The purpose of this study is to investigate whether perioperative intravenous acetaminophen administration reduces postoperative pain and opioid consumption in adolescents and pediatric patients undergoing spinal fusion surgery.

Spinal fusion surgery to correct scoliosis causes severe postoperative pain in adolescents and pediatric patients. Thus, appropriate control of postoperative pain has a significant impact on postoperative recovery, patient satisfaction and reduction of hospital stay. Although pain control was achieved through only opioids, the importance of multimodal analgesia has recently been emphasized as opioid addiction and side effects increase.

Acetaminophen is recommended as a key factor in multimodal analgesia and previous studies performed in adult spine surgery showed that intravenous administration of acetaminophen reduced the postoperative pain and opioid consumption. In addition, acetaminophen is a drug widely recognized for safety in adolescents and pediatric patients and has a fast and predictable analgesic effect. Therefore, the purpose of this study is to investigate whether perioperative intravenous acetaminophen administration reduces postoperative pain and opioid consumption in adolescents and pediatric patients undergoing spinal fusion surgery. Thus the specific aim of this trial the investigators will determine is;

1. The decrease in postoperative analgesic requirement following IV acetaminophen
2. The decrease in intensity of postoperative pain following IV acetaminophen
3. The quality of recovery including self-reported recovery, physical and functional recovery and length of stay
4. The preemptive analgesic effect of IV acetaminophen

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) physical status 1-3
• patients undergoing spinal fusion surgery

Exclusion Criteria:

• patients who refuse to participate in this study
• patients unable to communicate due to mental impairment or developmental delay
• patients allergic to acetaminophen or its additives or who are contraindicated in acetaminophen administration for other reasons
• patients with existing liver diseases or dysfunction (i.e. active hepatitis, clinically relevant chronic liver conditions, elevated liver enzymes)
• patients who are judged ineligible by the medical staff to participate in the study for other reasons

The designated research pharmacist will prepare the both study drug (IV acetaminophen) and placebo and will dispense the study drug according to treatment allocation. Treatment allocation will remain concealed from all other investigators involved in the conduct and analysis of the trial. All other medical staff involved in patient care during the hospital stay of study participant and the study participants itself along with guardians will be also blinded throughout.