Present randomised double-blinded prospective clinical study was conducted in the Department of Anaesthesia, Shrimati Bhikhiben Kanjibhai Shah Medical Institute and Research Centre (SBKS MIRC), Piparia, Vadodara, Gujarat, India. After obtaining approval from the Institutional Ethical Committee (SVIEC/UN/MEDI/BNPG23/AUG/24/72), the study was carried out over a period of 18 months (from March 2023 to September 2024) on patients undergoing elective infraumbilical surgeries (open abdominal hysterectomy and bilateral open inguinal hernia repair) under spinal anaesthesia. Written informed consent was obtained from all participants. This study conformed to Institutional Ethics Committee standards and the Helsinki Declaration. No names or initials were used in the study. The Consolidated Standards of Reporting Trials (CONSORT) statement [Table/Fig-1] was followed to conduct this single-centre, double-blinded Randomised Controlled Trial (RCT) with two parallel groups.

[Table/Fig-1]:

CONSORT flow diagram.

Inclusion criteria: Patients aged 18-60 years, belonging to the American Society of Anaesthesiologists (ASA) classification Grade I and II (well-controlled systemic diseases), who underwent elective open abdominal hysterectomies and bilateral open inguinal hernia repair under spinal anaesthesia were included in the study.

Exclusion criteria: Patients who were not willing to participate, had arrhythmias or heart block, were on beta blockers, had coagulation disorders or were on anticoagulant therapy, had infections or deformities or scars at the proposed puncture site, had allergies to the study drug, were classified as ASA Grade III (uncontrolled systemic disease of the heart, liver, kidney, hypertension, or diabetes) or IV, were underweight or obese {Body Mass Index (BMI) <18.5 kg/m² or ≥30 kg/m²}, or underwent surgeries with prolonged duration (≥3 hours) or involving excessive tissue manipulation or major blood loss were excluded from the study.

Sample size calculation: The sample size was calculated using Process Automation Software System (PASS) 15 (NVSS: National Vital Statistics System). A pilot study was performed with 15 patients in each group, which detected a predicted difference of 35% for the duration of postoperative analgesia between the two groups, with a type I error (α) of 0.05 and a power of 0.8 for the study. The calculated sample size was 75. To minimise the effect of data loss, 40 patients were recruited in each group.

In this parallel group design study, patients who met the inclusion criteria were divided into two groups of 40 patients each, based on a randomised computer-generated sequence. Both the assessor and the patients were blinded to the group allocation, using opaque sealed envelope methods.

Group-R1 received Inj. Ropivacaine 0.2% (3 mg/kg)+Inj. Dexamethasone (0.1 mg/kg) [7], while Group-R2 received Inj. Ropivacaine 0.2% (3 mg/kg)+Inj. Dexmedetomidine (1 μg/kg) [7] in bilateral landmark-guided TAP block. The total volume of the study drug in both groups was made up to 50 mL after adding normal saline, with 25 mL given on each side. As per the envelope, the study drug was prepared and administered to the assigned group by an anaesthesiologist not included in the study.

Preanaesthetic evaluation was conducted one day prior to the surgery and patients were educated on the assessment of postoperative evaluation using the Visual Analogue Scale (VAS) [17]. They were instructed not to take solid food six hours prior and clear fluids two hours prior to surgery. After thoroughly explaining the procedure, informed consent was documented.

Intravenous fluid was administered through an 18-gauge intravenous cannula before the surgery. Intravenous Inj. Glycopyrrolate 0.004 mg/kg and Inj. Ondansetron 0.1 mg/kg were given as premedication.

Surgery commenced after administering spinal anaesthesia using Inj. Hyperbaric Bupivacaine 0.5% (4 mL) and achieving a sensory level of T7. After the surgery was completed, bilateral TAP block was administered using the landmark technique, wherein a 23-gauge 1.5-inch blunt-tipped needle was placed in the triangle of Petit at the mid-axillary line, immediately above the iliac crest. A total of 25 mL of the study drug was given on each side after two pop sounds were heard (one pop sound when the needle passed through the external oblique muscle and another when the internal oblique muscle was crossed) following negative aspiration.

Postoperative pain was assessed using the VAS every 30 minutes for the first two hours and then hourly until the VAS reached ≥4, as evaluated by an independent, blinded observer. The time from TAP block administration (taken as zero) to the first administration of rescue analgesia (Inj. Diclofenac 75 mg) at VAS ≥4 was documented as the duration of analgesia [7]. Haemodynamic parameters, including Systolic Blood Pressure (SBP), Diastolic Blood Pressure (DBP), Heart Rate (HR) and Saturation (SpO₂), were monitored at the same intervals. Any adverse effects were recorded.

The data obtained from the case reports of each of the study participants were decoded and analysed after the end of the study.

The sample size of 80 patients, with 40 patients in each group, was determined using MedCalc 12.5 software. The collected data were tabulated for assessment. Numerical/continuous variables were presented as mean and Standard Deviations (SD), while categorical variables were presented as frequencies and percentages. Tests such as the unpaired Student’s t-test and/or Analysis of Variance (ANOVA) were used for numerical variables whenever appropriate for intergroup comparisons, while the Chi-square test was used for categorical variables. A p-value <0.05 was considered statistically significant, while a p-value <0.001 was regarded as highly significant.

All selected patients were able to complete the study without any dropouts. Both groups were comparable in terms of age, weight, gender, ASA classification, type of surgery and total duration of surgery (p-value >0.05) [Table/Fig-2]. The time duration to first rescue analgesia was significantly longer in Group-R2 compared to Group-R1 (308.18±12.3 vs. 239.78±14.23 minutes, p<0.0001) [Table/Fig-3].

The postoperative pain intensity assessed by VAS scores was significantly lower in Group-R2 compared to Group-R1 at all time points from 30 minutes to six hours post-block (p<0.0001) [Table/Fig-4]. The median (interquartile range) VAS scores were consistently lower in the dexmedetomidine group, suggesting a better quality of analgesia [Table/Fig-5].

There were no statistically significant differences in the haemodynamic parameters {heart rate, systolic blood pressure, diastolic blood pressure, Mean Arterial Pressure (MAP) and SpO₂} between the two groups (p>0.05) [Table/Fig-6]. Additionally, there were no significant incidences of side effects such as bradycardia, hypotension, nausea, vomiting, respiratory depression, dry mouth, or excessive sedation in either group during the study period.

In the present prospective randomised clinical study, dexmedetomidine provided a longer duration and better quality of postoperative analgesia compared to dexamethasone as an adjuvant to ropivacaine in TAP block for infraumbilical surgeries, with comparable haemodynamic parameters and incidences of adverse effects, thus accepting the hypothesis.

Postoperative pain management is a crucial component of perioperative care, as inadequate pain control can lead to delayed recovery, prolonged hospital stays and an increased risk of chronic pain [1,2]. The TAP block has emerged as an effective regional analgesic method for abdominal surgeries, providing effective analgesia to the skin, muscles and parietal peritoneum of the anterior abdominal wall by blocking the sensory nerves in the TAP [3]. However, the duration of analgesia with local anaesthetics alone may be limited, prompting the use of adjuvants to prolong the block duration, improve the quality of analgesia and decrease local anaesthetic toxicity [8,13].

The present study compared the efficacy of dexmedetomidine and dexamethasone as adjuvants to ropivacaine in TAP block for infraumbilical surgeries for postoperative analgesia. The baseline demographic profiles of patients in both study groups were comparable. The duration of postoperative analgesia, defined as the time from TAP block administration (taken as zero) to the first rescue analgesia (Inj. Diclofenac 75 mg) administration at VAS ≥4, was 22.19% longer in the dexmedetomidine group than in the dexamethasone group. Additionally, it provided better quality of analgesia, evidenced by significantly lower VAS scores at all time intervals post study drug administration until rescue analgesia was demanded.

Through an extensive literature search, it was observed that various authors investigated the effectiveness of TAP block in different surgeries using different local anaesthetics with varying doses of dexmedetomidine and/or dexamethasone as adjuvants. [Table/Fig-7] describes those studies and their findings [1,6,9,11,15,16,18-22].

The findings of the current study were consistent with those of various authors [7,9,11,15,18,19], who concluded that dexmedetomidine has higher efficacy, providing a significantly longer duration of analgesia and lower VAS scores at the time of the first analgesic request compared to dexamethasone at different doses as an adjuvant to local anaesthetic agents in TAP block.

The present study demonstrated that a lower dose of dexmedetomidine at 1 μg/kg was effective with minimal side effects. Zeng Y et al., compared different doses of dexmedetomidine (0.5, 1 and 2 μg/kg) in TAP block and found that while the duration of analgesia was significantly prolonged at the 2 μg/kg dose, it was also associated with excessive sedation [11].

Xue Y et al., compared dexmedetomidine as an adjuvant to 0.375% ropivacaine versus plain 0.375% ropivacaine in TAP block against intravenous analgesics and found that pain control was significantly more effective in the TAP block with dexmedetomidine [9]. This suggests that the TAP block can significantly improve pain management in the postoperative period compared to intravenous analgesics. As an adjuvant to local anaesthetics, dexmedetomidine has proven to be more effective than dexamethasone in other peripheral nerve blocks (e.g., brachial plexus block, caudal block) as well [23-25].

In contrast to the findings of the current and previously mentioned studies [7,9,11,15,18,19], where dexmedetomidine was found to be more effective, Partani S et al., found equal efficacy of dexmedetomidine and dexamethasone as adjuvants to levobupivacaine in TAP block for unilateral inguinal herniorrhaphy [20]. Maagaard M et al., conducted a meta-analysis and trial sequential analysis on the effects of combined dexamethasone and dexmedetomidine as adjuncts to peripheral nerve blocks. They found that the combination increased the duration of analgesia compared to placebo and dexmedetomidine alone [26]. Furthermore, this combination provided a similar duration of analgesia to that of dexamethasone and concluded that it is reasonable to use dexamethasone as the sole adjunct if the goal is to increase the duration of analgesia.

Postoperative haemodynamic parameters such as heart rate, SBP, DBP and respiratory rate were comparable between the groups in present study. Similar findings were observed by Garg K et al., in their study, which indicated no significant difference in the postoperative haemodynamic parameters between both groups [15]. However, in contrast, Singla N et al., reported that 10% of patients in the dexmedetomidine group experienced hypotension and bradycardia, while the dexamethasone group maintained stable haemodynamics [7]. This may be due to a decrease in the release of noradrenaline from the sympathetic nervous system, which might have exacerbated the decrease in systemic vascular resistance observed in their pregnant study patients.

In the current study, none of the patients experienced nausea, vomiting, respiratory depression, or sedation. Similar results were noted by Kartalov A et al., and Abdel-Wahab AH et al., where no major postoperative side effects were reported between both study groups [21,22].

Although various studies have suggested the efficacy of either dexamethasone or dexmedetomidine, this study demonstrated the dose-specific superiority of dexmedetomidine over dexamethasone [7,9,11,15,16,18-21]. This knowledge can help in modifying TAP block techniques for managing postoperative analgesia in infraumbilical surgery and can positively impact total systemic opioid consumption, patient satisfaction and long-term outcomes such as chronic pain and quality of life.

The present study has several strengths, including its randomised design, the use of expert guidance for precise TAP block administration and the comprehensive assessment of postoperative pain and haemodynamic parameters.

At the same time, there are various factors that might have affected the outcome of the study. Since pain is a subjective experience, many elements of the biopsychosocial components can impact pain assessment. This can be influenced by a family or personal history of mental health disorders, pre-existing chronic pain conditions, substance abuse, or opioid dependence, which may lead to lower pain thresholds and desensitisation to previously used analgesics. The VAS scale, when used for assessing pain, requires patients to express abstract sensory experiences using a linear measure, which may vary according to their cognitive skills and understanding, potentially impacting the pain assessment. In addition to these factors, disparities in anaesthetic sensitivity due to different ethnic backgrounds can significantly affect the outcome of this study. Furthermore, the time point at which the TAP block begins to take effect and the time at which the sensory effects of spinal anaesthesia begin to wear off could not be differentiated, which may be important in assessing postoperative analgesia provided by the TAP block.

Despite the attempt to compare these promising adjuvants in TAP block for postoperative pain relief in infra-umbilical surgeries, present study has several limitations. Firstly, postoperative analgesia and side effects were monitored for only 24 hours after surgery and thus, the complete analgesic efficacy and any delayed side effects of these drugs during the 48-hour postoperative period could not be assessed. Secondly, pain scores were measured at rest and pain and analgesic requirements during mobilisation could not be monitored, which is important as early ambulation is crucial for these patients. Thirdly, total analgesic consumption in both groups during the postoperative period was not assessed, which could have strengthened the study results. Additionally, a comparison with a placebo group or intravenous control was not conducted, making it impossible to ascertain whether the effects of dexamethasone or dexmedetomidine were due to systemic absorption or through perineural action. Lastly, as this is a single-centre hospital-based study, it lacks generalisability. These limitations can be addressed in further studies.

For patients undergoing infra-umbilical surgeries, 0.2% ropivacaine with dexmedetomidine administered in the bilateral TAP block provided a longer duration and better quality of postoperative analgesia without significant side effects compared to dexamethasone as an adjuvant. Thus, it can be safely applied in patients undergoing such surgeries to improve postoperative pain relief and expedite the recovery process. Future research can assess the effectiveness of TAP block with these adjuvants administered preoperatively to evaluate their effect on intraoperative analgesia, as well as the effectiveness of these adjuvants on long-term outcomes such as chronic pain and quality of life.