Singh, S., M. K. Giri, M. Singh, and N. K. Giri. “A Clinical Comparative Study of Intraperitoneal Instillation of Ropivacaine Alone or Ropivacaine With Nalbuphine for Postoperative Analgesia in Laparoscopic Cholecystectomy”. Anaesthesia, Pain & Intensive Care, Jan. 2019, pp. 335-9, https://mail.apicareonline.com/index.php/APIC/article/view/135.