Comparison of the efficacy of two doses of dexmedetomidine as an adjunct to levobupivacaine in infraclavicular brachial plexus block: prospective double-blinded randomized controlled trial

Ethics and registration

This study was approved by the Ethics Committee of Aswan University Hospital (approval number: aswu/125/4/17) (date of registration: 04/04/2017). Furthermore, this trial was retrospectively registered at ClinicalTrial.gov (NCT04729868) with a verification date of January 2021. Participants were aware of the study's objectives, risks, and benefits before signing a written informed consent form. All methods were performed according to the guidelines of the Declaration of Helsinki and its later amendments.

Patient inclusion and exclusion criteria

Patients aged 20–60 years of both sex who had an American Society of Anesthesiologists (ASA) physical status of I/II and scheduled for forearm and hand surgery were recruited. Patients with a history of brachial plexus injury, coagulopathy, allergy to the study drugs, hepatic or renal insufficiency, respiratory or cardiac disorders, seizures, pregnancy, or local infections at the site where the block needle was to be inserted were excluded from the study.

Randomization

Randomization was established using computer-generated randomization tables to allocate patients into one of three equal groups, and the group allocation was concealed in sealed opaque envelopes. Patients were allocated into one of three equal groups: the L group consisted of patients who received anesthesia with 35-mL 0.5% levobupivacaine plus 1 mL normal saline; the LD50 group included patients who received anesthesia with 35-mL 0.5% levobupivacaine plus 50-µg dexmedetomidine, and the LD100 group included patients who received anesthesia with 35-mL 0.5% levobupivacaine plus 100-µg dexmedetomidine.

An investigator who was not involved in either the block performance or the outcome evaluation received serially numbered sealed envelopes labeled L, LD50, or LD100 for preparing the anesthetic mixture to be administered. The total volume of dexmedetomidine was adjusted to 1 ml to ensure that the same volume of the anesthetic mixture was used for all groups. The patients, operator performing the block, and data collectors were blinded to the group assignment.

Anesthesia

The procedure was fully explained to the patients primarily for ethical aspects and to ensure cooperation and acceptance of being awake during surgery. Moreover, the visual analog scale (VAS) was explained (the VAS is a straight, vertical 10-cm line with the bottom point representing “no pain” (0 cm) and the top point representing “the worst pain you could ever have” (10 cm). Before the procedure, for a minimum of 6 h, all patients were given nothing by mouth. Standard monitoring using an electrocardiogram, noninvasive blood pressure, and pulse oximetry (SpO2) was connected to the patients upon arrival at the operating room, and the displayed data were recorded before surgery. A 20-G cannula was inserted into the contralateral hand, and Ringer’s lactate was infused. Patients were sedated using 0.05-mg/kg intravenous midazolam hydrochloride and fentanyl in doses ranged from 0.5 to 1 μg/kg based on the patient response. During surgery, a nasal catheter with a 3-L/min oxygen supply was used.

The ultrasound-guided infraclavicular brachial plexus block was performed by a single trained author who was blinded to the nature of the anesthetic mixture. While the patient was supine and the arm was abducted to 90°, the deltopectoral region was scanned using an ultrasound machine (SonoScape, model A5, China) equipped with a high-frequency (> 10 MHz) linear probe. Then, a 20-G, 120-mm, non-cutting-tip echogenic needle (SonoPlex STIM, Germany) was introduced and advanced in-plane until imaged.

The needle was first aimed at the medial cord, which runs between the axillary artery and vein, and numbed using the injected LAs (12 ml). Then, the needle was guided to the lateral cord before injecting the LA solution (12 ml). It was then advanced to the posterior cord, and more LAs were deposited (12 ml). During injections, the operator sonographically tracked LAs around the cords and always kept the needle's image in view. The following anesthetic mixtures were administered according to the patient’s study group assignment: 35-mL 0.5% levobupivacaine plus 1 mL normal saline (control group), 50-μg or 100-μg dexmedetomidine (study groups).

Outcome measures

The primary endpoint was the duration of sensory blockade. In contrast, the secondary ones included the duration of motor blockade, sensory and motor blockade onset time, elapsed time to first postoperative request for rescue analgesia, postoperative analgesic needs in the first 24 h, hemodynamic monitoring, and sedation scores. All patients were evaluated for the following conditions:

• Sensory block duration (h) was the time elapsed between the onset of the sensory block and the restoration of sensation at the surgical site, while the time elapsed between the onset of the motor block and the restoration of global mobility in hand and wrist was measured as the duration of the motor block (h).

• Onset time of sensory blockade was measured by loss of sensation to a gauze soaked in normal iced saline using a 3-point scale: 0 = complete loss of sensation, 1 = partial loss of sensation, and 2 = normal sensation, along the middle of the dermatomal distribution of the musculocutaneous, median, radial, and ulnar nerves, and the onset time of motor blockade was measured using the modified Bromage scale (0 = normal motor function, 1 = reduced motor strength but able to move fingers, 2 = complete motor block) [13,14,15].

• Heart rate (beat/min), oxygen saturation, and mean arterial blood pressure (mmHg) were measured before the block; 5, 10, 20, 30, 40, 50, and 60 min after the block; and 6, 12, and 24 h later.

• VAS was used to rate pain control at the 1st, second, fourth, sixth, 12th, and 24th hours after surgery. When the VAS reached 3 cm, rescue analgesia in the form of 0.05-mg/kg morphine sulfate was administered intravenously; time to the first postoperative request for rescue analgesia and the total morphine consumption in the first 24 h were recorded.

• The Modified Ramsay Sedation Scale (m-RSS) was used to assess the sedation score every hour until four hours after the block [16].

• The patients were examined for any complications that could arise during or after the procedure. Bradycardia was defined as a heart rate of fewer than 50 beats per minute and was treated with a 0.5–1-mg intravenous bolus of atropine. Hypotension was described as a 30% decrease in the mean arterial pressure (MAP) from baseline or MAP less than 60 mmHg and was treated with 6-mg intravenous ephedrine in increments as needed.

Sample size and statistical analysis

Based on a pilot study involving 15 patients, the sample size was calculated using G*Power 3 software. The primary outcome measure in this study was the duration of sensory blocks. The minimum sample size for a one-tailed test with a power of 80% and a type I error of 5% (α = 0.05 and β = 80%) was 54 people divided into three equal groups. Each group required 18 patients to detect a 0.5 effect size in the mean duration of the sensory block (8, 12, and 14 h). We added 10% of the total study population to compensate for dropouts.

Data were analyzed using Statistical Package for the Social Sciences (version 26; IBM Corp., Armonk, NY, USA). Normality tests (the Kolmogorov–Smirnov, and Shapiro–Wilk tests) were performed, and data (i.e., age, ASA physical status, duration of surgery, duration of sensory blockade, the onset of sensory blockade, duration of motor blockade, the onset of motor blockade, time to the first request for postoperative rescue analgesia, total postoperative morphine sulfate needs, mean arterial blood pressure, mean heart rate, and arterial oxygen saturation) were normally distributed. In contrast, data on VAS were not normally distributed. Nominal data were expressed as percentages; differences between all groups under study were detected using the chi-square test. Continuous data were expressed as mean ± standard deviation or median (range). Differences between all groups under study were detected using one-way ANOVA; multiple comparisons between every two groups were detected using the least significant difference (LSD) post hoc multiple comparisons for parametric data. In contrast, differences between all groups under study were detected using the Kruskal–Walls test; multiple comparisons between every two groups were detected using the Mann–Whitney test for nonparametric data. Spearman’s correlation coefficients were used to analyze the correlation between different parameters within the groups under study. Kaplan–Meier curve was used to estimate the median survival time. The Log-rank test was used to compare survival curves between the categories of the explanatory variables. P-values of less than 0.05 were used to denote statistical significance.

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