Study Design: Prospective randomized double-blind controlled trial

Randomization and grouping of the patients:

Using computer generated random number table, 62 patients will be randomly allocated to receive one of the following interventions as per the group allocation:

-Intervention group (n=31) (Group D): patients will receive intravenous (IV) dexmedetomidine 1mcg/kg slowly over 10 minutes diluted to 50 ml with normal saline (NS) after induction of general anaesthesia to the patient and bilateral erector spinae plane block will be given 10 minutes after allocated intervention.

-Control group (n=31) (Group S): patient will receive 50 ml of intravenous saline as a control, over 10 minutes, after induction of general anaesthesia to the patient and bilateral erector spinae plane block will be given 10 minutes after allocated intervention.

Group allocation will be concealed in a coded opaque sealed envelopes. An investigator(not involved in the study) will open the envelope on the day of surgery and 1mcg/kg dexmedetomidine in 50 ml NS or only 50 ml NS will be given intravenously before performing the block according to allocation and decoding will be done at the end of the study. The drugs will be prepared in identical looking syringes labelled with a random number by a person not involved in the study.

Preparation of the patient:

Preoperatively a complete pre- anaesthetic evaluation and relevant investigation will be performed in all patients. They will be explained about the linear visual analog scale (VAS) for pain ( 0- no pain to 10- worst imaginable pain) in their own vernacular language. The patients will be educated about the use of intravenous patient control analgesia ( IV-PCA) pump regarding demand based requirement of analgesia. All the patients will be kept fasting for minimum 6 hours and premedicated with tablet ranitidine 150 mg and tablet alprazolam 0.25 mg orally on the night before surgery and 6 AM morning of surgery.

In the operating room patients will be connected to multichannel monitor (Aespire View GE Healthcare Helsinki, Finland) and monitoring for electrocardiogram (ECG), non-invasive arterial blood pressure (NIBP), oxygen saturation (SpO2), respiratory rate (RR) and end-tidal CO2 (EtCO2) will be done as per standard norms. All baseline parameters will be recorded and monitored continuously throughout the procedure. An intravenous infusion of 0.9% saline by 18G/20G peripheral venous cannula will be initiated. All patients will receive a standardized general anaesthesia which would include injection glycopyrrolate 2mcg kg-1,injection morphine 0.1mg kg-1 intravenously (IV). Preoxygenation with 100% oxygen would be done for 3 minutes. Intravenous induction would be achieved by injection propofol 2mg kg-1. After checking the ability to adequate mask ventilation injection vecuronium 0.1 mg kg-1 will be used to facilitate endotracheal intubation. After ensuring bilateral air entry endotracheal tube will be fixed. Anaesthesia will be maintained by N2O/O2 in a ratio of 60:40 with sevoflurane (inspired concentration of 1-2%).

Subsequently ultrasound guided ESP block will be given to the patients 10 minutesafter allocated intervention by an experienced investigator/anaesthesiologist as per the technique described later. Thereafter the surgery will be allowed to proceed. Intraoperatively, the rise in mean arterial blood pressure (20% above baseline) and surgical pleth index (SPI>50) for two consecutive readings will be treated with injection fentanyl 0.5 mcg/kg. Any additional requirement of intraoperative analgesia will be noted and the observations will be recorded in proforma.Hypotension or bradycardia encountered intraoperatively or in the recovery room will be treated according to the following algorithm: bradycardia (HR<60), 0.3-0.5mg IV atropine; hypotension (MAP decrease by 20% from baseline), 0.1 mg IV phenylephrine or/and 200ml fluid bolus. At the end of the surgery, the residual neuromuscular blockade will be antagonized with IV neostigmine 50 mcg kg-1 and glycopyrrolate 10 mcg kg-1. Patient will be extubated and shifted to post anaesthesia care unit. In post anaesthesia care unit (PACU), patients in both study groups will be connected to IV-PCA pump (Micrel Rythmicâ„¢ Evolution PCA) with morphine in the strength of 1mg ml-1 with a lockout interval of 5 minutes and the maximum dose of morphine being 0.2 mg kg-1 body weight over 4 hours. Patient will be asked to take a bolus if VAS score >3. Routine analgesia with paracetamol 1 gram IV 6 hourly and injection diclofenac 75mg IV 12 hourly will be given to both the groups.

Technique of ESP block

After induction of general anaesthesia, the patient will be placed in the prone position. Skin over the back will be prepared by 10% povidone iodine solution. After ensuring complete aseptic precautions and draping of the area a high frequency linear or curved array ultrasound probe(SonoSite Edge, Bothell, WA, USA) (depending upon BMI of the patient) covered with a sterile sleeve will be used. The ultrasound probe will be placed inlongitudinal parasagittal orientation 3 cm lateral to the midline of the vertebral column. The transverse processes of the vertebrae at the (mid) level of the surgery and the erector spinae muscle (ESM) will be identified. Depending on the depth a 8 or 10 cm 22 G ultrasound needle(Pajunk, Geisingen, Germany) will be inserted via in plane technique in a cephalad to caudal direction until bone contact with the tip of the transverse process (TP) is reached. After slight retraction of the needle, hydro dissection with 2 ml normal saline was done to confirm separation of ESM from TP. 20 ml 0.25% bupivacaine with adrenaline will be injected under vision in aliquots of 5 ml after negative aspiration . The drug spread was seen in the ESP plane craniocaudally. The same procedure will be repeated on the contralateral side.

Observations

An investigator blinded to the group allocation will record the observations intraoperatively and from postoperative recovery room to the ward. Patients will be monitored for non invasive blood pressure (NIBP), pulse rate (PR) , respiratory rate (RR) and these recordings will be noted at 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, 12 hours and 24 hours. Simultaneously, at these time intervals the pain will be evaluated by using VAS score which will be evaluated both at rest and on movement. Time to the first bolus (TFB) of morphine will be recorded in both the groups. Intraoperative fentanyl consumption and cumulative morphine consumption through IV PCA over 24 hours in post operative period will be calculated and compared in both the groups. The Ramsay Sedation score will be used to assess sedation ranging from being agitated to asleep with no response to tactile stimulation (1- Anxious or agitated, 2- Co-operative and tranquil, 3- Drowsy but responsive to command, 4- Asleep but responsive to glabellar tap, 5- Asleep with a sluggish response to tactile stimulation, 6- Asleep and no response). The score will be evaluated every hourly till the requirement of first dose of morphine bolus. Excessive sedation will be defined as a sedation score of more than 4 (i.e. 5or 6). Overall patients satisfaction with analgesia will be evaluated on the first postoperative day by using a 4-point verbal score which ranged from very dissatisfied up to very satisfied (1- very dissatisfied; 2- dissatisfied; 3- satisfied; 4- very satisfied). Any additional requirement of analgesia will be observed and noted.All the observations including demographic data, VAS, RSS, intraoperative analgesic requirement and total analgesic requirements will be recorded along with any side effect related to the procedure/drug over 24 hours post operativelyin the prescribed proforma. Decoding will be done at the end of the study and the data will be analysed using appropriate statistical tests.

Primary outcome will be cumulative morphine consumption over first 24 postoperative hours. Secondary outcomes will be VAS scores, Ramsay sedation score, time to first bolus of morphine, satisfaction scores, side effects of intravenous dexmedetomidine/procedure.