The Effect of Intraoperative Dexmedetomidine on Renal Function After Coronary Artery Bypass Graft Surgery

This study will include patients admitted to the Clinic for Cardiovascular Surgery of the Institute of Cardiovascular Diseases of Vojvodina, planned for elective coronary artery bypass graft surgery (CABG). Basic demographic and anthropometric data (gender, age, height, weight, and body mass index) and data on comorbidities, therapy, and allergies will be recorded. The day before surgery, all patients will undergo transthoracic echocardiography, on the basis of which the ejection fraction of the left ventricle will be determined and recorded. After the entire examination, the New York Heart Association (NYHA) class, American Society of Anaesthesiologists physical status (ASA score), and Estimate risk of in-hospital death after cardiac surgery score (EuroSCORE II) will be determined. The method and purpose of the research will be explained to all patients, after which informed consent for participation in the research will be obtained.

The patients will be divided into two groups (experimental and control) using the randomization method. All patients will have blood drawn for laboratory and biochemical analyses the morning before surgery: urea, creatinine, cystatin C, IL-6, hemoglobin, leukocytes, platelets, glycemia, aspartate aminotransferase (AST), alanine transaminase (ALT), lactate dehydrogenase (LDH), direct and total bilirubin, fibrinogen, CRP, CK-MB, hS troponin I, electrolytes (Na+ and K+), and lactates. With the help of the Cockcroft-Gault formula, the estimated glomerular filtration rate (eGFR) and creatinine clearance (CCr) will be determined. The values of all these analyses will be defined as basal values.

The anesthetic and surgical protocol, as well as the postoperative treatment, will be standardized. Half an hour before arriving in the operating room, patients will receive about 0.05 mg/kg of midazolam per os as premedication. Upon arrival in the operating room, electrodes for continuous monitoring of the electrocardiogram (ECG), electrodes for assessing the depth of anesthesia, and pulse oximetry for monitoring pulse saturation (SpO2) will be attached to all patients. Anesthetist nurses will place a peripheral venous cannula, usually in one of the veins of the right arm, through which infusion solutions will be applied in the perioperative period and if necessary, transfusions of autologous blood, resuspended erythrocytes, platelets, and fresh frozen plasma. The anesthesiologist will place the arterial cannula, mostly in the left radial artery, for continuous monitoring of arterial blood pressure values. After adequate preoxygenation (8 l/min, 3 min) via a ventilation mask, the intravenous anesthesia will be administered with a combination of the benzodiazepine midazolam (about 0.05 mg/kg), the opioid analgesic sufentanil (about 0.15 µg/kg), intravenous anesthetic propofol (about 1 mg/kg), and the neuromuscular relaxant rocuronium bromide (about 0.8 mg/kg). After endotracheal intubation, patients will be on mechanical lung ventilation (MLV) - volume-controlled ventilation mode with a tidal volume of 6-8 ml/kg of ideal body weight, a respiratory rate of 12/min, FiO2 of 0.5, a positive end-expiratory pressure (PEEP) of 5 cmH2O, and an inspiratory ratio to expirium - I:E 1:2. The flow of fresh gases at the MLV in all patients will be 3 l/min. Correction of MLV parameters will be done based on partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2) in arterial blood, with the aim of maintaining PaO2 >100 mmHg and PaCO2 35-45 mmHg. A three-lumen central venous catheter (CVC) will be placed mainly in the right interior jugular vein. All patients will be placed with a urinary catheter to monitor hourly diuresis as well as a nasopharyngeal probe to monitor nasopharyngeal temperature.

Dexmedetomidine solution will be prepared by diluting one ampoule of dexmedetomidine (200µg/2ml) with 48 ml of saline solution to obtain a dexmedetomidine solution of 4µg/ml. Patients from the experimental group will receive a continuous infusion of dexmedetomidine at a dose of 0.5 µg/kg/h, until the end of the operation. Patients in the control group will receive the same volume of saline solution.

Anesthesia will be maintained with the inhaled anesthetic sevoflurane, with target depth of anesthesia values between 40 and 60, as measured by entropy. A continuous intravenous infusion of sufentanil (0.5-1 µg/kg/h) will be used for intraoperative analgesia. Neuromuscular relaxation will be maintained by intermittent bolus doses of rocuronium bromide (on average, about 0.4 mg/kg/h). All patients will receive an intravenous antibiotic (Ceftriaxone 1g) half an hour before the surgical incision, and in cases of allergy to cephalosporins, Vancomycin 500 mg. All patients are prescribed tranexamic acid according to the protocol.