Electrical Impedance Tomography Based Regional Lung Ventilation Evaluation According to Ventilation Strategy During Cardiopulmonary Bypass in Minimally Invasive Cardiac Surgery

Minimally invasive cardiac surgery (MICS) is a safe and effective surgical method that reduces bleeding, number of reoperations, postoperative pain, and length of stay in the ICU, and promotes faster recovery compared to conventional open thoracic cardiac surgery. In general, since cardiopulmonary bypass (CPB) is used during minimally invasive cardiac surgery using right thoracotomy, both lungs can be maintained in a lung rest state. Except for 2-3 ventilations when releasing the aortic forceps during surgery, there is no ventilation at all during CPB, and both lung ventilation starts when CPB is stopped. In order to secure the surgical field of view during surgery, most anesthetists do not ventilate the right lung and maintain a collapsed state. Even during CPB, ventilation can be performed without affecting the field of vision at the surgical site. However, to date, it is not well known about the proper ventilation method for the left lung during cardiac surgery using CPB.

Pulmonary complications are major postoperative complications of minimally invasive cardiac surgery and are factors that increase postoperative pulmonary complications, such as age, preoperative lung disease, and duration of CPB, which are well-known. Failure to ventilate the entire lung field at the time of CPB may cause atelectrauma, and even if normal ventilation is performed after CPB, and shearing force from repeated collapse and expansion of the atelectasis area may occur. In addition, such atelectasis can lead to not only ventilation disorders, ventilation/perfusion imbalances, but also postoperative pneumonia and poor prognosis. In particular, since right thoracotomy is mainly performed in minimally invasive cardiac surgery, the right lung collapses through one lung ventilation from the start of the operation to the access to the surgical site or at the end of the operation to check for bleeding at the surgical site. Therefore, one lung ventilation may be required even after weaning from the CPB, which may increase the risk of atelectasis in the operated side. Depending on the ventilation of the left lung during surgery and the tidal volume (TV), it may affect postoperative atelectasis and may cause functional ventilation. This can lead to the occurrence of respiratory complications such as pneumonia after surgery, resulting in poor prognosis.