Effectiveness of Peripheral Dexmedetomidine for Bilateral Third Molar Surgery Under General Anaesthesia

The study protocol was approved by our local Institutional Review Board and written consent was obtained from all the participants. Eligibility for recruitment included American Society of Anesthesiologists (ASA) physical status I and II, age between 18 and 50 years of age with 4 bilateral impacted third molar teeth scheduled for extraction under general anaesthesia. Exclusion criteria included clinical history or electrocardiographic evidence of heart block, ischaemic heart disease, asthma, sleep apnoea syndrome, impaired liver or renal function, alcohol consumption in excess of 28 units per week, pregnancy, patient refusal, known psychiatric illness, chronic sedative or analgesic use, and regular use of or known allergy to dexmedetomidine, paracetamol or dextropropoxypheneopioids. Patients with preoperative inflammation at the site of surgery were also excluded.

After obtaining written, informed consent, patients were randomly allocated to receive 1)Preoperative IV dexmedetomidine 1mcg/kg and normal saline infiltrated to wound at the end of surgery; 2) Preoperative normal saline IV infusion and dexmedetomidine 1mcg/kg infiltrated to wound or 3) Preoperative IV normal saline infusion and normal saline infiltrated to wound at the end of surgery. A computer generated random sequence was used for drug allocation and this was prepared by a statistician who was unaware of the clinical nature of the study. The patients were assessed by the list anaesthetist the day before surgery. They were fasted for at least 6 hours and did not receive any premedication before arrival at the operation theatre. Patients were educated on the use of the Numerical Rating Scale (NRS) for pain assessment, where zero corresponds to no pain and 10 represents the worst pain imaginable.

A P-deletion test was performed in the ward preoperatively. The P-deletionThis test consists of 58 lines of closely typed text containing between 74 to 97 occurrences of the letter "p". The patients are instructed to cross out every letter "p" they can find as quickly as possible, reading from left to right down the page. The number deleted in 180 seconds and the number of errors counts. This test assesses speed, accuracy, concentration, mental activity, hand-eye coordination and vigilance. It was firstly described by Dixon and colleagues who found it to be an accurate test for psychomotor recovery from anesthesia and sedation (Dixon et al., 1973).

On arrival at the operating theatre, a 20-gauge intravenous cannula was inserted in the dorsum of each patient's left hand. Either dexmedetomidine 1 µg/kg (Group D) diluted to 4ml with normal saline or the same volume of 0.9% saline alone (Group P) was prepared by another anaesthetist who did not participate in patient management or data collection. Both preparations were clear solutions, therefore patients, medical, nursing staff, and data collectors were all blinded to the allocated drug. Heart rate, blood pressure, respiratory rate and oxygen saturation were recorded (S/5 Anesthesia Monitor, Datex-Ohmeda, WI, USA) before general anaesthesia and thereafter at five-minute intervals from the time of commencing surgery until discharge from the recovery room.

Induction and maintenance of anaesthesia were done according to a standard protocol. Anaesthesia was induced with propofol titration of 2 to 3 mg/kg, fentanyl 1 µg/kg and muscle relaxation was achieved with rocuronium 1 mg/kg. The trachea was intubated via the nasal route. General anaesthesia was maintained with a mixture of air, oxygen and sevoflurane at 1 to 1.5 MAC. Before the start of the surgical procedures, regional anaesthesia were performed by infiltrating 2.7 mL of 2% lignocaine with 1 in 80,000 adrenaline around the base of the gum of each third molar by the same team of dental surgeons. Sevoflurane was stopped when the last suture had been inserted. andVolume of 1 ml of either dexmedetomidine (Group D, totally dexmedetomidine 1 µg/kg for 4 surgical sites) or saline (Group P) was infiltrated to the submucosa of each surgical site. Neuromuscular block was antagonized with neostigmine 50 µg/kg and atropine 20 µg/kg, and followed by extubation after recovery of consciousness. The patients were then monitored in the recovery room for at least 30 minutes. Resting pain scores, blood pressure, heart rate, oxygen saturation and the Ramsay sedation score (RSS) (appendix 1) were assessed and recorded every 5 minutes. Intravenous ketorolac or morphine would be administered upon patients' request. Patients were transferred back to the general ward when fully consciousness with normal physiological parameters.