X. Le, M. L. Nguyen, D. T. Nguyen, T. H. Do, and H. G. Nguyen, “Combined nefopam-fentanyl use in PCA for postoperative analgesia in spinal surgery patients: a randomized, controlled, single-blind trial”, apic, vol. 28, no. 4, pp. 687-691, Aug. 2024.