European Journal of Cardiovascular Medicine

Upper limb surgeries are commonly performed procedures that require effective perioperative pain management for optimal outcomes and patient satisfaction. Peripheral nerve blocks, particularly brachial plexus blocks, have become an integral component of multimodal analgesia for these procedures, offering superior pain control while minimizing the systemic side effects associated with general anesthesia and opioid analgesics. The supraclavicular approach to brachial plexus blockade has gained widespread acceptance due to its reliability, comprehensive sensory coverage, and relative technical ease when performed under ultrasound guidance. This approach targets the brachial plexus at the level of the trunks and divisions, where the neural elements are compactly arranged, facilitating complete upper extremity anesthesia with a single injection technique.[1]

The advent of ultrasound guidance has revolutionized regional anesthesia practice by allowing real-time visualization of neural structures, surrounding vasculature, pleura, and the advancing needle. This technological advancement has significantly enhanced the safety profile and success rate of supraclavicular blocks, greatly reducing the risk of pneumothorax and inadvertent vascular puncture which were previously concerning complications of landmark-based techniques. Kapral et al. demonstrated that ultrasound guidance for supraclavicular brachial plexus blocks increased success rates from 74% to 99% when compared to nerve stimulation techniques alone.[2] Additionally, ultrasound guidance has been shown to reduce the onset time of sensory and motor blockade, decrease the volume of local anesthetic required, and extend the duration of analgesia, making it the current gold standard for performing this block.[3]

The pursuit of extended post-operative analgesia without escalating local anesthetic doses and associated toxicity risks has led to the exploration of various adjuvants to enhance block efficacy and duration. Among these, alpha-2 adrenergic receptor agonists have demonstrated considerable promise. These agents act through a variety of mechanisms including vasoconstriction, direct inhibition of peripheral nerve action potentials, suppression of the release of pro-inflammatory mediators, and modulation of spinal and supraspinal pain pathways.[4] Two such agents that have garnered significant clinical interest are clonidine and dexmedetomidine, with the latter being a more selective alpha-2 adrenergic receptor agonist with an alpha-2 selectivity ratio of 1620:1 compared to 220:1 for clonidine.[5]This study aims to compare the efficacy and safety of clonidine versus dexmedetomidine as adjuvants to ropivacaine in ultrasound-guided supraclavicular brachial plexus blocks for patients undergoing upper limb surgeries.

This prospective, randomized, double-blind study was conducted at R.L. Jalappa Hospital and Research Centre, Tamaka, Kolar, from May 2023 to October 2024 after obtaining institutional ethics committee approval. A total of 106 ASA I-II patients, aged 18-60 years, scheduled for elective or emergency upper limb surgeries were enrolled. Sample size was calculated based on a previous study by Sangita Mandal et al.[6], with a minimum of 53 patients required per group to detect a clinically significant difference in the duration of analgesia. Patients were randomly allocated into two groups using computer-generated random numbers and sealed envelope technique. Group A (n=53) received 0.5% ropivacaine 30mL with clonidine 2μg/kg, while Group B (n=53) received 0.5% ropivacaine 30mL with dexmedetomidine 1μg/kg, both diluted with normal saline to a total volume of 32mL. Patients with known allergies to the study drugs, requiring surgeries in both upper limbs, or suffering from cardiovascular, neurological, renal, or coagulation disorders were excluded. In the operating theatre, standard monitoring was established, and baseline vital parameters were recorded. Patients were positioned supine with the head turned away from the side to be blocked. Using a high-frequency linear ultrasound probe (8-13 MHz) in the supraclavicular fossa, the brachial plexus was identified as hypoechoic structures lateral to the subclavian artery. Under ultrasound guidance with an in-plane approach, a 22G, 50mm needle was directed toward the brachial plexus, and after confirming negative aspiration, the prepared solution was injected. Sensory block was assessed using pinprick test in the distribution of median, ulnar, radial, and musculocutaneous nerves. Motor block was evaluated using the modified Bromage scale. Block onset, duration, hemodynamic parameters, sedation levels, and adverse effects were recorded. Rescue analgesia (intravenous diclofenac sodium 75mg) was administered when VAS score ≥4 or upon patient request. Data were analyzed using SPSS version 20.0, with p<0.05 considered statistically significant.

The demographic characteristics including age, gender, BMI, ASA physical status, and duration of surgery were comparable between the two groups, establishing a homogeneous study population (Table 1).

The primary outcomes of the study (Table 2) showed that the onset of sensory block was significantly faster in Group B (dexmedetomidine) compared to Group A (clonidine) (6.95±1.47 vs 9.28±1.80 minutes, p<0.001). Similarly, the onset of motor block was more rapid in Group B than in Group A (8.70±2.00 vs 12.08±2.40 minutes, p<0.001). The duration of sensory block was significantly longer in Group B compared to Group A (668.26±41.65 vs 551.81±43.93 minutes, p<0.001). The motor block duration was also extended in Group B compared to Group A (595.06±42.37 vs 497.94±46.61 minutes, p<0.001).

The postoperative analgesia parameters (Table 3) demonstrated that the time to first rescue analgesia was substantially prolonged in Group B compared to Group A (716.45±76.88 vs 579.15±57.30 minutes, p<0.001). The visual analog scale (VAS) pain score at the time of rescue analgesia was significantly lower in Group B compared to Group A (3.28±1.10 vs 4.51±1.09, p<0.001). Patients in Group B required fewer rescue analgesics in the first 24 hours compared to those in Group A (1.92±0.85 vs 3.51±1.15, p<0.001). The Ramsay sedation score was higher in Group B compared to Group A (2.55±0.64 vs 2.11±0.32, p<0.001), indicating a greater degree of sedation, though within clinically acceptable limits.

The hemodynamic parameters and adverse effects (Table 4) showed no significant differences between the groups. Heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure, and oxygen saturation remained stable throughout the observation period in both groups. The incidence of adverse effects was low, with bradycardia being the most common (11.3% in Group A vs 5.7% in Group B), followed by nausea/vomiting (7.5% in Group A vs 3.8% in Group B). Although there was a trend toward fewer adverse effects in Group B (90.6% of patients with no adverse effects) compared to Group A (81.1%), this difference was not statistically significant (p=0.156).

Table 1: Demographic Characteristics

Each parameter was measured according to standardized protocols. Sensory block was assessed using pinprick test with a 23G needle in the distribution of median, ulnar, radial, and musculocutaneous nerves, graded on a 0-2 scale. Motor block was evaluated using the modified Bromage scale for upper limb (0-2). Hemodynamic parameters were recorded at baseline and at regular intervals (5, 15, 30, 60, 90, 120, and 150 minutes) after the block. Pain was assessed using VAS and rescue analgesia requirements were recorded over 24 hours. Sedation was evaluated using the Ramsay Sedation Scale. Adverse effects were documented and managed according to standard protocols.

Table 2: Block Characteristics

*Statistically significant

Table 3: Postoperative Analgesia Parameters

*Statistically significant

Table 4: Adverse Effects

The findings of our study demonstrate that dexmedetomidine is superior to clonidine as an adjuvant to ropivacaine in ultrasound-guided supraclavicular brachial plexus block for upper limb surgeries. The dexmedetomidine group exhibited significantly faster onset and longer duration of both sensory and motor block compared to the clonidine group. These results align with those reported by Swami SS et al., who found that dexmedetomidine provided significantly faster onset and longer duration of sensory block compared to clonidine when used as adjuvants to bupivacaine in supraclavicular brachial plexus block.[7] The superior effect of dexmedetomidine can be attributed to its higher selectivity for α2-adrenergic receptors (α2:α1 ratio of 1620:1 for dexmedetomidine vs. 220:1 for clonidine)[5], which translates to more potent effects on peripheral nerve block characteristics. Brummett CM et al. demonstrated in an animal study that perineural dexmedetomidine added to ropivacaine enhances the duration of sensory and motor blockade by blocking the hyperpolarization-activated cation current, preventing the nerve from returning to its resting membrane potential.[8]

The dexmedetomidine group also demonstrated superior postoperative analgesia with significantly longer time to first rescue analgesia, lower pain scores at the time of rescue analgesia, and reduced analgesic requirements in the first 24 hours postoperatively. These findings are consistent with those reported by Das A et al. and Gandhi R et al., who found that dexmedetomidine provided significantly longer postoperative analgesia compared to clonidine when used as adjuvants in brachial plexus blocks.[9,10] The enhanced analgesic efficacy of dexmedetomidine can be attributed to both peripheral and central mechanisms. Peripherally, dexmedetomidine reduces norepinephrine release and prevents nerve impulse propagation by hyperpolarization of post-synaptic dorsal horn neurons. Centrally, it activates α2-adrenoceptors in the locus coeruleus, leading to inhibition of adenylyl cyclase and reducing pain transmission.[11] El-Boghdadly K et al., in their systematic review and meta-analysis, found that dexmedetomidine was associated with reduced pain scores and analgesic consumption in the early postoperative period compared to control groups, further supporting our findings.[12]

The hemodynamic stability observed in both groups, along with the low incidence of adverse effects, supports the safety profile of both adjuvants when used in appropriate doses for peripheral nerve blocks. Although the dexmedetomidine group exhibited higher sedation scores, the level of sedation was mild to moderate (Ramsay Sedation Score of 2-3) and clinically acceptable, potentially beneficial in the perioperative setting by reducing patient anxiety without causing respiratory depression. Vorobeichik L et al. found that perineural administration of dexmedetomidine was associated with less pronounced hemodynamic effects compared to intravenous administration, supporting our approach of using perineural dexmedetomidine to maximize local effects while minimizing systemic side effects.[13] The relatively low incidence of adverse effects in our study can be attributed to several factors, including the use of ultrasound guidance for precise needle placement, careful dose selection of adjuvants, and exclusion of patients with significant comorbidities who might be more susceptible to adverse hemodynamic effects.

Based on our findings, dexmedetomidine (1 μg/kg) is superior to clonidine (2 μg/kg) as an adjuvant to ropivacaine (0.5%) in ultrasound-guided supraclavicular brachial plexus block for patients undergoing upper limb surgeries. Dexmedetomidine provides faster onset, longer duration of analgesia, better quality of pain relief, and a favorable side effect profile, making it the preferred adjuvant for improving postoperative pain management in these patients. The hemodynamic stability and low incidence of adverse effects observed with both adjuvants support their safety profile when used in appropriate doses for peripheral nerve blocks. The mild to moderate sedation associated with dexmedetomidine may be considered beneficial in the perioperative setting as it enhances patient comfort without causing respiratory depression.

1.      Neal JM, Gerancher JC, Hebl JR, Ilfeld BM, McCartney CJ, Franco CD, et al. Upper extremity regional anaesthesia: essentials of our current understanding, 2008. Reg Anesth Pain Med. 2009;34(2):134-70.

2.      Kapral S, Krafft P, Eibenberger K, Fitzgerald R, Gosch M, Weinstabl C. Ultrasound-guided supraclavicular approach for regional anaesthesia of the brachial plexus. Anesth Analg. 1994;78(3):507-13.

3.      Liu FC, Liou JT, Tsai YF, Li AH, Day YY, Hui YL, et al. Efficacy of ultrasound-guided axillary brachial plexus block: a comparative study with nerve stimulator-guided method. Chang Gung Med J. 2005;28(6):396-402.

4.      Eisenach JC, De Kock M, Klimscha W. Alpha(2)-adrenergic agonists for regional anaesthesia. A clinical review of clonidine (1984-1995). Anesthesiology. 1996;85(3):655-74.

5.      Virtanen R, Savola JM, Saano V, Nyman L. Characterization of the selectivity, specificity and potency of medetomidine as an alpha 2-adrenoceptor agonist. Eur J Pharmacol. 1988;150(1-2):9-14.

6.      Sangita Mandal, Sanjay Maitra, Abhijit Mukherjee, & Mandal, M. (2022). Clonidine and dexmedetomidine as adjuvant to ropivacaine for supraclavicular brachial plexus block during upper limb surgery: A comparative study. Asian Journal of Medical Sciences, 13(7), 34–42.

7.      Swami SS, Keniya VM, Ladi SD, Rao R. Comparison of dexmedetomidine and clonidine (α2 agonist drugs) as an adjuvant to local anaesthesia in supraclavicular brachial plexus block: A randomised double-blind prospective study. Indian J Anaesth. 2012;56(3):243-9.

8.      Brummett CM, Hong EK, Janda AM, Amodeo FS, Lydic R. Perineural dexmedetomidine added to ropivacaine for sciatic nerve block in rats prolongs the duration of analgesia by blocking the hyperpolarization-activated cation current. Anesthesiology. 2011;115(4):836-43.

9.      Das A, Majumdar S, Halder S, Chattopadhyay S, Pal S, Kundu R, et al. Effect of dexmedetomidine as adjuvant in ropivacaine-induced supraclavicular brachial plexus block: A prospective, double-blinded and randomized controlled study. Saudi J Anaesth. 2014;8(Suppl 1).

10.   Gandhi R, Shah A, Patel I. Use of dexmedetomidine along with bupivacaine for brachial plexus block. Natl J Med Res. 2012;2(1):67-9.

11.   Eisenach JC, De Kock M, Klimscha W. Alpha(2)-adrenergic agonists for regional anaesthesia. A clinical review of clonidine (1984-1995). Anesthesiology. 1996;85(3):655-74.

12.   El-Boghdadly K, Brull R, Sehmbi H, Abdallah FW. Perineural Dexmedetomidine Is More Effective Than Clonidine When Added to Local Anaesthetic for Supraclavicular Brachial Plexus Block: A Systematic Review and Meta-analysis. Anesth Analg. 2017;124(6):2008-20.

13.   Vorobeichik L, Brull R, Abdallah FW. Evidence basis for using perineural dexmedetomidine to enhance the quality of brachial plexus nerve blocks: a systematic review and meta-analysis of randomized controlled trials. Br J Anaesth. 2017;118(2):167-81.