Ketamine for Pain Relief in Bariatric Surgery

After obtaining approval from the hospital ethics committee and written informed consent from the patients, this prospective randomised study will be conducted on 76 patients belonging to ASA physical patients status II and III of either sex, scheduled to undergo laparoscopic bariatric surgery (sleeve gastrectomy, Roux-en-Y gastric bypass) under general anaesthesia. The patients will be randomly allocated by computer generated numbers to one of the following two groups of 38 patients each.

Group 1[Ketamine + Fentanyl Group, n=38]: Pre-induction fentanyl 1-mcg/kg, ketamine 0.5-mg/kg after induction, followed by intra-operative fentanyl infusion of 0.5-mcg/kg/hr + ketamine infusion of 0.2-mg/kg/hr

Group 2[Fentanyl Group, n=38]: Pre-induction fentanyl 1-mcg/kg, saline after induction followed by intra-operative fentanyl infusion of 0.5-mcg/kg/hr + saline infusion.

Both the groups will receive intravenous PCA of fentanyl post-operatively.

Randomisation, Allocation Concealment:

The patients will be randomly allocated to one of the two groups based on a computer-generated random number table (url:stattrek.com/statistics/random-number-generator.aspx). Randomisation sequence concealment will include opaque-sealed envelopes with alphabetic codes whose distribution will be in control of an independent analyst. The envelopes will be opened; patient's data-slip will be pasted on them, and will be sent back to the control analyst.

Blinding Strategy:

The attending anaesthesiologist will be blinded to the intra-operative infusions used. Postoperative patient recovery profile will also be evaluated by an independent assess or blinded to the intra-operative anaesthesia technique.

Management of Anaesthesia:

Premedication

All patients will be receive tablet ranitidine-150 mg night before and on morning of surgery.They will be instructed to fast for at least 8- hours before surgery. Clear fluids will be allowed till 2 hours before surgery.

Intra-operative Monitoring

Two peripheral venous lines (18G/20G catheter) will be secured. Standard monitoring including 5-lead ECG, non-invasive blood pressure (NIBP), pulse oximeter, end-tidal carbon dioxide (EtCO2) and end-tidal gas monitoring will be applied. Additional monitoring will include depth of anaesthesia monitoring using Bi-spectral index (BIS) and neuromuscular monitoring using train-of-four response.

Anaesthesia Technique

All patients will be pre-oxygenated with 100% oxygen for at least 3-minutes prior to induction of anaesthesia. All the drugs (study + control) will be administered based on lean body weight (LBW). Patients in the KF group will receive pre-induction fentanyl-citrate l-µg/kg IV and ketamine 0.5-mg/kg after induction whereas patients in the Fentanyl group will receive pre-induction fentanyl-citrate l-µg/kg IV and saline as in above group. Anaesthesia will be induced with propofol 2-2.5mg/kg titrated to a BIS-value of 50.. After induction of anaesthesia, atracurium besylate 0.5-mg/kg will be administered for skeletal muscle relaxation to facilitate tracheal intubation. Ventilator settings for CMV, tracheal tube size [7.5-mm I.D (male), 6.5-mm I.D (female)], and breathing circuit (circle-CO2 absorber system) will be the standardised in all the patients. The patients in the Ketamine + Fentanyl group will receive fentanyl infusion at 0.5-mcg/kg/hr and ketamine infusion of 0.2-mg/kg/hr. The patients in the Fentanyl group will receive fentanyl infusion at 0.5-mcg/kg/hr and saline infusion. The LBW in obesity patients scheduled to undergo bariatric surgery will be calculated based on the following formulae:

9270 x TBW (kg)/6680 + (216 x BMI) [men]

9270 x TBW (kg)/8780 + (244 x BMI) [women]

Desflurane in oxygen-nitruos oxide mixture (FiO2 0.50) will be used for maintenance in both the groups to maintain a BIS of 40-60. Intra-operative muscle relaxation will be maintained using atracurium boluses controlled by train-of-four response on peripheral neuromuscular monitor. Thirty minutes before the end of surgery, non-opioid analgesics, such as paracetamol 1-gm will be administered to the patient. Desflurane delivery will be stopped at the point of completion of skin closure. Residual neuromuscular blockade (assessed with train-of-four response) will be reversed with neostigmine (50-µg/kg) and glycopyrrolate (20-µg/kg).

After discontinuation of anaesthesia delivery (0-time point) the time to eye opening and time to extubation will be determined. After tracheal extubation the patients will be shifted to postoperative recovery room adjoining OT suites and will be closely observed for oxygenation and ventilation status, pain (visual analogue score [VAS]), sedation (Modified OASS), and PONV.

Intravenous Patient Controlled Analgesia (IV-PCA) pump containing fentanyl citrate-2.5 mcg/ml will be attached to all the patients upon shifting to the recovery room. The IV-PCA pump settings will be as follows: 0-ml basal dose; 4-ml PCA dose; 15-minutes lock out interval. A baseline visual analogue scoring will be done after shifting the patient to the recovery room (0-time point) followed by 2-hours, 4-hours, 8-hours, 12-hours, and 24-hours time points from the baseline. Any adverse effects such as hypotension/ hypertension, bradycardia/tachycardia, hypoxemia, giddiness will be recorded and treated. Post-surgery, time to alimentation post surgery will be noted.

'Rescue' pain relief drug will include: diclofenac sodium 75 mg slow IV bolus for NRS>3 and 'rescue' antiemesis agent would be ondansetron 4-mg for a PONV score > 1.