European Journal of Cardiovascular Medicine

Transurethral resection of the prostate (TURP) is the gold standard surgical procedure for benign prostatic hyperplasia (BPH), routinely performed under spinal anaesthesia (SA) due to its advantages of rapid onset, superior intraoperative analgesia, and ability to monitor neurological status in awake patients.¹ Despite these benefits, spinal anaesthesia is associated with a high incidence of perioperative shivering, reported in 36–85% of patients.²

Shivering is an involuntary, repetitive, tremor-like muscular hyperactivity that arises primarily as a thermoregulatory response to hypothermia. Spinal anaesthesia impairs the normal thermoregulatory axis by inhibiting tonic vasoconstriction below the level of neural blockade through sympathetic and somatic neural blockade.2 The consequent redistribution of heat from the central core to the peripheral compartment leads to increased cutaneous heat loss, which exceeds metabolic heat production. Normothermic patients may also shiver due to central inhibition of thermoregulatory centers following neuraxial blockade.³

The clinical significance of shivering extends beyond patient discomfort. It is associated with a marked increase in oxygen consumption, up to 400% above basal metabolic rate, potentially precipitating hypoxemia, hypercarbia, and lactic acidosis.³ This is particularly hazardous in geriatric patients with limited cardiopulmonary reserve. Additional detrimental effects include elevated intraocular and intracranial pressures, increased surgical wound pain, impaired wound healing, and delayed discharge from the post-anaesthesia care unit (PACU).³

Patients undergoing TURP are at heightened risk of shivering due to absorption of large volumes of irrigating fluid administered at room temperature, causing rapid reduction in core body temperature.⁴ The consequent hypothermia produces haemodynamic responses and can significantly compromise surgical visualisation. Shivering may interfere with the surgeon's operative field, predisposing to injury of the urethra, bladder, or rectum, thereby prolonging operative time and increasing the risk of surgical complications.⁵

Geriatric patients, in whom TURP is predominantly performed, have a disproportionately higher risk of hypothermia-related morbidity and cardiac complications, making prevention of shivering imperative.⁵ Both pharmacological and non-pharmacological strategies have been employed to prevent shivering.⁶ Non-pharmacological methods include external warming with blankets, forced-air warming devices, and warmed intravenous fluids; however, these are cumbersome and only partially effective.⁶

Pharmacological prophylaxis includes agents such as pethidine, tramadol, ketamine, clonidine, dexmedetomidine, and ondansetron.⁷ Tramadol hydrochloride exerts its antishivering effect by inhibiting neuronal re-uptake of noradrenaline and 5-hydroxytryptamine (5-HT), facilitating 5-HT release, and activating μ-opioid receptors, thereby influencing central thermoregulatory control.⁸ Although effective, tramadol is associated with nausea, vomiting, and dizziness, which can add to patient discomfort.⁹

Ondansetron, a selective 5-HT³ receptor antagonist widely used for prevention of postoperative nausea and vomiting (PONV), has emerged as a promising anti-shivering agent. Its mechanism in shivering prevention is attributed to inhibition of 5-HT³ receptors in the central thermoregulatory pathways.⁸ Previous studies have reported favourable outcomes with ondansetron in reducing post-anaesthetic shivering.⁸

Despite individual evidence supporting both agents, a direct head-to-head comparison of intravenous tramadol and ondansetron specifically in TURP patients under spinal anaesthesia has not been reported. The present randomized controlled trial was therefore designed to compare the efficacy and safety of intravenous tramadol 0.5 mg/kg versus ondansetron 4 mg versus normal saline placebo in preventing post-spinal anaesthesia shivering in geriatric patients undergoing TURP.

Study Design and Ethical Approval This prospective, randomized, double-blind, placebo-controlled study was conducted in the Department of Anaesthesiology and Critical Care at Tertiary care Teaching Hospital over a period of 1 year, following approval from the Institutional Ethical Committee. Witnessed written informed consent was obtained from all participants prior to enrolment. Study Population All patients fulfilling the inclusion criteria and scheduled for elective TURP under spinal anaesthesia during the study period were eligible for enrolment. Inclusion Criteria Patients of American Society of Anesthesiologists Physical Status (ASA-PS) I and II, aged between 40 and 75 years, scheduled for elective TURP under spinal anaesthesia were included. Exclusion Criteria Patients were excluded if they had an initial body temperature >38°C or <36°C, received intraoperative blood transfusion, or had ASA physical status III or above. Sample Size and Randomization A total of 105 patients were randomized into three groups of 35 each using a computer-generated randomisation list. The study drugs were prepared and administered by a fellow anaesthesiologist not involved in data collection or analysis, ensuring allocation concealment. The primary investigator collecting intraoperative and postoperative data was blinded to group allocation. Group A (n=35): Received tramadol 0.5 mg/kg diluted in 10 mL normal saline IV over 5 minutes. Group B (n=35): Received ondansetron 4 mg diluted in 10 mL normal saline IV over 5 minutes. Group C (n=35): Received 10 mL plain normal saline IV over 5 minutes (control group). Anaesthetic Technique No premedication was administered. Upon arrival in the operating room, standard monitoring including pulse oximetry (SpO₂), electrocardiography (ECG), and non-invasive blood pressure (NIBP) were established. Baseline recordings of vital parameters and tympanic membrane temperature were documented. Intravenous access was secured and pre-loading with 10 mL/kg Ringer's lactate solution was administered. Patients were positioned in the sitting position for subarachnoid block under strict aseptic precautions. The L3–L4 or L4–L5 intervertebral space was identified; skin and subcutaneous tissue were infiltrated with 2 mL of 2% lignocaine. Spinal anaesthesia was administered using 2.6 mL of 0.5% hyperbaric bupivacaine via a 23-G Quincke's tip spinal needle. Patients were then repositioned supine and covered with a single cotton sheet. Sensory block was assessed using an ethyl alcohol spirit swab test and motor block was assessed using the Modified Bromage Scale, aiming for a sensory level of T10 or above. The study drug was administered at the time of surgical draping. Monitoring and Outcome Measures Heart rate, blood pressure, SpO₂, and core temperature were recorded every 5 minutes intraoperatively and every 10 minutes postoperatively for one hour. Shivering was assessed using the five-point Crossley and Mahajan scale: Grade 0 – no shivering; Grade 1 – piloerection, peripheral vasoconstriction or cyanosis without muscle activity; Grade 2 – visible muscle activity confined to one muscle group; Grade 3 – visible activity in more than one muscle group; Grade 4 – gross muscle activity involving the whole body. Grades 3 and 4 were defined as clinically significant shivering. Sedation was graded using the four-point Filos et al. scale: Grade 1 – awake and alert; Grade 2 – drowsy, responsive to verbal stimuli; Grade 3 – drowsy, arousable to physical stimuli; Grade 4 – unarousable. Management of Complications Bradycardia (pulse rate <50/minute) was treated with injection atropine 0.6 mg IV. Hypotension (blood pressure <90/60 mmHg) was managed with injection mephentermine 3 mg IV. Nausea and vomiting were treated with injection dexamethasone 8 mg IV. Statistical Analysis Data were analysed using SPSS version 25.0. Continuous variables were expressed as mean ± standard deviation and compared using one-way ANOVA followed by Tukey's post-hoc test. Categorical variables were analysed using the Chi-square test or Fisher's exact test. A p-value <0.05 was considered statistically significant. Study Design and Ethical Approval This prospective, randomized, double-blind, placebo-controlled study was conducted in the Department of Anaesthesiology and Critical Care at Tertiary care Teaching Hospital over a period of 1 year, following approval from the Institutional Ethical Committee. Witnessed written informed consent was obtained from all participants prior to enrolment. Study Population All patients fulfilling the inclusion criteria and scheduled for elective TURP under spinal anaesthesia during the study period were eligible for enrolment. Inclusion Criteria Patients of American Society of Anesthesiologists Physical Status (ASA-PS) I and II, aged between 40 and 75 years, scheduled for elective TURP under spinal anaesthesia were included. Exclusion Criteria Patients were excluded if they had an initial body temperature >38°C or <36°C, received intraoperative blood transfusion, or had ASA physical status III or above. Sample Size and Randomization A total of 105 patients were randomized into three groups of 35 each using a computer-generated randomisation list. The study drugs were prepared and administered by a fellow anaesthesiologist not involved in data collection or analysis, ensuring allocation concealment. The primary investigator collecting intraoperative and postoperative data was blinded to group allocation. Group A (n=35): Received tramadol 0.5 mg/kg diluted in 10 mL normal saline IV over 5 minutes. Group B (n=35): Received ondansetron 4 mg diluted in 10 mL normal saline IV over 5 minutes. Group C (n=35): Received 10 mL plain normal saline IV over 5 minutes (control group). Anaesthetic Technique No premedication was administered. Upon arrival in the operating room, standard monitoring including pulse oximetry (SpO₂), electrocardiography (ECG), and non-invasive blood pressure (NIBP) were established. Baseline recordings of vital parameters and tympanic membrane temperature were documented. Intravenous access was secured and pre-loading with 10 mL/kg Ringer's lactate solution was administered. Patients were positioned in the sitting position for subarachnoid block under strict aseptic precautions. The L3–L4 or L4–L5 intervertebral space was identified; skin and subcutaneous tissue were infiltrated with 2 mL of 2% lignocaine. Spinal anaesthesia was administered using 2.6 mL of 0.5% hyperbaric bupivacaine via a 23-G Quincke's tip spinal needle. Patients were then repositioned supine and covered with a single cotton sheet. Sensory block was assessed using an ethyl alcohol spirit swab test and motor block was assessed using the Modified Bromage Scale, aiming for a sensory level of T10 or above. The study drug was administered at the time of surgical draping. Monitoring and Outcome Measures Heart rate, blood pressure, SpO₂, and core temperature were recorded every 5 minutes intraoperatively and every 10 minutes postoperatively for one hour. Shivering was assessed using the five-point Crossley and Mahajan scale: Grade 0 – no shivering; Grade 1 – piloerection, peripheral vasoconstriction or cyanosis without muscle activity; Grade 2 – visible muscle activity confined to one muscle group; Grade 3 – visible activity in more than one muscle group; Grade 4 – gross muscle activity involving the whole body. Grades 3 and 4 were defined as clinically significant shivering. Sedation was graded using the four-point Filos et al. scale: Grade 1 – awake and alert; Grade 2 – drowsy, responsive to verbal stimuli; Grade 3 – drowsy, arousable to physical stimuli; Grade 4 – unarousable. Management of Complications Bradycardia (pulse rate <50/minute) was treated with injection atropine 0.6 mg IV. Hypotension (blood pressure <90/60 mmHg) was managed with injection mephentermine 3 mg IV. Nausea and vomiting were treated with injection dexamethasone 8 mg IV. Statistical Analysis Data were analysed using SPSS version 25.0. Continuous variables were expressed as mean ± standard deviation and compared using one-way ANOVA followed by Tukey's post-hoc test. Categorical variables were analysed using the Chi-square test or Fisher's exact test. A p-value <0.05 was considered statistically significant.

A total of 105 patients were enrolled and randomized, with 35 patients in each group. All patients completed the study without exclusion. The demographic profile, baseline vital parameters, and ASA status were comparable across the three groups (Table 1).

Table 1: Demographic Data and Baseline Parameters

Interpretation: All three groups were comparable in terms of age, weight, ASA status, baseline heart rate, blood pressure, and core temperature. No statistically significant differences were noted (p>0.05), confirming adequate randomization.

Table 2 illustrates the intraoperative core temperature changes. A progressive decline in temperature was observed in all groups following spinal anaesthesia, with the most pronounced fall in the control group.

Table 2: Intraoperative Core Temperature (°C) at Various Time Intervals

Interpretation: Core body temperature declined progressively in all groups following spinal anaesthesia and irrigation. The drop was significantly more pronounced in Group C (control) at 30, 45, and 60 minutes compared to Groups A and B (p<0.05). Groups A and B showed comparable temperature preservation.

Table 3 presents the incidence and severity of shivering across the three groups. Clinically significant shivering (Grade 3–4) was significantly lower in both treatment groups compared to controls.

Table 3: Incidence and Grade of Shivering

Interpretation: Clinically significant shivering (Grade 3+4) occurred in 8.57% (Group A), 14.28% (Group B), and 54.28% (Group C). Both tramadol and ondansetron significantly reduced the incidence of shivering compared to placebo (p<0.001). The difference between Group A and Group B was not statistically significant (p=0.48).

Table 4 summarizes intraoperative haemodynamic parameters. No clinically significant differences were observed in heart rate and blood pressure between the groups.

Table 4: Haemodynamic Parameters (Mean ± SD)

Interpretation: Haemodynamic parameters including heart rate, systolic blood pressure, and oxygen saturation were stable in all three groups throughout the study period. The incidence of intraoperative bradycardia and hypotension was comparable and clinically manageable across all groups (p>0.05).

Table 5 presents the sedation scores across groups. Mild sedation was observed in some patients in Group A, consistent with tramadol's opioid properties.

Table 5: Sedation Scores (Filos Scale)

Interpretation: Mild sedation (Grade 2) was significantly more common in Group A (tramadol) compared to Groups B and C (p=0.04), consistent with the central opioid action of tramadol. No patient in any group developed Grade 3 or 4 sedation, indicating an acceptable safety profile.

Table 6: Adverse Effects

Interpretation: Nausea (20%), vomiting (11.43%), and dizziness (14.29%) were significantly more frequent in Group A (tramadol) compared to Groups B and C (p<0.05). Ondansetron demonstrated a significantly superior adverse effect profile. Pruritus was observed exclusively in the tramadol group, though not statistically significant (p=0.12). No serious adverse events were reported in any group.

The present study evaluated and compared the efficacy of intravenous tramadol (0.5 mg/kg) and ondansetron (4 mg) versus normal saline placebo in preventing post-spinal anaesthesia shivering in geriatric patients undergoing TURP. Our results demonstrate that both tramadol and ondansetron significantly reduced the incidence of clinically significant shivering (Grade 3–4) compared to placebo (8.57% and 14.28% versus 54.28% respectively, p<0.001). The difference between the two treatment groups was not statistically significant (p=0.48), suggesting comparable overall efficacy, although tramadol showed marginally superior results.

The high incidence of shivering in our control group (54.28%) is consistent with previously published data. Wason et al.¹⁰ in their study reported shivering incidence of approximately 50–60% in TURP patients under spinal anaesthesia who did not receive prophylactic anti-shivering agents. The heightened susceptibility to shivering in TURP patients specifically relates to large-volume, room-temperature irrigation fluid absorption, which generates a significant thermogenic challenge not present in other procedures performed under spinal anaesthesia.⁴

Our finding that tramadol 0.5 mg/kg IV significantly reduced shivering incidence to 8.57% is consistent with several landmark studies. Mathews et al.¹¹ reported that tramadol 0.5 mg/kg IV significantly reduced shivering in patients undergoing lower limb surgeries under spinal anaesthesia compared to placebo. Similarly, Bhattacharya et al.¹² demonstrated an anti-shivering efficacy of tramadol comparable to pethidine, with fewer respiratory adverse effects. The mechanism by which tramadol prevents shivering is multifactorial: it activates μ-opioid receptors in the dorsal horn of the spinal cord and hypothalamic thermoregulatory centres, inhibits neuronal reuptake of serotonin and noradrenaline, and increases the shivering threshold.^8,12

The efficacy of ondansetron 4 mg IV in reducing shivering (14.28%) observed in the present study is in agreement with findings reported by Sajedi et al.¹³ who demonstrated that ondansetron significantly reduced both incidence and severity of post-spinal shivering in caesarean section patients. The thermoregulatory role of serotonin via 5-HT3 receptors, particularly in the hypothalamic preoptic area and anterior hypothalamus, provides the pharmacological basis for ondansetron's efficacy. Activation of 5-HT3 receptors is known to lower the shivering threshold, and their antagonism by ondansetron effectively raises this threshold, preventing the initiation of shivering response.^13,14

Shakya et al.¹⁵ conducted a randomized double-blind comparison of tramadol and ondansetron for prevention of spinal anaesthesia-induced shivering in patients undergoing orthopaedic procedures. Their results showed that tramadol reduced shivering in 85.7% of cases compared to ondansetron's 74.3%, a difference which, similar to ours, did not achieve statistical significance. However, nausea and vomiting were significantly more common with tramadol, corroborating our findings. Our study extends this observation specifically to the TURP patient population, where the additional thermal load from irrigation fluid makes anti-shivering prophylaxis particularly important.

Harkouk et al.¹⁶ published a systematic review demonstrating that serotonin antagonists, including ondansetron and granisetron, significantly reduced postoperative shivering with an acceptable safety profile. In contrast, tramadol, while highly effective, was associated with a three-fold higher incidence of nausea and a two-fold higher incidence of vomiting. Our results, showing nausea in 20% and vomiting in 11.43% of tramadol recipients compared to 5.71% and 2.86% in the ondansetron group, are consistent with this meta-analytic data.

Temperature trends in our study showed progressive core temperature decline in all groups, with a significantly more pronounced fall in the control group from 30 minutes onward. This confirms the thermal challenge inherent to TURP under spinal anaesthesia. The relatively preserved temperature in treatment groups may reflect additional thermostatic effects of both agents, consistent with findings by Kelsaka et al.¹⁷ who demonstrated that tramadol administration was associated with maintenance of core temperature compared to placebo.

Haemodynamic stability was well maintained in both treatment groups. No significant episodes of bradycardia or hypotension attributable to study drugs were observed. The safety of ondansetron in terms of haemodynamic preservation aligns with Abdallah et al.¹⁸ who reported no significant haemodynamic changes with prophylactic ondansetron 4 mg in spinal anaesthesia patients. This is particularly relevant in elderly TURP patients who are haemodynamically vulnerable.

The sedation profile in our study showed that mild sedation (Grade 2 Filos scale) was significantly more common in the tramadol group (22.86%) compared to ondansetron (8.57%) and control (5.71%) groups. While mild sedation may be tolerated in anaesthetised patients, in the TURP setting where spinal anaesthesia allows the patient to remain awake – an advantage for monitoring neurological status and detecting early signs of TURP syndrome – excessive sedation is undesirable. Ondansetron's lack of sedative effect is therefore a clinically important advantage. These observations concur with Deng et al.¹⁹ who highlighted sedation as a limiting adverse effect of tramadol compared to 5-HT3 antagonists.

Comparing with other pharmacological interventions, dexmedetomidine and ketamine have also been studied for anti-shivering prophylaxis. Bajwa et al.²⁰ demonstrated that dexmedetomidine 0.5 μg/kg significantly reduced shivering but was associated with bradycardia and hypotension, limiting its utility in elderly patients with cardiovascular co-morbidities. Ketamine, though effective, is associated with psychomimetic effects and haemodynamic stimulation. In contrast, both tramadol and ondansetron demonstrated favourable haemodynamic stability in our study, making them preferable agents in the geriatric TURP population.

Considering the balance of efficacy and adverse effects, ondansetron appears to offer a more favourable overall risk-benefit profile in TURP patients requiring awake monitoring under spinal anaesthesia, while tramadol remains an effective alternative with marginally superior anti-shivering efficacy but a higher burden of gastrointestinal side effects. The dual benefit of ondansetron – preventing both shivering and PONV – represents an additional clinical advantage in this patient population.²¹

Limitations of the present study include the relatively small sample size and single-centre design, which may limit generalisability. Future multi-centre trials with larger sample sizes and head-to-head comparisons incorporating dose-response evaluation and combination therapies would be valuable in establishing definitive guidelines for anti-shivering prophylaxis in TURP.

Both intravenous tramadol (0.5 mg/kg) and ondansetron (4 mg) are effective and safe pharmacological agents for prevention of post-spinal anaesthesia shivering in geriatric patients undergoing TURP. Tramadol demonstrated marginally superior anti-shivering efficacy, but ondansetron is associated with a significantly better adverse effect profile, particularly regarding nausea, vomiting, and sedation. Given the awake nature of spinal anaesthesia in TURP patients, ondansetron may be preferred as a first-line prophylactic agent. Either agent is superior to placebo and should be incorporated into the perioperative management of TURP patients to improve patient comfort, safety, and surgical conditions.

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