Tehran University of Medical Sciences Archives of Anesthesiology and Critical Care 2423-5849 8 2 2022 04 09 134 138 Kalyani Patil Department of Anaesthesiology, Smt. Kashibai Navale Medical College and General Hospital, Pune, India. Jyoti Deshpande Department of Anaesthesiology, Smt. Kashibai Navale Medical College and General Hospital, Pune, India. Rajlaxmi Menghal Department of Anaesthesiology, Smt. Kashibai Navale Medical College and General Hospital, Pune, India. Lavina John Department of Anaesthesiology, Smt. Kashibai Navale Medical College and General Hospital, Pune, India. 2021 11 09 2021 12 21 Background: Interscalene block is a commonly performed procedure for surgery of shoulder and upper arm, however very few studies have studied the effect of magnesium sulphate when added in interscalene block. Aims: The primary aim was to compare block characteristics along with postoperative analgesia and the secondary aim was to study the side effect profile and postoperative analgesic requirements. Methods: We randomly recruited 60 American Society of Anaesthesiologists (ASA) physical status I and II patients, undergoing surgeries of the shoulder to receive ultrasound-guided interscalene block with 1 mL normal saline or 150 mg Magnesium sulphate added to 20ml of 0.5% ropivacaine. Statistical analysis used: Statistical Package for Social Sciences (SPSS version 21.0) was used for analysing the data. Chi-square test or Fisher’s exact probability test were used for categorical variables; while the continuous variables were compared by unpaired t-test or Mann-Whitney U test. Results: With the addition of magnesium sulphate, onset of sensory (10.03 ± 1.03 vs 12.73 ± 1.14 min) and motor block (15.17 ± 2.02 min vs 17.87 ± 1.41) was hastened. The duration (sensory 528.00 ± 14.98 min vs 376.83 ± 13.16 min, motor 429.83 ± 11.57 min vs 319.97 ± 6.800 min) and postoperative analgesia (527.77 ± 21.96 min vs 402.97 ± 12.83 min) (p < 0.001) were all prolonged by magnesium sulphate, with resultant decrease in requirement of postoperative analgesic dosage. Conclusion: Magnesium when added to local anaesthetics in interscalene block, effectively improves all characteristics of block and provides better postoperative analgesia. https://aacc.tums.ac.ir/index.php/aacc/article/view/429