Wongswadiwat, M., J. Kuanratikul, S. Thienthong, S. Ponjanyakul, P. Ratanasuwan Yimyaem, and W. Sriraj. “The Effectiveness of Spinal Morphine Plus Intravenous Patient-Controlled Analgesia on Postoperative Pain Controlled at Srinagarind Hospital”. Srinagarind Medical Journal, vol. 24, no. 3, Nov. 2013, pp. 190-6, https://li01.tci-thaijo.org/index.php/SRIMEDJ/article/view/13018.