Passive Leg Raising Test to Predict Hypotension During Induction of Anesthesia in Patients Undergoing Cardiac Surgery

In this randomized controlled clinical trial, the investigators hypothesized that passive leg raising induced changes in hemodynamic parameters could predict the hypotension during anesthesia induction. To evaluate this, before anesthesia, the investigators will conduct passive leg raising test. At first, the patient's trunk was elevated 45 degrees for the first set of measurements. Then, the lower limbs were raised to a 45° angle while the patient's trunk was lowered to a supine position to measure peak CO (usually within 1-2 min). Hemodynamic profiles planned to be measured are mean arterial pressure, heart rate, cardiac index, stoke volume and stroke volume variation. After this, the occurrence of hypotension (systolic blood pressure < 90mmHg or mean arterial pressure decrease > 30% of baseline) will be recorded during the time from anesthesia induction to surgical skin incision. Hypotension will be treated by a standardized method. If heart rate (HR) is less than 70 beats/min, 5mg of ephedrine will be administered and if HR is greater than 70 beats/min, 30 mcg of phenylephrine will be administered. This will repeated until hypotension subsided. Refractory hypotension will be defined as continuous hypotension despite the total infused dose of ephedrine > 0.5 mg/kg or phenylephrine > 4 mcg/kg. The ability to predict hypotension and refractory hypotension during anesthesia induction by passive leg raising test will be evaluated by receiver operating characteristic curve analysis.