This was a double-blinded prospective randomised study conducted in Universiti Kebangsaan Malaysia Medical Centre from January 2020 till November 2020. This study was approved by Dissertation Committee of the Department of Anaesthesiology and Intensive Care, Universiti Kebangsaan Malaysia Medical Centre (UKMMC) and Medical Research and Ethics Committee of UKMMC.
Consent was taken during preoperative visit whereby patients were counselled on the use of PCA machine and assessment of pain score using visual analogue scale (VAS). All patients were not given sedative premedication before surgery. Induction of general anaesthesia was with IV fentanyl 2 mcg/kg, IV propofol 2 mg/kg and paralysed with IV rocuronium 0.6 mg/kg. Patients were given IV dexamethasone 0.2 mg/kg for postoperative nausea and vomiting (PONV) prophylaxis. Anaesthesia was maintained with sevoflurane to achieve MAC of 1.0 with oxygen and air in 1:1 ratio. All patients received IV morphine 0.1mg/kg intraoperatively, and surgical site infiltrated with levobupivacaine 0.5% 2 mg/kg. IV granisetron 1 mg was given to all patients at the end of the surgery and reversal was with IV neostigmine 0.05 mg/kg and IV atropine 0.02 mg/kg.
All patients were connected to the PCA morphine with test drugs after arrival in the recovery area. Patients were encouraged to self-administer the PCA whenever required. In an event of uncontrolled pain, rescue analgesia was with IV fentanyl 20 mcg boluses. All patients upon discharged to ward from recovery bay must have pain score (VAS) of less than 4, respiratory rate more than 10, MAP \> 65 mmHg and HR \> 60 beats/minute.
Patients were followed up at 6, 12, and 24 hours after surgery to look at the cumulative PCA morphine usage, incidence of nausea and vomiting, sedation score, respiratory depression (respiratory rate \< 10 breath/min/). Side effects from dexmedetomidine namely hypotension (MAP \< 65) and bradycardia (HR \< 60) were also documented. The severity of nausea and vomiting was defined as mild, moderate, or severe while sedation was assessed according to five levels: 0, 1, 2, 3 and 4.
The power calculation for this study was based on a pilot study observing PCA consumption in the first 24 hours after surgery, with a mean difference, 14.67 and pooled standard deviation 20.27 in regard to dosage delivered comparing PCA morphine with dexmedetomidine 1 mcg/ml to PCA morphine with dexmedetomidine 2 mcg/ml. A group of 34 subjects each would be needed for a study with an alpha level of 0.05 (two-tailed) and a beta level of 0.2 (80% power) including 10% dropout rate.
Data were analysed using IBMR SPSSRs Statistics MacOS version 26.0 (IBM Corporation, New York, United States of America). The results were presented as frequency (percentage) and standard deviation whenever appropriate. The cumulative PCA morphine and dexmedetomidine usage pain score was analysed using the Mann-Whitney U-test. The incidence of sedation and PONV was analysed using Chi-square. Heart rate and blood pressure were analysed using independent T-test. A probability level of \< 0.05 was considered to be statistically significant.
