A comparative study of buprenorphine in two different doses as an adjuvant to levobupivacaine in US-guided lumbar plexus block for postoperative analgesia .Authors:Vaibhav Tulsyan, Jai Singh, Lokesh Thakur, Versha Verma* and Ashish Minhas Ain-Shams Journal of Anesthesiology 2021; 13:7