The purpose of this study is to evaluate the stroke volume variation measured by both methods: transpulmonary thermodilution and electrical impedance tomography (EIT), during fluid responsiveness maneuvers and after fluid replacement in the immediate postoperative of coronary artery bypass grafting (CABG) patients. Patients will be hemodinamically monitored with the VolumeView set in combination with EV1000 clinical platform and the display of valuable volumetric parameters (Edwards Lifesciences, California, USA). Simultaneoulsy, patients will be monitored with Enlight Electrical Impedance Tomography (Timpel, São Paulo, Brazil). Hemodynamic data will be assessed at baseline 1, one minute after the passive leg raising maneuver, after PEEP increment, and after 500 mL of Lactated Ringer's (bolus infusion). Blood gases sample will be assessed before and immediatly after the protocol.

In the ICU, immediately after CABG surgery, patients are submitted to mechanical ventilation (volume-controlled mode with tidal volume = 8mL/Kg of PBW, PEEP = 8cmH2O and FiO2 = 60%, respiratory rate to maintain PaCO2 = 35 - 45 mmHg); hemodynamically monitored with VolumeView set in combination with EV1000 clinical platform and the display of volumetric parameters (Edwards Lifesciences, California, USA). Electrical impedance tomography monitoring (Enlight, Timpel, São Paulo, Brazil) is performed with a pair of electrodes belt attached around the thorax at 4Th - 6Th intercostal space, and a flow sensor attached between the orotracheal tube and the Y connector from the ventilator.

Before initiate the protocol, patients are submitted to a bolus of usual care doses of sedation and muscular blockage (Fentanyl, Midazolam and Cisatracurium).

To assess fluid responsiveness patients will be submitted to two different maneuvers applied in a random way: Passive Leg Raising (PLR) ant PEEP increment (PEEP). And after these maneuvers patients will receive a bolus of 500 ml of Lactated Ringer's.

Measurements are performed one minute after each of these conditions:

• Baseline: before both fluid responsiveness maneuvers, before and after Lactated Ringer infusion, patient is positioned in 450 semi-recumbent position;
• PLR: Fluid responsiveness maneuver which patient is positioned from 450 semi-recumbent position to dorsal decubitus and the legs are raised at 450;
• PEEP increment: Fluid responsiveness maneuver which consisted in increased the PEEP level 5 cmH2O above the mean airway pressure, patient is positioned in 450 semi-recumbent position
• Infusion of 500 mL of Ringer's; 450 semi-recumbent position.

Transpulmonary Thermodilution assessment are performed by the injection of 3 cold salines in bolus - the injection volume varied from 10 - 20mL according to the patient's actual weight and EIT assessment are performed by 1 injection of 10 mL of hypertonic saline at 7.5 - 10% according to the patient's actual weight.

Inclusion Criteria:

• Elective CABG surgery
• Age greater than 18 years old and less than 80 years old
• Written inform consent

Exclusion Criteria:

• Previous pulmonary disease or pulmonary hypertension
• Previous renal replacement therapy
• Left ventricular ejection fraction < 40%
• Body mass index > 40 kg/m2
• Atrial fibrillation
• Presence of cardiac pacemaker or another implantable electronic device
• Bleeding associated to hemodynamic instability
• Cardiac arrest or suspicion of neurological alteration
• Hemodynamic instability (norepinephrine dose > 0.5 mcg/Kg/min)