Sapate, M., P. Sahu, W. S. Thatte, and R. Dubey. “A Randomized, Double Blind, Control Study of the Effects of Adding Nalbuphine to Spinal Bupivacaine for Lower Abdominal Surgeries in Elderly Patients”. Anaesthesia, Pain & Intensive Care, Jan. 2019, pp. 145-8, https://apicareonline.com/index.php/APIC/article/view/457.