The QT interval is a measure of the combination of cardiac depolarization and repolarization as it encompasses both the QRS complex and the J-T interval. QT, QTc, QTd prolongation or shortening has been associated with ventricular arrhythmias . In order to define non-torsogenic drug-induced arrhythmias, the index of cardio-electrophysiological balance (iCEB), which is a new marker calculated with the QT/QRS formula, has been defined. In our study, we planned to evaluate the effects of dexmedetomidine and propofol on cardiac electrophysiology with all these parameters, especially the newly defined iCEB.

Seventy patients who underwent operation under regional anesthesia and received intraoperative sedation will be included in the study. The patients will be divided into two groups, Group D (dexmedetomidine) and Group P (propofol). Sedative agent infusion will be started immediately after spinal anesthesia is administered. Preoperative ASA (American Society of Anesthesiologists) scores, demographic data, comorbidities and medications used will be recorded. Vitals and ECG prior to spinal anesthesia will be recorded. After that, spinal anesthesia will be applied and vitals and ECG will be recorded at 1, 5, 10, 15, 45 and 75 minutes. The sedation levels of the patients will be measured noninvasively by bispectral index (BIS) monitoring. Patients will be kept within the limits of light sedation. The maximum dose of 1.4 micrograms/kg/hour in the dexmedetomidine group (group D, n=35) and 4.5 milligrams/kg/hour in the propofol group (group P, n=35) will not be exceeded. The following parameters were set as the safety endpoint during sedation:

• Respiratory rate ≤8
• SpO2; 95
• Heart rate; 40
• Systolic blood pressure;80 At these endpoints, the patient's sedation dose will be reduced regardless of the BIS value.

During sedation, patients will be given 3 liters of nasal oxygen per minute, which can be increased according to need. Just before and 1st, 5th, 10th, 15th, 45th, 75th minutes after spinal anesthesia systolic arterial pressure, diastolic arterial pressure, mean arterial pressure,peak heart rate, oxygen saturation, bispectral index, QT time, QTc, QT distribution, Tpe, iCEB will be evaluated.

Inclusion Criteria:

• Patients with ASA Ⅰ-Ⅱ ,
• 18-80 years old, who will be operated under spinal anesthesia

Exclusion Criteria:

• Hypersensitivity to the propofol,dexmedotimidine
• preoperative QTc prolongation
• preoperative heart disease
• use of drugs that affect the QT interval
• severe sinus bradycardia
• preoperative electrolyte abnormalities
• liver and kidney function abnormalities
• non-sinus rhythm