Opioid Free Anesthesia in Obese Patients.

Patients will be randomly allocated (by closed envelope method) to two groups:

Group A (n=38) will have opioid free anesthesia (OFA) Group B (n=38) will have opioid based anesthesia (OPA) All patients will be subjected to a preoperative clinical examination and routine preoperative laboratory investigations. Patients also will be trained on how to deal with the VAS score before surgery. The visual analog scale (VAS) is a pain score using a 10-cm line with two ends "no pain" on the left end and the "worst pain" on the right end, used to track pain for a patient or to compare pain between patients.(9,10) In the operating room (OR), peripheral oxygen saturation (spo2), noninvasive blood pressure and electrocardiogram ( ECG) will be monitored and recorded as a baseline reading. A peripheral intravenous cannula will be inserted t hen patients in both groups will receive 1mg of midazolam prior induction of anesthesia. Preoxygenation 3-5 minutes before induction will be done. Group (A): Induction of general anesthesia will be done using lidocaine (1.5 mg/kg), propofol (2-3 mg/kg), and atracurium (0.5 mg/kg). Dexmedetomidine 0.5 µg/kg over 10 min, started 10 min before induction. Following tracheal intubation, dexmedetomidine infusion generally will be initiated at 0.6 μg/kg/h and titrated between 0.2 and 1.0 μg/kg/h according to the heart rate maintaining bispectral index (BIS) between 40-60, lidocaine (1.5 mg/kg/h). ketamine will be given as a bolus dose of 0.3 mg/kg after induction and prior to skin incision then 0.2 mg/kg/h as an infusion. Patients will receive dexamethasone (8 mg i.v.) after induction. In group (B) for induction of anesthesia, patients will receive propofol 2-3mg/kg, fentanyl 1-2mcg/kg and atracurium 0.5 mg/kg as a muscle relaxant to facilitate intubation. Fentanyl bolus doses of 0.5-1 mcg/kg will be given to keep BIS score 40-60 during surgery.

All Patients will be mechanically ventilated with 50% O2 and 50% air and the end-tidal carbon dioxide( CO2) will be maintained between 30 - 35 mmHg. Anesthesia will be maintained by isoflurane and atracurium 0.1-0.2 mg/kg every 20-30 minutes. Reversal of muscle relaxants will done by using intravenous neostigmine (0.05 mg/kg) and atropine (0.01 mg/kg) at the end of surgery and the patient will be extubated when the patient will be able to breath spontaneously with tidal volume ≥5ml/kg and spo2>92%. Paracetamol 1gm i.v. infusion and ketorolac 30 mg slow i.v injection will be used at the end of surgery and before emergence in both groups. At the recovery room, patients will assess their pain and rating it using VAS score, monitored for postoperative pain, the patients will leave the post anesthesia care unit (PACU) with Aldrete score more than 9. (11) Any patient with Vas score ≥4, will receive tramadol 1mg/kg i.v. with a maximum dose 600mg/day.

Inclusion criteria

• American Society of Anesthesiologist (ASA) physical status Ⅱ , Ⅲ.
• body mass index (BMI) ≥30 kg/m2.
• Have upper limb surgeries (orthopedics, plastic,…) under general anesthesia.

Exclusion criteria

• Known allergy to the drugs will be used in the study.
• Pregnancy and lactation.
• Addiction or recent use of opioids'
• Patients will not be able deal with visual analog score(VAS).
• Hepatic, Renal and cardiac diseases in advanced stages.
• History of epilepsy or seizures.
• Patients with cerebrovascular disease.