 150, 180, 240, 300 and 360 minutes. Hypotension was defined as a reduction in systolic blood pressure of more than 20% from baseline or an absolute systolic blood pressure below 90 mmHg. It was managed with intravenous fluids and incremental intravenous mephentermine or ephedrine, when required. Bradycardia was defined as a heart rate below 50 beats/minute and was treated with atropine 0.6 mg intravenously. Postoperative analgesia Postoperative pain was evaluated using a 0–10 VAS, where 0 indicated no pain and 10 indicated the worst imaginable pain. Pain assessment was continued for the first six postoperative hours. Duration of analgesia was defined as the interval from intrathecal injection to the first request for rescue analgesia. Intramuscular diclofenac 75 mg was administered when the VAS score exceeded 5 or when the patient requested analgesia. Sedation and adverse effects Sedation was evaluated using the Modified Wilson Sedation Scale. Patients were observed for hypotension, bradycardia, nausea, vomiting, shivering, pruritus, respiratory depression, excessive sedation and other complications. Postoperative surveillance was continued for 24 hours. Sample Processing No biological specimen was collected specifically for the research intervention; therefore, research-specific sample processing, storage or disposal was not applicable. Blood samples required for routine preoperative investigations were collected aseptically, labelled with the patient’s identification details and processed in the institutional laboratory according to standard hospital procedures. The study primarily involved clinical, anaesthetic and physiological observations. Data Collection Data were recorded prospectively in a structured case-record form and subsequently entered into the master chart. The collected variables included: • Demographic and baseline variables: age, sex, ASA grade, height, weight and BMI. • Clinical variables: diagnosis, type of urological surgery and duration of surgery. • Sensory-block characteristics. • Motor-block characteristics and Modified Bromage grade. • Duration of analgesia and serial postoperative VAS scores. • Serial heart rate, blood-pressure, respiratory-rate and SpO₂ measurements. • Sedation scores. • Rescue medication and management of haemodynamic changes. • Intraoperative and postoperative adverse effects. Each participant was assigned a study identification number. Data were checked for completeness and consistency before statistical analysis. Statistical Methods Data were analysed using SPSS for Windows, version 17.0. Continuous variables were summarised as mean and standard deviation, while categorical variables were presented as frequencies and percentages. The independent-samples Student’s t test was used to compare normally distributed continuous variables between the LD and LF groups. The Mann–Whitney U test was considered for continuous or ordinal variables that did not satisfy normality assumptions. Categorical variables were compared using the chi-square test or Fisher’s exact test when expected cell frequencies were small. Serial haemodynamic measurements were compared between the groups at the predefined time points; changes over time could additionally be evaluated using repeated-measures analysis. Pearson’s correlation was used for normally distributed variables, while Spearman’s rank correlation was used for ordinal or non-normally distributed variables. All tests were two-tailed, and p<0.05 was considered statistically significant. Effect estimates were reported with 95% confidence intervals wherever applicable.

Table 1: Overall comparative efficacy and safety of intrathecal dexmedetomidine versus fentanyl as adjuvants to isobaric levobupivacaine (N=70)

Table 1 presents the overall comparative efficacy and safety of intrathecal dexmedetomidine and fentanyl as adjuvants to isobaric levobupivacaine. The onset of sensory block at T12 was significantly faster in Group LD than in Group LF (1.54±0.51 versus 2.51±0.51 minutes), with a mean difference of −0.97 minutes (95% CI: −1.21 to −0.73; t=−8.03, p<0.001). Group LD also demonstrated significantly longer sensory blockade (258.29±15.81 versus 169.71±6.41 minutes; MD=88.57 minutes, 95% CI: 82.82–94.33; p<0.001), motor blockade (204.86±11.47 versus 132.57±5.99 minutes; MD=72.29 minutes, 95% CI: 67.92–76.65; p<0.001) and postoperative analgesia (236.57±16.17 versus 147.86±5.98 minutes; MD=88.71 minutes, 95% CI: 82.90–94.53; p<0.001). The mean VAS score at four hours was significantly lower in Group LD (2.97±0.66) than in Group LF (3.37±0.55), with a mean difference of −0.40 (95% CI: −0.69 to −0.11; p=0.008). However, grade 2 sedation was significantly more frequent in Group LD than Group LF (28.6% versus 2.9%; OR=13.60, 95% CI: 1.63–113.25; p=0.003). The incidence of any adverse effect other than sedation was higher in Group LD (20.0%) than Group LF (11.4%), but this difference was not statistically significant (OR=1.94, 95% CI: 0.51–7.33; p=0.325).

Table 2: Comparison of sensory-block characteristics between the LD and LF groups (N=70)

Table 2 compares the sensory-block characteristics between the two groups. The onset of sensory block at T12 was significantly faster in Group LD than Group LF (1.54±0.51 versus 2.51±0.51 minutes; MD=−0.97 minutes, 95% CI: −1.21 to −0.73; p<0.001). Similarly, the time required to attain the T10 sensory level was significantly shorter in Group LD (5.51±0.95 versus 6.80±0.87 minutes; MD=−1.29 minutes, 95% CI: −1.72 to −0.85; p<0.001). A maximum sensory level of T6 was achieved less frequently in Group LD than Group LF (42.9% versus 68.6%; OR=0.34, 95% CI: 0.13–0.91; p=0.030), whereas T8 was more frequently the highest sensory level in Group LD (57.1% versus 31.4%; OR=2.91, 95% CI: 1.10–7.68; p=0.030). The mean time to reach the highest sensory level was significantly shorter in Group LD (11.17±1.40 versus 13.09±1.25 minutes; MD=−1.91 minutes, 95% CI: −2.55 to −1.28; p<0.001). In contrast, the time for two-segment sensory regression was significantly prolonged in Group LD (116.14±9.08 versus 72.86±3.89 minutes; MD=43.29 minutes, 95% CI: 39.95–46.62; p<0.001). The total duration of sensory blockade until regression to S1 was also substantially longer in Group LD (258.29±15.81 versus 169.71±6.41 minutes; MD=88.57 minutes, 95% CI: 82.82–94.33; p<0.001).

Table 3: Comparison of motor-block characteristics and postoperative analgesia between the LD and LF groups (N=70)

Table 3 shows significant differences in motor-block characteristics and postoperative analgesia between the groups. Motor block developed significantly faster in Group LD than Group LF (2.91±0.89 versus 4.11±0.68 minutes; MD=−1.20 minutes, 95% CI: −1.58 to −0.82; p<0.001). However, the time required to achieve maximum motor blockade was longer in Group LD (12.83±1.77 versus 10.91±0.82 minutes; MD=1.91 minutes, 95% CI: 1.26–2.57; p<0.001). The mean maximum Modified Bromage grade was significantly lower in Group LD than Group LF (2.43±0.50 versus 2.69±0.47; MD=−0.26, 95% CI: −0.49 to −0.02; p=0.030). Grade 3 motor block was less frequent in Group LD (42.9% versus 68.6%; OR=0.34, 95% CI: 0.13–0.91; p=0.030), whereas grade 2 motor block was more frequent (57.1% versus 31.4%; OR=2.91, 95% CI: 1.10–7.68; p=0.030). Despite producing a less intense maximum motor block, Group LD had a significantly longer duration of motor blockade (204.86±11.47 versus 132.57±5.99 minutes; MD=72.29 minutes, 95% CI: 67.92–76.65; p<0.001). The time to first rescue analgesic was also significantly prolonged in Group LD (236.57±16.17 versus 147.86±5.98 minutes; MD=88.71 minutes, 95% CI: 82.90–94.53; p<0.001). VAS scores were significantly lower in Group LD at three hours (0.23±0.55 versus 0.71±0.79; p=0.004) and four hours (2.97±0.66 versus 3.37±0.55; p=0.008). Although the VAS scores remained numerically lower at five and six hours, the differences were not statistically significant (p=0.051 and p=0.073, respectively).

Table 4: Comparison of perioperative haemodynamic parameters, sedation and adverse effects between the LD and LF groups (N=70)

Table 4 compares perioperative haemodynamic parameters, sedation and adverse effects. Baseline heart rate was comparable between Group LD and Group LF (75.20±5.14 versus 73.09±4.48 beats/min; p=0.071). At 50 minutes, however, the mean heart rate was significantly lower in Group LD (63.89±6.50 versus 69.20±4.71 beats/min; MD=−5.31, 95% CI: −8.02 to −2.61; p<0.001). Baseline systolic, diastolic and mean arterial pressures were comparable between the groups, with p-values of 0.273, 0.743 and 0.539, respectively. At 30 minutes, Group LD had significantly lower systolic blood pressure (110.06±5.14 versus 119.66±10.45 mmHg; MD=−9.60, 95% CI: −13.53 to −5.67; p<0.001), diastolic blood pressure (64.97±4.76 versus 68.86±7.72 mmHg; MD=−3.89, 95% CI: −6.95 to −0.83; p=0.014) and mean arterial pressure (80.00±4.55 versus 85.79±8.37 mmHg; MD=−5.79, 95% CI: −9.00 to −2.58; p=0.001). Respiratory rate and oxygen saturation at 30 minutes were identical between the groups, and no statistically significant differences were observed. Grade 2 sedation was significantly more frequent in Group LD than Group LF (28.6% versus 2.9%; OR=13.60, 95% CI: 1.63–113.25; p=0.003). Hypotension, bradycardia, nausea or vomiting, pruritus and shivering occurred infrequently, with no significant between-group differences. No patient in either group developed respiratory depression or post-dural puncture headache. The overall incidence of adverse effects excluding sedation was 20.0% in Group LD and 11.4% in Group LF, but the difference was not significant (OR=1.94, 95% CI: 0.51–7.33; p=0.325).

Table 1: Overall efficacy and safety The present study demonstrated that adding 5 µg dexmedetomidine to isobaric levobupivacaine produced a faster onset of sensory block and markedly prolonged sensory block, motor block and postoperative analgesia compared with 25 µg fentanyl. The duration of postoperative analgesia was approximately 89 minutes longer in Group LD, and the VAS score at four hours was significantly lower. These findings indicate that dexmedetomidine provided a stronger and more sustained potentiating effect on intrathecal levobupivacaine than fentanyl. These results agree with Attri et al. (2015)[1], who found that fentanyl improved the onset and duration of intrathecal levobupivacaine compared with levobupivacaine alone, confirming the benefit of an intrathecal adjuvant. However, comparative trials suggest that dexmedetomidine produces a more prolonged block than fentanyl. Sun et al. (2015)[2] and Li et al. (2015)[3] observed faster onset, prolonged sensory and motor blockade and improved postoperative analgesia with dexmedetomidine-containing spinal solutions. Jain et al. (2016)[4], in a study using hyperbaric levobupivacaine, similarly reported better prolongation of sensory and motor blockade with dexmedetomidine than fentanyl. The systematic review by Sun et al. (2017)[5] concluded that intrathecal dexmedetomidine prolonged the duration of sensory block, motor block and analgesia compared with fentanyl. The present findings are consistent with this pooled evidence, although the magnitude of benefit may vary according to the dose and baricity of the local anaesthetic, dexmedetomidine dose, surgical procedure and definition of block duration. The principal safety difference was the significantly greater incidence of grade 2 sedation in Group LD. Dexmedetomidine produces sedation through α₂-adrenoceptor activation in the locus coeruleus; therefore, mild and arousable sedation is an expected pharmacological effect. Importantly, the frequency of adverse effects other than sedation was not significantly different. This agrees with Rahimzadeh et al. (2018)[7], Khosravi et al. (2020)[9] and Kalbande et al. (2022)[13], who found that dexmedetomidine improved block duration without a major increase in clinically serious adverse events. Nevertheless, the wide confidence interval for sedation in the present study indicates imprecision due to the small number of events. Table 2: Sensory-block characteristics Dexmedetomidine produced a significantly faster onset of sensory block at both T12 and T10. The time to attain T12 was reduced by 0.97 minutes, while the time to T10 was reduced by 1.29 minutes. The time required to attain the highest sensory level was also shorter by approximately two minutes in Group LD. These findings support a synergistic interaction between dexmedetomidine and levobupivacaine. Presynaptic α₂-receptor activation inhibits the release of nociceptive neurotransmitters such as substance P and glutamate, while postsynaptic activation hyperpolarizes dorsal-horn neurons and enhances the local-anaesthetic block. Bhure and Jagtap (2019)[8], who directly compared dexmedetomidine and fentanyl with isobaric levobupivacaine, also reported favourable sensory-block characteristics with dexmedetomidine. Rastogi et al. (2020)[10] demonstrated similar prolongation of sensory blockade when dexmedetomidine was added to intrathecal levobupivacaine for caesarean delivery. More recently, Gupta et al. (2024)[14] compared the two adjuvants with 0.5% hyperbaric levobupivacaine and found that dexmedetomidine produced a faster onset and longer-lasting sensory blockade, supporting the direction of the present findings. The most pronounced difference involved sensory-block regression. Two-segment regression was prolonged by 43.29 minutes in Group LD, while total sensory-block duration until regression to S1 was prolonged by 88.57 minutes. Sun et al. (2017)[5], Paramasivan et al. (2020)[11] and Liu et al. (2020)[12] found that intrathecal dexmedetomidine significantly delayed sensory regression and prolonged the time to first analgesic request. The present results are therefore consistent with both individual randomized studies and pooled evidence. The distribution of the highest sensory level differed between the groups. T6 was attained more frequently in Group LF, whereas T8 was more frequent in Group LD. This does not indicate inferior efficacy of dexmedetomidine because both levels were sufficient for the included urological procedures, and Group LD had a faster onset and longer duration. The difference may be related to changes in solution density and spread caused by the adjuvants. Fentanyl-containing solutions may differ in baricity from dexmedetomidine-containing solutions, influencing cephalad distribution. Patient position, injection speed, spinal curvature and cerebrospinal-fluid volume may also contribute. Table 3: Motor block and postoperative analgesia The onset of motor block was 1.20 minutes faster with dexmedetomidine. Nevertheless, the time to maximum motor blockade was longer in Group LD, and a complete Modified Bromage grade 3 block occurred more frequently in Group LF. Thus, dexmedetomidine accelerated the initial development of motor block but did not produce a denser maximum block in a larger proportion of patients. Differences in intrathecal spread, local-anaesthetic baricity and the definition of motor-block onset may explain this apparently divergent finding. Despite the lower frequency of grade 3 block, motor recovery was markedly delayed in Group LD. Regression to Bromage grade 0 took 204.86 minutes with dexmedetomidine compared with 132.57 minutes with fentanyl, representing a mean prolongation of approximately 72 minutes. Sun et al. (2015)[2], Jain et al. (2016)[4], Rahimzadeh et al. (2018)[7] and Kalbande et al. (2022)[13] similarly reported prolongation of motor blockade with dexmedetomidine. This effect has been attributed to α₂-adrenoceptor activity on spinal motor neurons and enhancement of local-anaesthetic action. Although prolonged motor block can be beneficial during lengthy operations, it may delay ambulation and discharge after short procedures and should therefore be considered when selecting the adjuvant. The time to first rescue analgesic was prolonged by 88.71 minutes in Group LD. VAS scores were significantly lower at three and four hours, confirming superior early postoperative analgesia. At five and six hours, the differences were no longer significant, suggesting that the principal analgesic advantage was concentrated in the early postoperative period. Khosravi et al. (2020)[9] reported a significantly longer duration of analgesia with 5 µg dexmedetomidine than with 25 µg fentanyl. Paramasivan et al. (2020)[11] also concluded that intrathecal dexmedetomidine prolonged postoperative analgesia and reduced early postoperative pain scores. Liu et al. (2020)[12], specifically evaluating the 5-µg dexmedetomidine dose, found significant prolongation of sensory and motor blockade and analgesia. These observations support the dose selected in the present study. However, differences between studies in postoperative analgesic protocols, VAS assessment intervals and thresholds for rescue analgesia should be considered when comparing absolute durations. Table 4: Haemodynamic parameters, sedation and adverse effects Baseline haemodynamic parameters were comparable between the groups, supporting successful randomization. During the intraoperative period, Group LD showed significantly lower heart rate at 50 minutes and lower systolic, diastolic and mean arterial pressures at 30 minutes. This is pharmacologically expected because dexmedetomidine decreases central sympathetic outflow and norepinephrine release. Despite these reductions, clinically defined hypotension and bradycardia were not significantly more frequent in Group LD. Rahimzadeh et al. (2018)[7] and Khosravi et al. (2020)[9] also observed haemodynamic reductions with dexmedetomidine but did not demonstrate consistently significant differences in clinically important complications compared with fentanyl. In the Khosravi et al. trial, the incidences of hypotension, bradycardia and respiratory depression were comparable between the groups.[9] Kalbande et al. (2022)[13] similarly concluded that both adjuvants could be used effectively, provided that haemodynamic monitoring was maintained. In contrast, the meta-analysis by Liu et al. (2020)[12] found that 5 µg intrathecal dexmedetomidine increased the relative risk of transient bradycardia and hypotension. The present study showed the same direction of effect—hypotension occurred in 11.4% versus 5.7%, and bradycardia in 5.7% versus 2.9%—but the differences were not statistically significant. The absence of significance may reflect the limited sample size and low number of events rather than proof of equivalence. Hence, careful monitoring and immediate availability of intravenous fluids, vasopressors and atropine remain necessary. Grade 2 sedation was significantly more frequent with dexmedetomidine. Although this mild sedation may improve comfort during spinal anaesthesia, excessive sedation can interfere with neurological monitoring or delay recovery. Respiratory rate and oxygen saturation remained identical, and no respiratory depression occurred, indicating that the sedation was not accompanied by clinically measurable ventilatory compromise. This is an important advantage of dexmedetomidine over neuraxial opioids. The incidences of nausea or vomiting, pruritus, shivering and post-dural puncture headache were low and comparable. Pruritus occurred only in the fentanyl group, which is consistent with the opioid-mediated mechanism of neuraxial pruritus, although the single event precluded a meaningful statistical difference. Zhang et al. (2017)[6] reported that neuraxial dexmedetomidine reduced perioperative shivering, but the present study was underpowered to confirm such an effect.

Intrathecal dexmedetomidine 5 µg was more effective than fentanyl 25 µg as an adjuvant to 12.5 mg isobaric levobupivacaine for spinal anaesthesia in elective urological surgeries. Dexmedetomidine produced a significantly faster onset of sensory and motor blockade and prolonged two-segment sensory regression, total sensory blockade, motor blockade and postoperative analgesia. It also resulted in lower early postoperative pain scores and delayed the first requirement for rescue analgesia by approximately 89 minutes. Fentanyl produced a higher maximum sensory level and a denser maximum motor block more frequently. Dexmedetomidine was associated with greater reductions in heart rate and arterial blood pressure and a higher incidence of mild sedation. However, clinically significant hypotension, bradycardia, respiratory depression and other adverse effects were comparable between the groups. Thus, intrathecal dexmedetomidine may be preferred when prolonged spinal anaesthesia and postoperative analgesia are required, provided that haemodynamic parameters and sedation are carefully monitored.

Limitations of the Study

1. This was a single-centre study, which may limit the generalisability of its findings to other institutions and populations.
2. The sample size was relatively small, with 35 patients in each group. The study may therefore have been underpowered to detect uncommon adverse events.
3. Only ASA-PS grade I and II patients aged 20–70 years were included. The findings may not apply to high-risk, very elderly or severely comorbid patients.
4. Only a single dose of dexmedetomidine and fentanyl was evaluated; hence, the optimum dose–response relationship could not be determined.
5. A control group receiving isobaric levobupivacaine alone was not included, preventing estimation of the absolute benefit of each adjuvant.
6. Different types and durations of urological surgeries were included, introducing possible clinical heterogeneity.
7. Pain and sedation were assessed using clinical scoring systems, which are partly subjective.
8. Postoperative pain was primarily assessed for six hours, while follow-up for complications was limited to 24 hours. Delayed adverse events were not evaluated.
9. Total 24-hour analgesic consumption, time to ambulation, readiness for discharge and patient and surgeon satisfaction were not assessed.
10. The baricity of the final intrathecal drug mixtures was not measured, although differences in density could have influenced cephalad spread.
11. Haemodynamic measurements were mainly compared at individual time points instead of using a longitudinal repeated-measures model.
12. The study was not powered as an equivalence trial for safety; therefore, non-significant differences in adverse events do not establish equivalent safety.

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