Pulmonary complications after cardiac surgeries are common. It is one of the most crucial concerns of cardiac surgeons and anesthesiologists. These adverse events may vary from a mild respiratory dysfunction to acute respiratory distress syndrome (ARDS). One of the most public reasons of these complications is atelectasis that would result in hypoxia and pneumonia. Any of these adverse events rises the prevalence of morbidity and mortality. The chief inducing causes for atelectasis are CPB and dropped blood perfusion and ventilation of the lungs. The ventilation arrest is related with a high frequency of retained bronchial sections, local atelectasis, decrease in arterial O2 concentrations as a effect of surge in arteriovenous shunt, declined lung compliance, pulmonary edema and hence increased risk of nosocomial infections.

Electrical Impedance Tomography (EIT) is a non-invasive, radiation-free, real time bedside imaging modality, which provide the assessment of regional gas volume and lung ventilation. EIT has been experienced in quite a lot of animal and clinical applications including optimization of mechanical ventilator strategies and recognition of respiratory adverse events. Besides, EIT has been used to recognize ideal PEEP by detection of homogenous ventilation in non-dependent and dependent lung regions. Homogeneous ventilation is key for inhibition of ventilator-induced lung injury.

The aim of this study is to use four different ventilatory strategies 【Group R : IMV(intermittent mandatory ventilation) Regular Ventilation with Tidal volume with 7ml/ kg (Predicted body weight) ； Group RP, Regular Ventilation with Tidal volume with 7ml/ kg (Predicted body weight) + PEEP : 6 cm H2O ；Group RI : Regular Ventilation with Tidal volume with 7ml/ kg (Predicted body weight) + Reverse IE ratio ventilation( I:E=1:1) ；Group RPI: Regular Ventilation with Tidal volume with 7ml/ kg (Predicted body weight) + PEEP : 6 cm H2O + Reverse IE ratio ventilation( I:E=1:1)】 to compare the beneficial in decreasing the incidence of post-operative pulmonary dysfunction after cardiac surgery including of the data of EIT, GAS , Lactate , PFR：PaO2/FiO2 ratio , cardiac index (CI) , BMI..etc . EIT were measured at two perioperative timepoints 1. after intubation at the onset of anesthesia with mechanical ventilation with 7ml/ kg (Predicted body weight) 2. at the end of surgery.

Inclusion Criteria:

• Age between 20-80 year-old
• Adult patients receiving elective cardiac surgery with hypothermic CPB

Exclusion Criteria:

• Patients were excluded if they had complicating comorbidities, such as chronic hepatic or renal insufficiency, acute cardiopulmonary failure requiring mechanical ventilation, intra-aortic balloon pump, or extracorporeal membrane oxygenation

De-identify the data before analyse the data by outcome saaessor