Comparison of effectiveness and safety of spinal anaesthesia with 0.25% versus 0.5% hyperbaric bupivacaine for endoscopic urological procedures: A prospective randomised controlled trial

Abstract

Background and Aims:

Spinal anaesthesia is an effective alternative technique for short-duration endoscopic urological procedures. Conventional 0.5% hyperbaric bupivacaine may be associated with prolonged motor blockade and haemodynamic instability, potentially delaying ambulation and discharge. This study aimed to compare the efficacy and safety of 0.25% and 0.5% hyperbaric bupivacaine for spinal anaesthesia in ambulatory endoscopic urological procedures.

Methods:

In this prospective, randomised, double-blind controlled study, 60 patients with American Society of Anesthesiologists physical status I and II undergoing elective lower urological endoscopic procedures were allocated into two groups (n = 30 each). Group A received 5 mg of 0.25% hyperbaric bupivacaine (2 mL), and Group B received 10 mg of 0.5% hyperbaric bupivacaine (2 mL) intrathecally. The primary outcomes were onset and duration of sensory and motor block. Secondary outcomes included haemodynamic changes, postoperative pain assessed using the visual analogue scale (VAS), time to ambulation, and duration of stay in the post-anaesthesia care unit.

Results:

The onset of sensory block was faster and the duration of sensory and motor block was significantly longer in Group B (P < 0.001). The ambulation time and post-anaesthesia care unit stay were significantly prolonged in Group B (P < 0.001). Haemodynamic fluctuations were more frequent with 0.5% bupivacaine. Post-operative pain scores at 2 h were lower in Group B (P < 0.001).

Conclusion:

Low-dose 0.25% hyperbaric bupivacaine provides effective spinal anaesthesia with improved haemodynamic stability, earlier ambulation, and faster recovery compared to 0.5% hyperbaric bupivacaine, making it suitable for ambulatory endoscopic urological procedures.

INTRODUCTION

Day-care surgery has become common with increasing use of minimally invasive techniques. Most lower urological procedures are short endoscopic procedures suitable for same-day discharge. For ambulatory surgery, the spinal anaesthetic technique should ensure effective surgical anaesthesia while promoting early post-operative recovery and timely discharge.[1]

Patients undergoing urological procedures are often elderly with multiple comorbidities, making them more susceptible to haemodynamic instability and post-operative complications.[2,3] Selection of an appropriate spinal anaesthetic technique is essential to optimise recovery after ambulatory surgery.[4] Frailty is associated with higher post-operative complication rates.[5] In selected patients, neuraxial anaesthesia may offer advantages over general anaesthesia by avoiding airway manipulation and reducing certain post-operative complications.[6,7] Conventional spinal anaesthesia may cause hypotension and prolonged motor blockade, potentially delaying ambulation and discharge. A sensory level up to T10 is generally adequate for these procedures. Hyperbaric 0.5% bupivacaine is widely used but may prolong recovery in ambulatory surgery.

Low-dose spinal anaesthesia using diluted hyperbaric bupivacaine has been investigated as a strategy to achieve effective intra-operative anaesthesia while enhancing haemodynamic stability and facilitating faster recovery.[8] Hyperbaric bupivacaine was selected because it is widely used for spinal anaesthesia in endoscopic urological procedures owing to its predictable block characteristics and established safety profile. This study compared low-dose (5 mg 0.25%) and conventional-dose (10 mg 0.5%) hyperbaric bupivacaine for spinal anaesthesia in endoscopic urological procedures.

The primary objective of this study was to compare the onset and duration of spinal block produced by 0.25% and 0.5% hyperbaric bupivacaine in patients undergoing endoscopic lower urological surgery. Secondary objectives included evaluation of haemodynamic stability, adverse effects, post-operative pain scores, time to ambulation, and duration of stay in the post-anaesthesia care unit (PACU).

METHODS

This prospective randomised double-blind study was conducted in a tertiary care teaching hospital from May to August 2025 after institutional ethics approval (vide approval No. EC/BMHR/2024/123 dated 26 April 2024). The trial was prospectively registered with the Clinical Trials Registry–India (CTRI/2024/10/074906 registered on 08 October 2024), and written informed consent was obtained from all participants. The study was conducted as per the principles of the Declaration of Helsinki (2013) and Good Clinical Practice guidelines. The study is reported in accordance with the Consolidated Standards of Reporting Trials (CONSORT) 2010 guidelines.

Sample size calculation was based on the primary outcome variable, namely, the duration of sensory block. Estimates for the expected treatment effect were derived from previous randomised studies evaluating different intrathecal doses of hyperbaric bupivacaine in endoscopic urological procedures.[2] A clinically relevant difference of 50 min with an assumed pooled standard deviation of 60 min was considered. With a two-sided α error of 0.05 and a study power of 80% (β = 0.20), the required sample size was calculated to be 27 participants in each group using the independent Student’s t-test. To account for potential dropouts, 30 patients were enroled in each group, resulting in a total sample size of 60.

Patients aged 18–60 years with American Society of Anesthesiologists (ASA) physical status I or II and scheduled for elective lower urological endoscopic procedures of 60 min or less duration under spinal anaesthesia were included. Patients with a body mass index greater than 30 kg/m², obstructive sleep apnoea, anticipated difficult airway, neuromuscular or neuropsychiatric disorders, spinal deformity, previous spinal surgery, coagulopathy, local infection at the puncture site, contraindications to regional anaesthesia, or allergy to local anaesthetics were excluded.

Participants were randomly allocated to two groups based on a computer-generated randomisation sequence. Allocation concealment was maintained using sealed, opaque envelopes. An anaesthesiologist who was not involved in the conduct of the study prepared the study medications. The patient, the anaesthesiologist administering the spinal block, and the observer recording perioperative data were blinded to group allocation.

Standard fasting guidelines were followed. Upon arrival in the operating room, standard ASA monitoring (electrocardiography, non-invasive blood pressure, and pulse oximetry) was applied. Baseline heart rate and blood pressure were recorded in the supine position. An 18-gauge intravenous cannula was inserted, and Ringer’s lactate 15 mL/kg was administered. Intravenous ondansetron 0.1 mg/kg was given.

Under aseptic precautions, lumbar puncture was performed in the sitting position at L2–L3 interspace using a 25-gauge Quincke spinal needle after local infiltration with lignocaine. The L2–L3 interspace was selected to facilitate reliable cerebrospinal fluid flow and consistent intrathecal drug administration while remaining within the safe lumbar region below the termination of the spinal cord. Following confirmation of free cerebrospinal fluid flow, the study drug was injected intrathecally. Group A received 5 mg of 0.25% hyperbaric bupivacaine prepared by diluting commercially available 0.5% hyperbaric bupivacaine containing dextrose with sterile distilled water (1ml distilled water added to 1ml of 0.5% hyperbaric bupivacaine) to obtain a total volume of 2 mL. The diluted solution remained functionally hyperbaric relative to cerebrospinal fluid and was prepared aseptically immediately before administration. Group B received 10 mg of 0.5% hyperbaric bupivacaine in a total volume of 2 mL. The study doses were selected based on previous evidence supporting the use of low-dose intrathecal hyperbaric bupivacaine for short-duration endoscopic urological procedures. A standard 10 mg dose was used as the comparator, while a reduced 5 mg dose was evaluated to determine whether adequate surgical anaesthesia could be achieved with improved haemodynamic stability and faster post-operative recovery.[9,10] Patients were positioned supine, and supplemental oxygen at 5 L/min was administered via facemask. Supplemental oxygen was administered as a routine institutional safety measure during regional anaesthesia to maintain adequate oxygen saturation and provide an additional margin of safety during the intra-operative period. Surgery began after achieving a T10 sensory block.

The primary outcome was duration of sensory block, defined as the time from onset of sensory block at T10 to regression to the S2 dermatome. Secondary outcomes were onset time of sensory block, onset and duration of motor block, maximum sensory level attained, haemodynamic changes, incidence of adverse effects, post-operative pain scores, time to achieve unaided ambulation, and recovery room stay duration.

Sensory block was assessed using pinprick at 1-min intervals for 10 min and every 10 min thereafter. The time taken for regression of the sensory block by two dermatomes was recorded. Motor block was evaluated using the Modified Bromage Scale (0–4) at similar intervals. Duration of motor block was defined as time to recovery to a Modified Bromage score of 0.

Heart rate, blood pressure, and oxygen saturation were recorded every 2 minutes for 15 minutes and then every 5 minutes thereafter. Hypotension was defined as a decrease in systolic blood pressure greater than 20% from baseline. Management of hypotension consisted of intravenous fluid resuscitation and repeated 6 mg doses of mephentermine as indicated. Bradycardia was defined as heart rate <50 beats/min, managed with intravenous atropine at a dose of 0.01 mg/kg. Other adverse events were managed according to institutional protocols, and conversion to general anaesthesia was undertaken if necessary.

Post-operatively, sensory block and motor block were assessed every 15 min until complete regression. Pain was evaluated using a visual analogue scale (VAS) ranging from 0 to 10 at 0, 2, 4, 6, 8, 12, and 24 h. Rescue analgesia consisted of intravenous tramadol 100 mg with paracetamol 1 g. Adverse effects such as nausea, vomiting, shivering, and headache were recorded. Time to ambulation is defined as the interval from completion of surgery to the patient’s ability to walk unaided for at least 5 metres with stable vital signs and without external support. Patients were discharged from the PACU once they met the following criteria: stable vital signs, adequate pain control, oxygen saturation >94% on room air, full consciousness, and ability to perform basic movements independently.

Statistical analysis was performed using International Business Machines (IBM) Statistical Package for the Social Sciences (SPSS) Statistics for Windows, version 26.0 (IBM Corp., Armonk, NY, USA). The Shapiro–Wilk test was applied to determine whether continuous variables followed a normal distribution. Continuous variables were expressed as mean ± standard deviation and compared using the independent Student’s t-test. Categorical variables were analysed using the Chi-square test or Fisher’s exact test where appropriate. A two-sided P value less than 0.05 was considered statistically significant.

RESULTS

Sixty patients were assessed for eligibility and randomised into two equal groups (n = 30 each). All recruited patients completed the study and were included in the final analysis [Figure 1]. No patient in either group experienced inadequate spinal block, and none required conversion to general anaesthesia during the procedure. Baseline demographic characteristics were similar between the two groups [Table 1]. The mean age was 54.07 ± 5.63 years in Group A and 50.90 ± 7.59 years in Group B (P = 0.072). The mean height was 157.33 ± 2.35 cm in Group A and 158.87 ± 3.84 cm in Group B (P = 0.067). The mean weight was 59.57 ± 5.42 kg in Group A and 58.93 ± 6.22 kg in Group B (P = 0.676). The distribution of gender and ASA physical status was similar between the groups (P = 0.716). The total surgical duration was comparable between Group A and Group B (37.8 ± 4.2 vs 38.5 ± 4.1 min; P = 0.654), with all procedures completed within 30–45 min.

Figure 1.

Consolidated standards of reporting trials (CONSORT) flow diagram of patient recruitment, randomisation, and analysis. Group A: 0.25% hyperbaric bupivacaine; Group B: 0.5% hyperbaric bupivacaine

Table 1.

Baseline demographic and clinical characteristics of the patients

Variable		Group A (0.25% Bupivacaine, n=30)		Group B (0.5% Bupivacaine, n=30)		P
Age (years)		54.07±5.63		50.90±7.59		0.072
Height (cm)		157.33±2.35		158.87±3.84		0.067
Weight (kg)		59.57±5.42		58.93±6.22		0.676
Gender (M/F)		18/12		16/14		0.602
ASA class I/II		16/14		15/15		0.795

Data are presented as mean±standard deviation (SD) or number of patients. ASA=American Society of Anesthesiologists Physical Status; M=Male; F=Female; n=Number of patients

The onset of sensory block was significantly faster in Group B (1.06 ± 0.13 min) compared with Group A (2.18 ± 0.19 min) (P < 0.001). The duration of sensory block was significantly longer in Group B (168.17 ± 6.09 min) than in Group A (105.83 ± 10.35 min) (P < 0.001). The mean difference in sensory block duration between Group A and Group B was 62.33 min [95% confidence interval (CI): (57.95–66.72)], indicating both statistical significance and high clinical relevance. The onset of motor block occurred earlier in Group B (1.48 ± 0.14 min) compared with Group A (4.92 ± 0.34 min) (P < 0.001). Similarly, the duration of motor block was significantly prolonged in Group B (134.33 ± 11.65 min) compared with Group A (66.00 ± 21.23 min) (P < 0.001) [Table 2]. The mean difference in motor block duration between Group A and Group B was 68.33 min (95% CI: 59.48–77.18), indicating both statistical significance and high clinical relevance.

Table 2.

Block characteristics (values expressed as mean±standard deviation)

Parameter		Group A (0.25%)		Group B (0.5%)		Mean Difference (95% CI)		P
Onset of sensory block (min)		2.18±0.19		1.06±0.13		-		<0.001
Duration of sensory block (min)		105.83±10.35		168.17±6.09		62.33 (57.95–66.72)		<0.001
Onset of motor block (min)		4.92±0.34		1.48±0.14		-		<0.001
Duration of motor block (min)		66.00±21.23		134.33±11.65		68.33 (59.48–77.18)		<0.001

Data are presented as mean±standard deviation (SD). CI=confidence interval. Mean difference is expressed as Group B − Group A

The post-operative VAS scores at 2 h were significantly lower in Group B (0.43 ± 0.50) compared with Group A (1.23 ± 0.43) (P < 0.001). Rescue analgesia during the first 6 post-operative hours was required in eight patients in Group A, compared with three in Group B. No patient required additional analgesia beyond the prescribed rescue regimen. The time to ambulation was significantly longer in Group B (4.83 ± 0.53 h) than in Group A (2.87 ± 0.35 h) (P < 0.001). The mean difference in time to ambulation between Group A and Group B was 1.97 h (95% CI: (1.74–2.20), Cohen’s d = 4.36), highlighting a clinically relevant delay in Group B. Duration of stay in the PACU was significantly prolonged in Group B (5.93 ± 0.49 h) compared with Group A (3.87 ± 0.35 h) (P < 0.001) [Table 3]. The mean difference in PACU stay between Group A and Group B was 2.07 h (95% CI: 1.85–2.28, Cohen’s d = 4.85), reflecting prolonged post-operative recovery in Group B. Prolonged PACU stay in Group B was mainly due to delayed motor recovery. Haemodynamic fluctuations were more frequent in Group B. Hypotension occurred in six patients in Group B compared with one patient in Group A. These episodes were managed with intravenous fluids and intermittent boluses of mephentermine. Bradycardia occurred in three patients in Group B, whereas no patient in Group A developed bradycardia. All episodes of bradycardia were treated successfully with intravenous atropine.

Table 3.

Post-operative recovery parameters (values expressed as mean±standard deviation)

Parameter		Group A (0.25%)		Group B (0.5%)		Mean Difference (95% CI)		P
VAS score at 2 h		1.23±0.43		0.43±0.50		-		<0.001
Time to ambulation (h)		2.87±0.35		4.83±0.53		1.97 (1.74–2.20)		<0.001
PACU discharge time (h)		3.87±0.35		5.93±0.49		2.07 (1.85 –2.28)		<0.001

VAS=Visual analogue scale; PACU=Post-anaesthesia care unit

DISCUSSION

This study demonstrates that 5 mg of 0.25% hyperbaric bupivacaine provides effective anaesthesia with greater haemodynamic stability and faster recovery than 10 mg of 0.5% bupivacaine. Although the higher dose resulted in a quicker onset and more prolonged sensory and motor blockade, these benefits were associated with delayed mobilisation, longer stay in the PACU, and a higher incidence of cardiovascular fluctuations.

The observed differences are likely attributable primarily to the reduced intrathecal dose (5 mg vs 10 mg) rather than concentration alone. The two groups were comparable in baseline characteristics, reducing potential confounding factors. The shorter onset time and denser block observed with the 10 mg dose reflect the recognised dose-dependent behaviour of intrathecal local anaesthetics. Chung et al.[11] reported that spinal block characteristics vary with the volume of hyperbaric bupivacaine. Patients receiving the higher dose achieved higher sensory levels, whereas the low-dose group typically attained T10, which was adequate for surgery. Similar findings have been reported by Ben-David et al.,[12] who demonstrated that reducing the milligram dose while maintaining intrathecal volume can preserve adequate anaesthesia while improving recovery characteristics.

The prolonged duration of sensory and motor block in the higher-dose group is consistent with earlier reports highlighting the relationship between intrathecal dose and block duration.[8,13] Kim et al.[9] found that low-dose dilute hyperbaric bupivacaine (4 mg) achieved satisfactory spinal anaesthesia for transurethral prostatectomy, with effective intra-operative conditions, minimal haemodynamic disturbances, and favourable post-operative recovery. In the present study, reducing the intrathecal bupivacaine dose to 5 mg was associated with earlier motor recovery, earlier ambulation, and improved haemodynamic stability compared with the conventional 10 mg dose. Using smaller intrathecal doses of local anaesthetics may maintain effective surgical anaesthesia while decreasing sympathetic blockade and supporting earlier post-operative recovery.[14]

Haemodynamic stability was better maintained in the 0.25% group in the present study. The characteristics of spinal blockade depend on several variables, including the administered dose and baricity of the local anaesthetic.[15] A higher intrathecal dose is likely to produce a more extensive sympathetic blockade due to greater cephalad spread, thereby increasing the risk of hypotension.[6,7] Previous studies have highlighted that low-dose spinal anaesthesia is associated with improved haemodynamic stability, faster post-operative recovery, and earlier mobilisation in ambulatory surgery.[16,17,18] Patra et al.[19] demonstrated that low-dose spinal anaesthesia using bupivacaine with intrathecal fentanyl provided satisfactory surgical anaesthesia for endoscopic urological procedures. However, the present trial specifically compared a reduced dose (5 mg, 0.25%) with the conventional dose (10 mg, 0.5%) of hyperbaric bupivacaine while maintaining an identical intrathecal volume. This design enabled evaluation of the independent effect of dose reduction on block characteristics, haemodynamic profile, post-operative recovery, and readiness for discharge by minimising the confounding effect of injectate volume and opioid supplementation. Our findings add clinically relevant evidence supporting the use of low-dose hyperbaric bupivacaine for ambulatory endoscopic urological procedures, where early recovery and same-day discharge are important objectives.

The present study involved preparation of a lower-concentration hyperbaric solution by dilution while keeping the intrathecal injectate volume constant. Therefore, maintaining the baricity of the diluted solution was an important methodological consideration. Hocking and Wildsmith emphasised that baricity is a major determinant of the distribution of intrathecal local anaesthetics.[20] In the present study, the diluted preparation remained a hyperbaric solution relative to cerebrospinal fluid at body temperature, which may have contributed to a more predictable spread of intrathecal anaesthesia.

Although post-operative pain scores at 2 h were lower in the higher-dose group, this modest analgesic advantage was offset by delayed mobilisation and prolonged PACU stay. In the current study, both the ambulation time and PACU discharge time were significantly shorter in the low-dose group, consistent with previously described dose-related recovery patterns.[1,4]

The study is strengthened by its randomised design and uniform anaesthetic protocol. An important novel aspect is the comparison of two intrathecal doses of hyperbaric bupivacaine administered in the same volume, enabling evaluation of the influence of dose on block characteristics, haemodynamic response, and post-operative recovery.

The present study has certain limitations, including a relatively small sample size and the inability to assess spontaneous voiding time due to routine post-operative catheterisation, off-label dilution of bupivacaine, non-inclusion of ASA class III–IV patients, and absence of subgroup analyses (e.g. elderly vs. younger patients), which may affect the external validity of the results. Larger multicentric studies are required to confirm these findings.

CONCLUSION

Low-dose 0.25% hyperbaric bupivacaine (5 mg) provides adequate spinal anaesthesia for short-duration endoscopic urological procedures with superior haemodynamic stability, earlier ambulation, and shorter PACU stay compared to 0.5% hyperbaric bupivacaine. Although the higher dose offers faster onset and prolonged analgesia, the low-dose regimen demonstrates a more favourable recovery profile and may be preferable in ambulatory settings.

Author contributions

AKV: Conceptualisation, study design, patient recruitment, supervision and critical revision of the manuscript. NM: Data collection, statistical analysis, interpretation of data, manuscript drafting and correspondence. AK: Patient management, data acquisition, literature review and manuscript revision. All authors reviewed and approved the final version of the manuscript and agree to be accountable for all aspects of the work.

Presentation at conferences/CMEs and abstract publication

None.

Study data availability

De-identified data may be requested with reasonable justification from the authors (email to the corresponding author) and shall be shared after approval as per the authors’ Institution policy.

Disclosure of use of artificial intelligence (AI)-assistive or generative tools

The AI tool was not used for study design, data collection, data analysis, interpretation of results or generation of scientific content. All scientific content was reviewed, verified and approved by the authors, who take full responsibility for the final manuscript.

Declaration of use of permitted tools

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Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.