To meet the unmet need of better and safer pain relief for acute pain in the post-operative setting, a Vital-signs-integrated Patient-assisted Intravenous opioid Analgesia ("VPIA") Delivery System, with novel and intelligent software algorithms and specialised hardware was developed. In the previous project, the investigators have shown that this system has the potential to increase the safety and patient satisfaction with intravenous opioid analgesia. However, opportunities to develop more robust vital signs monitoring with the goal of ensuring continual and effective analgesia are identified.

The primary aim of this proposal is to advance the development of technology (through new features and functionality) and perform clinical evaluation of the VPIA system with a larger sample size to show improvements in patient's satisfaction (pain relief) and robustness of system in terms of vital signs integration. Novel technology using adaptive vital signs controller, integrated with an infusion pump and single finger probe vital signs monitor system will be developed with the aim for commercialisation.

The investigators will conduct a prospective cohort study in 150 adult female subjects that undergo major surgery that require postoperative patient controlled morphine analgesia so as to examine the monitoring performance of oxygen desaturation, respiratory depression and patient satisfaction and user feedback.

Patients who are undergoing elective surgery with plan to use postoperative patient controlled analgesia with morphine will receive study information either at pre-operative assessment clinic or upon admission for surgery if they have not attended the pre-operative assessment clinic. They will be screened for eligibility using the inclusion and exclusion criteria. If eligible for recruitment, the patients will be approached by the investigators for recruitment. Upon successful recruitment of the study, patients will be asked to complete two questionnaires and rate their pre-surgical pain on the numerical rating scale in the pre-anaesthetic evaluation clinic. The general anaesthesia technique and type of analgesia administered intra-operatively will be according to standard practice and is at the discretion of the attending anaesthesiologist. After surgery, patients will be reviewed daily (up to 3 days) in the post-operative wards. They will be asked on questionnaire scoring, pain score, and analgesia information and adverse event, if any.

Inclusion Criteria:

• American Society of Anaesthesiologist (ASA) physical status I-III;
• Age 21-70 years;
• Receiving patient controlled analgesia of morphine for postoperative analgesia.

Exclusion Criteria:

• Allergy to study drug;
• With significant respiratory disease and obstructive sleep apnea;
• Unwilling to place oxygen saturation and respiratory rate monitoring during study period;
• Unable to comprehend the use of patient controlled analgesia;
• Obstetric patients.

Only females undergoing gynecologic surgery in KKH will be recruited.