Postoperative pain remains a common challenge after abdominal surgery despite the use of standard multimodal pain management strategies. Poorly controlled pain can delay recovery, limit early mobilisation, reduce patient comfort, and increase the risk of longer-term pain problems.
This study aims to develop a predictive model to better understand and anticipate patients' postoperative pain relief needs after abdominal surgery. The study will observe adults undergoing elective abdominal surgery and collect information on their pain scores, pain medication use, surgical characteristics, and recovery during the first 48 hours after surgery.
Participants will receive standard postoperative pain management according to usual clinical practice. The study will analyse patterns of rescue pain medication use, including when and how often additional pain relief is required after surgery. The collected information will be used to develop a model that can predict factors associated with increased pain medication requirements.
The goal of this research is to improve understanding of individual differences in postoperative pain and provide a foundation for more personalised pain management strategies in the future. The findings may help healthcare providers identify patients who are more likely to require additional pain relief and support the development of safer and more effective approaches to postoperative pain control.
Adult patients aged 18-75 years
American Society of Anesthesiologists (ASA) physical status I-III
Elective open or laparoscopic abdominal surgery under general anaesthesia
Expected postoperative ward or high-dependency unit (HDU) stay of ≥ 48 hours
Chronic opioid therapy, defined as regular opioid use for ≥ 4 weeks prior to surgery
Severe hepatic impairment (Child-Pugh Class B or C) or severe renal impairment (eGFR < 30 mL/min/1.73 m²)
Known allergy or hypersensitivity to morphine or any opioid analgesic
Cognitive impairment (documented diagnosis of dementia or delirium), language barrier, or communication deficit precluding reliable NRS self-report
Adults undergoing elective abdominal surgery under general anaesthesia will be enrolled in this prospective observational cohort study. The study population represents patients experiencing the early postoperative recovery phase, where pain trajectories and analgesic requirements vary substantially between individuals. Participants will be observed during the first 48 hours after surgery to characterise patterns of rescue analgesic use and postoperative pain. The study aims to develop a predictive model of postoperative analgesic requirements by integrating analgesic administration patterns with patient and surgical characteristics. The findings will support a better understanding of individual variability in postoperative pain management and provide a foundation for future personalised analgesic strategies.
Cohort
Prospective
Intravenous Morphine Patient-Controlled Analgesia
DrugParticipants will receive intravenous morphine via patient-controlled analgesia (PCA) as part of standard postoperative analgesic management following elective abdominal surgery. The study does not assign or modify analgesic treatment. Morphine PCA usage, including timing and dose of successful administrations, will be recorded to characterise postoperative analgesic requirements using repeated time-to-event modelling.
Rescue Analgesic Administration Events During the First 48 Hours After Abdominal Surgery
The number and timing of successful rescue analgesic events following elective abdominal surgery. A rescue analgesic event is defined as each successful patient-controlled analgesia (PCA) activation resulting in intravenous morphine delivery. The repeated occurrence and timing of rescue analgesic events will be analysed using repeated time-to-event modelling to characterise postoperative analgesic requirements.
Postoperative Pain Scores
Pain intensity measured using the Numerical Rating Scale (NRS; 0-10) at predefined postoperative time points, including before and after rescue analgesic administration.
Morphine Exposure and Relationship With Rescue Analgesic Hazard
Relationship between predicted morphine plasma concentration derived from individual dosing histories and the hazard of subsequent rescue analgesic administration.
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