European Journal of Cardiovascular Medicine

Spinal anaesthesia is a well-known and safe regional technique, especially for surgeries involving the lower limbs, perineum, and lower abdomen [1]. It provides intense sensory, motor, and sympathetic blockade with minimal doses of local anaesthetic compared to other regional techniques. Though the patient remains awake, this may cause variable levels of mental stress. Spinal anaesthesia offers several advantages such as low cost, minimal aspiration risk even in full-stomach patients, reduced blood loss, and good abdominal relaxation facilitating surgery; however, its main limitation is its relatively short duration, usually about 2–2.5 hours with hyperbaric bupivacaine [2]. To prolong the duration, various adjuvants like opioids, epinephrine, and neostigmine are used, each with distinct benefits and drawbacks. Central neuraxial blocks, particularly subarachnoid block (SAB) with hyperbaric bupivacaine, are widely preferred over epidural anaesthesia because of faster onset, denser block, and cost-effectiveness. Adjuvants such as opioids and α₂ agonists are commonly used intrathecally to enhance block efficacy and duration, while adequate sedation reduces anxiety and facilitates surgical performance [3,4]. Dexmedetomidine, a newer and highly selective α₂-adrenoreceptor agonist, provides sedation, analgesia, and sympatholysis without significant respiratory depression, maintaining hemodynamic stability. Approved by the FDA in 1999 for short-term ICU sedation (<24 hours), it acts primarily on α₂A receptors in the locus ceruleus, producing hypnotic and analgesic effects by suppressing noradrenergic neuronal firing and inhibiting norepinephrine release [5]. Dexmedetomidine has been shown to prolong sensory and motor blockade during SAB, producing satisfactory sedation with minimal side effects when given intravenously at a loading dose of 1 µg/kg over 10–20 minutes followed by maintenance of 0.4–0.5 µg/kg/hr. It has poor oral bioavailability due to first-pass metabolism, displays linear pharmacokinetics (0.2–0.7 µg/kg/hr), is 94% protein bound, and undergoes hepatic biotransformation with urinary excretion of inactive metabolites [6]. Because of its anxiolytic, analgesic, and sympatholytic properties, dexmedetomidine is increasingly used perioperatively for premedication, attenuation of stress response to laryngoscopy, and prevention of emergence delirium [7]. It enhances the effects of both intravenous and inhalational anaesthetics, reduces their required doses, lowers oxygen consumption, and may help prevent intraoperative myocardial ischemia. Hyperbaric bupivacaine, three to four times more potent than lignocaine, provides a long-lasting and dense block but limited postoperative analgesia, making prolonged pain relief an important clinical goal [8].

The aim of the present study is to assess the efficacy of intravenous dexmedetomidine on spinal anaesthesia. The objectives are to evaluate the onset and duration of sensory and motor blockade, observe the hemodynamic changes during the procedure, and assess the grade of sedation achieved with the use of dexmedetomidine as an adjunct to spinal anaesthesia.

Study Design and Setting

This prospective, randomized, double-blind, placebo-controlled study was conducted in the Department of Anaesthesia at Khaja Banda Nawaz Teaching and General Hospital, Kalaburagi, over a period of 18 months (1st December 2019 to 30th June 2021). Institutional ethical clearance and informed written consent were obtained from all participants. The total sample size was 150 patients.

Inclusion and Exclusion Criteria

Patients aged 18–55 years of either sex, belonging to ASA grade I or II, and scheduled for elective lower abdominal surgery under spinal anaesthesia with an expected duration of 90–120 minutes were included.

Exclusion criteria included patient refusal, pregnancy or lactation, patients on sedatives or CNS-acting drugs, those requiring intraoperative analgesic supplementation, contraindications to spinal anaesthesia, failed or inadequate blocks, allergy to study drugs, abnormal ECG, and patients on calcium-channel blockers, α-adrenergic blockers, or angiotensin receptor blockers.

Preoperative Evaluation

All patients underwent a thorough pre-anaesthetic evaluation including demographic details, clinical and personal history, systemic examination, and anthropometric measurements (height, weight, BMI). Baseline investigations included complete blood count, renal function tests, random blood sugar, urine analysis, ECG, and chest X-ray. Patients were advised nil per oral for at least six hours prior to surgery and preloaded with Ringer’s lactate (10–20 ml/kg) through an 18-gauge IV cannula.

Grouping and Drug Administration

Patients were randomly allocated using a computer-generated list into two groups of 75 each:

• Group D (Study group): Received IV dexmedetomidine 0.5 µg/kg diluted to 10 ml with normal saline, infused slowly over 10 minutes, followed by a maintenance infusion of 0.5 µg/kg/hr during surgery.
• Group C (Control group): Received an equivalent volume of normal saline administered in the same manner.

Anaesthetic Technique

In the operation theatre, standard monitors (ECG, NIBP, SpO₂) were connected, and baseline parameters were recorded. Under aseptic precautions, spinal anaesthesia was administered in the lateral decubitus position at the L3–L4 interspace using a 25-gauge Quincke needle. After confirming free flow of cerebrospinal fluid, 3 ml of 0.5% hyperbaric bupivacaine was injected intrathecally. The patient was then placed supine, and sensory block was assessed bilaterally by pinprick every minute until T6 level was achieved, after which surgery commenced. Inadequate or failed blocks were excluded.

Assessment of Sensory and Motor Block

Sensory block: Onset was defined as the time from intrathecal injection to loss of pinprick sensation at T10 dermatome. The highest sensory level, time to reach it, and time for two-segment regression were recorded.

Motor block: Evaluated using the Modified Bromage Scale (0–3). Onset was the time to reach Bromage 3, and duration was the time from injection to recovery to Bromage 0.

Hemodynamic Monitoring and Side Effects

Heart rate, systolic and diastolic blood pressure, and SpO₂ were recorded at baseline, every 2 minutes for the first 10 minutes, and every 5 minutes thereafter until the end of surgery. Hypotension (fall > 20% from baseline) was treated with IV ephedrine (6 mg), and bradycardia (HR < 50/min) with IV atropine (0.6 mg). Respiratory depression (RR < 8/min or SpO₂ < 94%) and other side effects such as nausea, vomiting, shivering, and dry mouth were recorded and managed appropriately.

Sedation Assessment

Sedation was evaluated using the Ramsay Sedation Score at baseline, 5 minutes after premedication, and at 30, 60, 90, 120, and 180 minutes intraoperatively. Scores ranged from 1 (anxious and agitated) to 6 (no response).

Postoperative Monitoring and Analgesia

Postoperative monitoring included HR, BP, SpO₂, and respiratory rate every 15 minutes for the first hour, every 30 minutes for 3 hours, and hourly up to 24 hours. Pain was assessed using the Visual Analogue Scale (VAS, 0–10). Rescue analgesia with IV tramadol 100 mg was given when VAS > 4, and the time of first analgesic request marked the end of spinal analgesia duration. Patients were also observed for 6 hours for complications such as nausea, vomiting, shivering, or headache.

Statistical Analysis

All data were analyzed using IBM SPSS v20 software. Quantitative variables were expressed as mean ± SD and compared using the unpaired Student’s t-test. A p-value < 0.05 was considered statistically significant.

Table 1: Age and Sex Distribution of Patients in Both Groups

This table 1 shows the distribution of patients based on age and sex in the two study groups Bupivacaine with Intravenous Dexmedetomidine and Bupivacaine with Normal Saline. Most patients in both groups belonged to the 31–40 years age range, indicating that the majority of participants were young to middle-aged adults. Male patients were predominant in both groups, reflecting a similar demographic pattern across the study population. The age and sex distribution between the two groups was comparable, suggesting appropriate randomization and uniformity of baseline characteristics.

Table 2: Height Distribution of Patients in Both Groups

This table 2 presents the height distribution of patients in the Bupivacaine with Intravenous Dexmedetomidine (Group D) and Bupivacaine with Normal Saline (Group C) groups. Most participants in both groups had a height between 176–185 cm, followed by those in the 166–175 cm range, indicating a predominance of individuals of average to tall stature. The overall height distribution was comparable between the two groups, demonstrating that both were well matched in terms of physical build, minimizing anthropometric bias in the study results.

Table 3: Distribution of Type of Surgery in Both Groups

This table 3 shows the distribution of different surgical procedures performed under spinal anaesthesia in the Bupivacaine with Intravenous Dexmedetomidine (Group D) and Bupivacaine with Normal Saline (Group C) groups. The majority of patients in both groups underwent appendicectomy, followed by anal surgeries and inguinal hernia repairs. A smaller number of patients underwent hysterectomy and femoral hernia repair. The pattern of surgical distribution was similar between the two groups, indicating that the type of surgery was evenly matched and unlikely to influence the comparative outcomes of spinal anaesthesia efficacy.

Table 4: Comparison of Sensory & motor block time and duration of block.

Mann Whitney test, P<0.05 = significant, ns= not significant

There was statistically significant (P<0.05) difference in sensory block time and duration of sensory block, during surgery and postoperative period in between two groups and there was no statistically significant (p>0.05) difference in motor block time and duration in between two groups (Table 4).

Figure 1: Maximum Sensory Level Achieved in Both Groups

This Figure 1 compares the maximum sensory level achieved following spinal anaesthesia in the Bupivacaine with Intravenous Dexmedetomidine (Group D) and Bupivacaine with Normal Saline (Group C) groups. The majority of patients in both groups attained a sensory block level up to T6, which was most common in Group D (88%) and slightly lower in Group C (82.6%). A few patients in both groups achieved levels at T5 and T7, with no patients attaining levels beyond these dermatomes. Overall, both groups achieved comparable sensory block heights, indicating similar spread of local anaesthetic within the subarachnoid space.

Table 5: Comparison of Peak Sensory Level Between the Two Groups

This table 5 compares the distribution of peak sensory block levels achieved in the Bupivacaine with Intravenous Dexmedetomidine (Group D) and Bupivacaine with Normal Saline (Group C) groups. The majority of patients in both groups attained a T6 sensory level, followed by a smaller proportion achieving T5 and T7 levels. Although a slightly higher number of patients in Group D reached a T5 level compared to Group C, the difference was statistically not significant (p = 0.2213), indicating that the addition of intravenous dexmedetomidine did not significantly alter the maximum sensory level attained.

Table 6: Comparison of Pulse Rate, Systolic and Diastolic Blood Pressure, and SpO₂ Between the Two Groups

This table 6 compares the intraoperative vital parameters pulse rate, systolic blood pressure (SBP), diastolic blood pressure (DBP), and oxygen saturation (SpO₂) between the Bupivacaine with Intravenous Dexmedetomidine (Group D) and Bupivacaine with Normal Saline (Group C) groups. All patients in both groups maintained stable hemodynamic parameters throughout the study period. Pulse rate, systolic and diastolic blood pressures remained within normal physiological limits, and oxygen saturation (SpO₂) was consistently above 94% in all cases. There were no episodes of bradycardia, hypotension, or desaturation in either group, indicating that intravenous dexmedetomidine maintained hemodynamic stability comparable to the control group.

Figure 2: Total Dose of Analgesia Received Within 72 Hours in Both Groups

This figure 2 compares the total dose of rescue analgesic administered during the first 72 hours postoperatively in the Bupivacaine with Intravenous Dexmedetomidine (Group D) and Bupivacaine with Normal Saline (Group C) groups. In Group D, 200 mg of analgesic was required in 29.3% of patients and 150 mg in 48%, whereas in Group C, 100 mg was needed in 50.6% and 200 mg in 49.3% of patients. The findings indicate that patients who received intravenous dexmedetomidine required a higher cumulative analgesic dose, though the distribution pattern suggests variability in individual analgesic needs between the groups.

Figure 3: Distribution of Side Effects in Both Groups

This figure 3 presents the incidence of intraoperative and postoperative side effects observed in the Bupivacaine with Intravenous Dexmedetomidine (Group D) and Bupivacaine with Normal Saline (Group C) groups. The most common side effects noted were bradycardia and hypotension in both groups, with slightly higher incidence of bradycardia in Group D (29.3%) and hypotension in Group C (29.3%). Sedation was observed only in Group D, consistent with the pharmacological action of dexmedetomidine, whereas nausea and vomiting were more frequent in Group C (16% and 13.3%, respectively). No severe adverse effects or respiratory complications were reported. Overall, dexmedetomidine use was associated with better sedation and fewer gastrointestinal side effects, while maintaining stable hemodynamics.

Table 7 : Comparison of  incidence of side effects between two groups.

Fisher's exact test, P<0.05,** = significant, ns= not significant, IQR = interquartile range, n=Number of patients

This table 7 compares the frequency of various side effects observed in the Bupivacaine with Intravenous Dexmedetomidine (Group D) and Bupivacaine with Normal Saline (Group C) groups. The results show that bradycardia, hypotension, and sedation were significantly more frequent in Group D, with p-values of 0.0273, 0.0399, and 0.0135, respectively. In contrast, a higher proportion of patients in Group C experienced no side effects, which was statistically significant (p = 0.0003). The incidence of nausea and vomiting did not differ significantly between the groups (p > 0.05). Overall, while dexmedetomidine use was associated with mild hemodynamic effects such as bradycardia and hypotension, it also provided the beneficial effect of sedation without increasing nausea or vomiting, suggesting a favorable safety profile when used judiciously.

Subarachnoid block (SAB) using 0.5% hyperbaric bupivacaine remains one of the most widely used regional anaesthetic techniques for abdominal and lower limb surgeries lasting about 2–2.5 hours [9, 10]. Several adjuvants, including opioids and α₂-agonists, have been evaluated to prolong the duration of SAB [11]. Although opioids effectively enhance analgesia, they are associated with pruritus and respiratory depression [12]. α₂-adrenergic agonists such as clonidine (α₂R:α₁R ratio 200:1) and dexmedetomidine are increasingly preferred for their sedative, analgesic, and sympatholytic effects [13]. Dexmedetomidine, a highly selective α₂-agonist, has been shown to extend the duration of both sensory and motor blockade in neuraxial [14] and peripheral nerve blocks [15] through supraspinal mechanisms that enhance anaesthetic and analgesic effects [16]. Its use in a single intravenous dose or continuous infusion has proven beneficial for maintaining anaesthesia and postoperative analgesia.

In our study, demographic characteristics such as age, height, and weight were comparable between groups, with mean age 34.23 ± 8.481 years in Group D and 33.51 ± 8.375 years in Group C. The mean weight and height were also similar across both groups, findings consistent with those of Ezhil Bharathi et al [17] and Siddesh et al [18], confirming adequate randomization and comparability of baseline characteristics.

Regarding sensory blockade, the mean onset time was 5.547 ± 1.855 minutes in Group D and 3.027 ± 1.15 minutes in Group C, showing a statistically significant difference (p < 0.05). The maximum sensory level achieved was at T6 in 88% of Group D and 82.6% of Group C, indicating no significant difference in peak sensory level (p > 0.05). These findings are similar to those reported by Ezhil et al [17], where dexmedetomidine shortened the onset of sensory blockade without affecting its maximum level. Ahmed et al [19] also demonstrated that intravenous dexmedetomidine accelerates sensory onset and prolongs duration when used as an adjunct to bupivacaine.

The duration of sensory blockade in our study was significantly longer in Group D (5–6 hours in 41.5% of cases) compared to Group C (40%), consistent with findings by Fazil et al [20], who reported extended sensory block duration and prolonged postoperative analgesia with intravenous dexmedetomidine.

The mean onset of motor block was 5.253 ± 1.306 minutes in Group D and 5.107 ± 0.9805 minutes in Group C, showing no significant difference (p > 0.05). The mean duration of motor block was 4.893 ± 0.9238 hours in Group D and 5.014 ± 1.104 hours in Group C (p > 0.05), indicating no statistically significant difference between groups.

The requirement of rescue analgesia was lower and delayed in Group D compared to Group C (p < 0.05), showing a clear analgesic benefit of dexmedetomidine. Hemodynamic parameters showed mild reductions in pulse rate and blood pressure in Group D intraoperatively but remained within physiological limits. Significant bradycardia was observed between 10 and 55 minutes intraoperatively, while systolic and diastolic pressures were lower in Group D but without adverse outcomes. Sedation scores were significantly higher in Group D during surgery and up to 12 hours postoperatively (p < 0.05), reflecting the sedative property of dexmedetomidine. None of the patients had a Ramsay score above 4, indicating that sedation was adequate but not excessive. In terms of adverse effects, bradycardia (29.3%) and sedation were more common in Group D, while hypotension, nausea, and vomiting were more frequent in Group C.

Visual Analogue Score (VAS) analysis revealed significantly lower pain scores in Group D between 4 and 9 hours postoperatively (p < 0.05), indicating superior postoperative analgesia, consistent with Priyanka et al [115] and Siddesh et al [112].

Overall, the present study demonstrates that intravenous dexmedetomidine, when administered as a loading dose followed by maintenance infusion during spinal anaesthesia, significantly prolongs the duration of sensory blockade, provides effective sedation, reduces postoperative pain, and minimizes analgesic requirement, while maintaining stable hemodynamics and minimal side effects.

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