385: Is Standard Ward Surveillance Enough? Respiratory Safety Outcomes from Intra-operative Methadone

Topic: Clinical Science
Subtopic: Pain category (ICD-11), Acute postsurgical pain, Pharmacological treatments

Background and Aims: Intra-operative Methadone has gained increasing interest as a long-acting perioperative analgesic; however, concerns remain regarding delayed postoperative respiratory depression due to its prolonged elimination half-life and interpatient pharmacodynamic variability. In 2025, Austin Hospital introduced an institutional perioperative methadone guideline mandating increased postoperative ward observations (hourly for 4 hours). We sought to evaluate early prescribing patterns and respiratory safety outcomes following implementation.

Methods: A retrospective audit was performed of all adult patients administered intra-operative Methadone between 1 June and 31 December 2025. Electronic medical record review captured type of surgery, weight-adjusted methadone dose, chronic pain status, concurrent regional analgesia use, compliance with enhanced postoperative ward observations (hourly for four hours following discharge from post-anaesthesia care), and clinically significant respiratory adverse events defined by either emergency medical review or naloxone administration.

Results: Among 246 patients receiving intra-operative Methadone, utilisation was concentrated in major surgery, including cardiac (37%), open abdominal (17%), joint (10%), and spinal fusion procedures (9%). Overall median methadone dose was 0.19 mg/kg (IQR 0.13–0.23). Cardiac surgery patients received significantly higher weight-adjusted dosing (0.22 mg/kg, IQR 0.19–0.26), likely reflecting both higher predicted nociceptive insult and the safety conferred by routine postoperative intensive care unit admission. Chronic pain prevalence (15%) was not associated with altered methadone dose selection (p=0.121), whereas concomitant regional analgesia was associated with lower methadone dosing (p=0.001). Compliance with mandated increased ward observations was 74%. Despite this enhanced monitoring pathway, two patients experienced postoperative respiratory depression requiring naloxone administration and emergency medical team review, corresponding to an incidence of 0.83%.

Conclusions: Clinically significant respiratory depression occurred in approximately 1 in 120 patients following intra-operative methadone across the study period. This incidence appears higher than published naloxone-reversal rates for conventional perioperative opioids, suggesting that intermittent ward-based observations alone may be insufficient to detect or prevent delayed methadone-related respiratory compromise. Enhanced patient selection, dose governance, and consideration of continuous postoperative respiratory monitoring may be warranted with institutional methadone adoption.

References: Murphy GS, Szokol JW, Avram MJ, Greenberg SB, Shear TD, Deshur MA, et al. Intraoperative methadone for the prevention of postoperative pain: a randomized, double-blinded clinical trial in cardiac surgical patients. Anesthesiology. 2015;122(5):1112-1122. doi:10.1097/ALN.0000000000000633.

Edwards JN, Whitney MA, Smith BB, Fah MK, Buckner Petty SA, Durra O, et al. The role of methadone in cardiac surgery for management of postoperative pain. BJA Open. 2024;10:100270. doi:10.1016/j.bjao.2024.100270.

Dunn LK, Yerra S, Fang S, Hanak MF, Leibowitz MK, Tsang S, et al. Safety profile of intraoperative methadone for analgesia after major spine surgery: an observational study of 1,478 patients. J Opioid Manag. 2018;14(5):339-346. doi:10.5055/jom.2018.0435.

Lumsden SL, Beard C, McCartney CJL, Katz J, Clarke H. Intraoperative methadone administration is not associated with an increase in perioperative use of naloxone: a retrospective study. Anesth Analg. 2024;138(2):321-329. doi:10.1213/ANE.0000000000005143.

Presenting Author: Amass Zheng, Yuan Yi
Submitting Author: Yuan Yi

Senior Author: Yuan Yi

IASP 2026 Global Year theme of Neuropathic Pain: No

• Amass Zheng: M.D. - Austin Health
• Areeb Athar: M.D. - Austin Health