This prospective, randomized, comparative study was approved by the institutional ethics committee at KPC Medical College and Hospital, Kolkata (No. KPCMH/Ethics/19/184 dated 01/07/2019) and was registered in the clinical trial registry - India (CTRI/2021/02/031042). All procedures performed in the study were in accordance with the ethical guidelines of the declaration of Helsinki. Before inclusion in the study, voluntary written informed consent was obtained from all participants.
Forty one American Society of Anaesthesiologists (ASA) grade I and II patients older than 18 years of age presenting for shoulder arthroscopic surgery were included in the study. Patients who were allergic to the medications used in this study, those with a contraindication to peripheral nerve block (puncture site infection, bleeding disorders), those who did not understand the visual analogue scale (VAS), or those who refused for the nerve block were excluded from the study.
During the pre-anaesthesia consultation, the study and procedure were explained to the patients in their own language and a written informed consent was obtained. Upon arrival in the operating room, monitoring lines for electrocardiogram (ECG), noninvasive blood pressure (NIBP), pulse oximetry (SpO2) were attached and an 18 or 20-G peripheral venous cannula was placed in the opposite upper limb to start an infusion of ringer lactate. With the help of computer generated randomization patients were divided in two groups - Group S (n=20) in which patients received SSNB alone and Group C (n=21) in which patients received a combined block (SSNB + ANB).
Performing the Blocks:
Suprascapular nerve block: SSNB was performed using the technique of Meier [5] with the aid of a peripheral nerve stimulator (Stimuplex HNS 12). With the patient in the sitting position and arm in complete adduction, a line connecting the lateral part of the acromium and the medial end of the spine of the scapula was established. A 22 guage, 10 cm insulated needle was inserted at a point located 2 cm medial and 2 cm cephalad to the midpoint of this line. The direction of the needle was lateralocaudal (45° in the coronal plane), with a ventral lean of about 30°. After the stimulation of infraspinatous muscle was achieved at the initial current of 1.5 mA and then at 0.5 mA, 10 mL of 0.5% ropivacaine was injected slowly after negative aspiration.
Axillary nerve block: ANB was performed using the technique of Price [6] with the aid of a peripheral nerve stimulator (Stimuplex HNS 12). With the patient in sitting position and arm in adduction, a line joining the anterior aspect of the acromium and the inferior angle of the scapula was drawn across the skin. From the midpoint of this line a horizontal line was drawn laterally. From the postero-lateral aspect of the acromium, a vertical line was traced down right behind the humerus. The point of intersection of this line with the horizontal line was the needle puncture site where a 22 guage, 10 cm insulated needle was passed straight anterior, towards the posterior aspect of the humerus. At the depth of 6-8 cm with a current of 1.5 mA twitches in the anterior deltoid were observed which were further confirmed with a current of 0.5 mA and 10 mL of 0.5% ropivacaine was injected slowly.
After the block, patients were monitored for 15 minutes before giving general anaesthesia and the success of block was assessed by testing for cold sensation using spirit soaked cotton swab along the distribution of suprascapular and axillary nerves.
General anaesthesia:
After preoxygenation, induction was done with injection propofol 2 mg kg-1; relaxation was achieved with injection rocuronium to facilitate intubation. Fentanyl 2 µg kg-1 was used for intraoperative analgesia. Anaesthesia was maintained with nitrous oxide, oxygen and sevoflurane. Thirty minutes before extubation all the patients received 20 mg kg-1 paracetamol intravenously. Neostigmine with glycopyrrolate was used to reverse the muscle relaxation; patients were shifted to recovery room after extubation.
Parameters observed:
Post-operative pain was assessed using VAS (at rest and during movement) at 1 hour, 3 hours, 6 hours, 12 hours and 24 hours after surgery. The 11 point VAS ranged from 0 (no pain) to 10 (worst imaginable pain). VAS was also noted when patients demanded the analgesic for the first time.
All the patients were given injection pethidine 1.5 mg kg-1, upto 100 mg, intramuscularly when they demanded or when VAS was 4 or more and the total consumption of the drug in the 24 hours was noted.
Patient satisfaction was assessed on a three point scale with 1 (dissatisfied), 2 (moderately satisfied) and 3 (highly satisfied) at 12 hours and 24 hour postoperatively.
Patients were also monitored for any adverse effects for the 24 hours like nausea, vomiting, respiratory depression, itching, etc.
Sample size calculation and statistical analysis: To have an adequate study power the required sample size was calculated using Clin Calc, an online sample size calculator (www.clincalc.com/stats/samplesize.aspx). Considering an alpha level (probability of type I error) of 0.05 and beta level (probability of type II error) of 0.05 to establish the desired power of 95%, 20 patients were required for each group. 10% i,e four patients were added in anticipation of attrition. So a total of 44 patients were included in the study. The normal (Gaussian) distribution of the data was determined using Shapiro-Wilk test and statistical significance was analyzed by Student’s t-test, Mann-Whitney U test, and Fisher’s exact test using GraphPad PRISM 9, a p value <0.05 is considered significant.