The goal of this observational study is to learn about the intraoperative and postoperative pulmonary effects of tidal volume adjustment according to force vital capacity in thoracic surgery patients. The main question it aims to answer is:

Is there any positive effect of tidal volume adjustment according to force vital capacity on intraoperative and postoperative lung function in thoracic surgery patients?

Participants already taking tidal volume adjustment according to force vital capacity or predicted body weight during toracic surgery. As part of the medical care of thoracic surgery patients, intraoperative hemodynamic variables, lung dynamics and blood gas values and postoperative pulmonary complications will be monitored.

Patients over 18 years of age and American Society of Anesthesiologists (ASA) physical status I-III who scheduled for elective thoracic surgery under general anesthesia will be included. Exclusion criteria: age > 18 years old, ASA I-III; III, pregnancy, presence of large bullae and/or pneumothorax, previous lung resection surgery, intensive care unit (ICU) admission in the preoperative period, predictive postoperative ICU admission, pneumonectomy surgery, and missing data.

In the operating room, all patients will be monitored with electrocardiogram, pulse oximeter, non-invasive arterial blood pressure. Anesthesia management, intraoperative and postoperative fluid management, postoperative analgesia regimens were will be standard procedures at the clinic for all patients.

During two-lung ventilation (TLV), mechanical ventilation will be set for a tidal volume (TV) of 7 ml/predicted body weight (PBW) for Group I, FVC/8 ml for Group II. Other settings will be similar between two groups; respiratory rate of 10-14 breaths/min, inspiratory time (Ti) of 33% without inspiratory pause.

Demographic data, functional status, ARISCAT score, hemodynamic values, respiratory measurements (peripheral oxygen saturation: SpO2, Ppeak, Pplato, TV, lung compliances, FiO2, end-tidal carbon dioxide: EtCO2), blood gas analysis (PaO2, PaCO2), and PaO2/ FiO2 rate will be recorded after intubation on TLV (T1), after lateral position on TLV (T2), after 30 min onset OLV (T3), the end of OLV on TLV (T4), and before extubation on TLV (T5).

Duration of anesthesia, duration of OLV, urine output, estimated blood loss, fluid therapy (ml, crystalloid and colloid), the need for blood product (ml), intraoperative complications, and the need for inotrope or vasopressor agent will also recorded during surgery.

The patients will be visited during postoperative five days (day 1: postoperative first day) and respiratory complications (pneumonia, pneumothorax, additional oxygen therapy, respiratory failure, acute respiratory distress syndrome, unplanned invasive or noninvasive mechanical ventilation, prolonged air leak, pleural effusion, atelectasis, cardiopulmonary edema) will be evaluated and recorded daily.

Length of hospital stay and in-hospital mortality will be also recorded. Hospitalization or intensive care unit admission within 30 days after surgery and mortality at 28 days will be assessed by calling the patients and their relatives by phone.

Inclusion Criteria:

• Patients over 18 years of age
• American Society of Anesthesiologists (ASA) physical status I-III
• Scheduled for elective thoracic surgery under general anesthesia

Exclusion Criteria:

• Age over 18 years old,
• ASA > III,
• Pregnancy,
• Presence of large bullae and/or pneumothorax,
• Previous lung resection surgery,
• Intensive care unit (ICU) admission in the preoperative period,
• Predictive postoperative ICU admission,
• Pneumonectomy surgery

patients scheduled for elective thoracic surgery under general anesthesia