Dexmedetomidine and Magnesium Sulfate as Adjuvant to 0.5% Ropivacaine in Supraclavicular Brachial Plexus Block: A Comparative Evaluation.

BACKGROUND: Dexmedetomidine and magnesium sulfate (MgSO4) as an adjuvant to local anesthetics and ultrasound guidance improves the quality of peripheral nerve block. AIM: We aim to compare the efficacy of dexmedetomidine and MgSO4 as an adjuvant to ropivacaine in supraclavicular brachial plexus block.
METHODOLOGY: Sixty patients undergoing upper extremity orthopedic surgery were randomly allocated into three groups of 20 each. Group A received 29 mL of 0.5% ropivacaine plus 1 mL of normal saline, Group B received 29 mL of 0.5% ropivacaine plus 1 mL dexmedetomidine (100 μg), and Group C received 29 mL of 0.5% ropivacaine plus 1 mL MgSO4 (250 mg). Onset and duration of sensory and motor block, duration of analgesia, quality of anesthesia, total 24 h analgesic consumption, sedation, and complications were recorded. STATISTICAL ANALYSIS: Software SPSS-16 was used for statistical analysis.
RESULTS: The onset of sensory block and motor block was fastest for Group B, followed by Group C and slowest in Group A. The duration of sensory block and motor block was maximum for Group B, followed by Group C and minimum for Group A. The duration of analgesia was maximum for Group B, followed by Group C and minimum for Group A. Analgesic consumption was minimum for Group B. Quality of anesthesia was better in Group B than other groups. The visual analog scale was higher in Group A than other groups. Group B reported higher sedation score.
CONCLUSION: Dexmedetomidine provides earlier onset of sensory and motor block as well as prolonged duration of sensory and motor blocks and duration of analgesia is longer and postoperative rescue analgesia is less as compared to patients receiving MgSO4. The incidence of hypotension and bradycardia and sedation score was higher with dexmedetomidine. Copyright:

INTRODUCTION

Supraclavicular brachial plexus block is a better alternative to general anesthesia in surgeries of the elbow, forearm, wrist, and hand.[1] Brachial plexus blockade reduces the pain, but due to short duration, the challenge remains to increase the duration of analgesia with decreasing side effects. A variety of perineural adjuvants[23] have been tried to hasten the time of onset and prolong the duration of analgesia of nerve blocks with varying degrees of success. Ropivacaine is a local anesthetic effective for both intraoperative anesthesia and postoperative analgesia. For peripheral nerve blockade, ropivacaine is comparable to bupivacaine and levobupivacaine.[45] However, the lower lipid solubility of ropivacaine causes greater sensory and motor differential blockade.[6] Dexmedetomidine, an α2 adrenoreceptor agonist, has proved to be a useful additive to local anesthetics in peripheral nerve blocks.[78] The combination of dexmedetomidine and ropivacaine has been associated with a significant prolongation of the duration of the sensory blockade and postoperative pain relief. Magnesium sulfate (MgSO4) has N-methyl-D-aspartate receptor antagonist property.[9] Magnesium exerts antinociceptive effects by regulation of calcium influx into the cell. Magnesium has antihypertensive, anesthetic sparing effects and its property to enhance the effects of analgesics. The aim of this prospective, double-blind randomized controlled clinical study was to compare the efficacy of dexmedetomidine and MgSO4 as an adjuvant to ropivacaine in ultrasound-guided supraclavicular brachial plexus block for upper limb surgeries in terms of onset, duration of sensory and motor blocks, and duration of analgesia.

METHODOLOGY

This prospective randomized double-blinded study was conducted in the Department of Anesthesiology, U. P. U. M. S, Saifai, Etawah (U. P) from November 2018 to April 2020 after the Institutional Ethical Committee Approval (E. C. NO: 129/2018). Preanesthetic checkup was done. Informed and written consent was taken from patients posted for upper limb surgery of ASA classes I and II, of either sex, between the age group of 19 and 60 years. Patients with hypersensitivity or allergy, malignancy, dementia/confusion, coagulopathies, local area of infection, and surgery more than 3 h, were excluded from the study. Sample size calculation was done based on 95% confidence interval, 5% alpha error using G power Software, and a total of 60 patients were selected and randomized into three study groups of 20 patients each according to computer-generated code.

Group A (n = 20): 29 mL of 0.5% ropivacaine plus 1 mL of normal saline in supraclavicular brachial plexus block

Group B (n = 20): 29 mL of 0.5% ropivacaine plus 1 mL dexmedetomidine (100 μg) supraclavicular brachial plexus block

Group C (n = 20): 29 mL of 0.5% ropivacaine plus 1 mL MgSO4 (250 mg) supraclavicular brachial plexus block.

The total study drug volume used was 30 mL in each group. In the operation theater, standard monitors including electrocardiography, noninvasive blood pressure, and pulse oximeter were attached and recorded. An intravenous (i.v.) line with 18 G cannula was secured in the unaffected limb and i.v. crystalloid infusion at the rate of 5 mL.kg.−1.h−1 will be started. Sonosite Fujifilm ultrasound system with HFL38/8-12 MHZ transducer was used for ultrasound guidance. The block was performed with the patients in the supine position with the patient's head turned away from the side to be blocked. The skin was disinfected and the transducer positioned in the transverse plane immediately superior to the clavicle at approximately its midpoint. Using a 25- to 27-gauge needle, 1–2 mL of local anesthetic was injected into the skin 1 cm lateral to the transducer. The block needle is then inserted in-plane toward the brachial plexus, in a lateral to medial direction. After negative aspiration 1-2 ml of drug was injected to document the proper needle placement, then remaining drug was injected.

Patients were monitored throughout the surgery, at the time of application of block, and thereafter up to 24 h after the surgery. The primary outcome was measured; heart rate and mean arterial blood pressure and Spo2 were recorded at baseline and thereafter 5th, 10th, 15th, 30th, 60th, 90th, 120th, 150th, 180th min and then 6th, 12th, and 24th h postoperatively. Sensory block was assessed by pinprick test using the blunt end of a 26-gauge needle at each minute after completion of drug injection in the dermatomal areas corresponding to the median nerve, ulnar nerve, radial nerve, and musculocutaneous nerve till complete blockade using a 3-point scale: 0 – normal sensation, 1 – loss of sensation of pinprick (analgesia), and 2 – loss of sensation of touch (anesthesia). Onset time is defined as the time interval between the end of total local anesthetic administration and complete sensory block. Duration of sensory block is defined as the time interval between the end of local anesthetic administration and the complete resolution of anesthesia. Motor blockade was assessed by Modified Bromage Scale at each minute after completion of drug injection. The Motor block was graded according to modified bromage scale: 0 = normal motor function, 1 = ability to move only fingers, 2 = complete motor block with inability to move the elbow and/or wrist and/or finger. Motor block onset time is defined as the time interval between the end of total local anesthetic administration and complete motor block. Duration of motor block is defined as the time interval from the onset to the recovery of complete motor function.

Duration of analgesia

Patient pain was evaluated by visual analog scale (VAS), a scale of 0 to 10, where 0 is no pain and 10 is very severe pain. In all the three groups, time to injection was considered as time zero; VAS at time zero was the baseline score and was recorded in all patients. When VAS ≥3, supplement analgesia injection diclofenac sodium 1.5 mg.kg−1 intramuscular was administered. The time for the first request for the analgesic requirement was noted. The total analgesic requirement in the first 24 h was also noted. Sedation was assessed using Ramsay sedation score (RSS) (1 = anxious, agitated, and restless, 2 = cooperative, oriented, and tranquil, 3 = responsive to commands only, 4 = asleep but has brisk response to light glabellar tap or loud auditory stimulus, 5 = sluggish response to light glabellar tap or loud auditory stimulus, and 6 = no response to light glabellar tap or loud auditory stimulus). At the end of the operation, quality of anesthesia was graded as: excellent (4) = no complaint from the patient, good (3) = minor complaint with no need for supplemental analgesics, moderate (2) = complaint that required supplemental analgesics, and unsuccessful (1) = patient required general anesthesia. Patients were assessed for intraoperative and postoperative complications. Intraoperative bradycardia (<50 beats/min) occurred and managed with injection atropine 0.6 mg i.v and hypotension (>20% below baseline value) managed with injection mephentermine 6 mg intravenously.

Statistical analysis

The results were presented in frequencies, percentages, and mean ± standard deviation. The Chi-square test was used to compare categorical variables among the groups. The one-way analysis of variance (ANOVA) test, followed by Tukey's post hoc tests was used to compare continuous variables among the groups. P < 0.05 was considered statistically significant. All the analysis was carried out on SPSS 16.0 version (Inc., Chicago, IL, USA).

RESULTS

Sixty patients were enrolled in the study; two patients failed to achieve block and hence were excluded from the study. Hence, the analysis was done by taking the total number of 19 patients in Group A, 20 patients in Group B, and 19 patients in Group C [Figure 1]. All the groups were found comparable in terms of demographic profile, anthropometric parameters, duration of surgery, and ASA physical classes [Table 1].

Figure 1

Consort flow diagram of participants through each stage of a randomized trial

Table 1

Demographic characteristics and operative data

Characteristics	Group A (n=19)	Group B (n=20)	Group C (n=19)	P
Age (years) (Mean±SD)	35.90±12.19	37.35±11.36	40.85±11.20	0.38
Weight (Kg)(Mean±SD)	62.55±11.36	64.85±10.86	65.50±11.03	0.67
Duration of surgery (min) (Mean±SD)	132.00±20.41	132.00±22.61	130.50±20.12	0.96
ASA (I: II)	11:8	13:7	12:7	0.89
Sex (Male: Female)%	73.7:26.3	65.0:35.0	68.4:31.6	0.84

SD=Standard deviation, P<0.05 Significant ASA=American Society of Anesthesiologist

The onset of sensory block was fastest for Group B (5.60 ± 1.27 min), followed by Group C (7.65 ± 1.69 min) and was slowest in Group A (16.10 ± 2.07 min). The time of onset of motor block was fastest in Group B (8.95 ± 1.31 min) than in Group C (11.35 ± 2.13 min) and was slowest in Group A (21.90 ± 3.95 min). The duration of sensory block was maximum for Group B (917.40 ± 103.17 min), followed by Group C (584.50 ± 71.57 min), minimum for Group A (339.75 ± 30.67 min). Similarly, the duration of motor block was maximum for Group B (827.55 ± 86.81 min), followed by Group C (543.30 ± 69.01 min) minimum for Group A (282.25 ± 23.97 min). The duration of analgesia was maximum for Group B (1018.85 ± 96.84 min), followed by Group C (635.40 ± 59.98 min) minimum for Group A (406.40 ± 48.69 min). The difference in terms of onset and duration of sensory and motor, duration of analgesia between the three groups was highly statistically significant. The amount of injection diclofenac sodium used was maximum for Group A (294.74 ± 77.98 min), followed by Group C (263.16 ± 76.08 min) minimum for Group B (210.00 ± 64.07 mg) [Table 2]. The quality of block in Group A was excellent in 12 patients (63.15%) and good in 7 patients (36.84%); in Group B, the quality was excellent in 16 patients (80%) and good in 4 patients (20%). In Group C, the quality was excellent in 11 patients (57.89%) and good in 8 patients (42.10%). Although the quality of anesthesia seems to be better in Group B than other groups, no statistically significant difference was found in the proportion of grades among the groups (P = 0.31). In our study, the VAS score was nil for all the patients up to 5 h. After that, there was a significant (P = 0.001) difference in VAS among the groups only at 6 h. The post hoc tests revealed that VAS was significantly (P = 0.001) higher in Group A (3.90 ± 0.30) than Group B (1.50 ± 0.51) and Group C (1.25 ± 0.75) at 6 h [Figure 2]. Group B reported higher sedation scores compared to Group C. ANOVA showed that there was a significant difference in RSS among the groups at 60 min (P = 0.001), 90 min (P = 0.03), and 120 min (P = 0.01). The post hoc tests revealed that RSS was significantly (P = 0.001) different between Group A and Group B and Group B and Group C [Figure 3]. There was no significant difference in heart rate and mean blood pressure among all groups [Figures 4 and 5]. Incidence of bradycardia and hypotension is more in dexmedetomidine (Group B) which was statically significant [Table 3].

Table 2

Comparison of study parameters between three groups

Time periods	Group A (n=19)	Group B (n=20)	Group C (n=19)	P1	P2
					A vs B	A vs C	B vs C
Onset of Sensory blockade (Min)	16.10±2.07	5.60±1.27	7.65±1.69	0.0001*	0.0001*	0.0001*	0.0001*
Duration of Sensory blockade (Min)	339.75±30.67	917.40±103.17	584.50±71.7	0.0001*	0.0001*	0.0001*	0.0001*
Onset of Motor blockade (Min)	21.90±3.95	8.95±1.31	11.35±2.13	0.0001*	0.0001*	0.0001*	0.0001*
Duration of Motor blockade (Min)	282.25±23.7	827.55±86.81	543.30±69.01	0.0001*	0.0001*	0.0001*	0.0001*
Duration of Analgesia (Min)	406.40±48.69	1018.85±96.4	635.40±59.98	0.0001*	0.0001*	0.0001*	0.0001*
Total analgesic (mg) in 24 h	336.84±59.72	210.00±64.07	263.16±76.08	0.0001*	0.0001*	0.004*	0.04*

1ANOVA test, 2Post-hoc test, *Significant

Figure 2

Comparison of visual analog scale among the groups across the time periods the time periods

Figure 3

Comparison of Ramsay Sedation Score among the groups across the time periods

Figure 4

Comparison of heart rate among the groups across the time period

Figure 5

Comparison of mean blood pressure among the groups across the time periods

Table 3

Comparison of adverse effects among the groups

Adverse effects	Group A (n=19)		Group B (n=20)		Group C (n=19)		P1
	No.	%	No.	%	No.	%
Nausea	1	5.3	2	10.0	1	5.3	0.76
Skin rash	1	5.3	1	5.0	0	0.0	0.59
Bradycardia	1	5.3	2	10.0	0	0.0	0.02*
Hypotension	1	5.3	4	20.0	0	0.0	0.03*
Sedation	0	0.0	5	25.0	0	0.0	0.06
Hypoxia	0	0.0	1	5.0	0	0.0	0.36
Dryness of mouth	0	0.0	1	5.0	0	0.0	0.36

1Chi-square test, *Significant

DISCUSSION

In our study, we observed that the addition of dexmedetomidine or MgSO4 to ropivacaine resulted in the early onset of sensory and motor blocks and prolonged the duration of sensory and motor blocks. The onset of sensory block and motor block was fastest for Group B (dexmedetomidine), followed by Group C (MgSO4) and was slowest in Group A. The duration of sensory block and motor block was minimum for Group A, followed Group C and was maximum for Group B. Nema et al.[9] conducted a prospective randomized double-blind study among 60 patients found that the time of onset of sensory block was early in the dexmedetomidine group (7.20 ± 2.483 min) as compared to the control group (14.20 ± 5.229 min) and also the time of onset of motor block was early in dexmedetomidine group (11.83 ± 3.824 min) as compared to control group (21.00 ± 8.566 min) which is in concordance to our study. Our study is also bolstered by many studies namely Bharti et al.,[10] Kathuria et al.,[11] and Das et al.[12] In all these studies, it was observed that the time of onset for sensory and motor block was early after adding dexmedetomidine to ropivacaine in the supraclavicular block.

In our study, the onset of sensory and motor block was significantly faster in the magnesium groups than in the ropivacaine alone group. The findings of our study were in accordance with a study by Mukherjee et al.[13] who observed that the addition of MgSO4 increases the onset time of sensory and motor block. Similar findings were also seen in a study conducted by Malleeswaran et al.[14] and Ekmekci et al.[15] In our study, we observed that the addition of dexmedetomidine or MgSO4 to ropivacaine resulted in prolonged duration of analgesia postoperatively. The duration of analgesia was minimum for Group A, followed by Group C and maximum for Group B. In a randomized double-blind controlled study conducted by Chinnappa et al.,[16] they found that the addition of dexmedetomidine to ropivacaine for supraclavicular block prolongs the duration of sensory and motor block in dexmedetomidine group (630.6 ± 208.2 and 545.9 ± 224.0 min) than ropivacaine group (400.8 ± 86.6 and 346.9 ± 76.9 min) and the duration of analgesia was shorter in ropivacaine group (411.0 ± 91.2 min) then dexmedetomidine group (805.7 ± 205.9 min) which is in concordance to our study. In our study, we observed that the amount of injection diclofenac sodium used was minimum for Group B, followed by Group C and was maximum for Group A. Mukherjee et al.[13] concluded that the total need for rescue analgesics was lower in the magnesium group (RM). Bharti et al.[10] concluded that the requirement for rescue analgesic during the 24 h postoperative period was less in the dexmedetomidine group (P < 0.0001).

The quality of the block better in Group B than other groups, but no statistically significant difference was found. VAS was significantly higher in Group A (3.90 ± 0.30) than Group B (1.50 ± 0.51) and Group C (1.25 ± 0.75) at 6 h (P = 0.001). The above findings are also supported by Mukherjee et al.[13] where postoperative VAS values at 24 h were significantly lower in the magnesium group. In our study, hemodynamic parameters were comparable among the groups. Similar findings were also seen in the study of Das et al.[12] We also observed few complications. Nausea was observed in two patients (10%) in Group B, one patient (5.3%) in Group A, and one patient (5.3%) in Group C. Sedation was observed in 5 patients out of 20 patients in Group B. In the study conducted by Bharti et al.,[10] patients who received dexmedetomidine were found more sedated for 2 h than the control group patients (P < 0.0001). Bradycardia was observed in a total of three patients, one patient (5.3%) in Group A and two patients (10.0%) in Group B. Incidence of bradycardia and hypotension is more in dexmedetomidine which was statically significant (P < 0.05). Significantly lower blood pressure in the dexemedetomidine group was reported in a study conducted byEsmaoglu et al.,[17] and Das et al.[12] Skin rashes were observed in two patients, one patient (5.3%) in Group A and one patient (5.3%) in Group B patients, but this difference was not found to be statistically significant. Hypoxemia and dryness of mouth were observed only in one patient (5.0%) in Group B.

Limitation

The sample size was small; so the findings with regard to the incidence of side effects or the hemodynamic changes as the primary outcome variable cannot be commented. We did not measure the levels of dexmedetomidine, and magnesium in the plasma that could have further supported the hypothesis that dexmedetomidine and magnesium have a peripheral action rather than centrally mediated.

CONCLUSION

Dexmedetomidine or MgSO4 is useful adjuvant to ropivacaine for supraclavicular brachial plexus block. Dexmedetomidine provides earlier onset of sensory and motor block as well as prolonged duration of sensory and motor blocks and duration of analgesia is longer and postoperative rescue analgesia is less as compared to patients receiving MgSO4. The incidence of hypotension and bradycardia and sedation score is higher with dexmedetomidine.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.