Although imaging techniques are the reference standard to diagnose alveolar collapse, in the postoperative period and using the peripheral hemoglobin oxygen saturation (SpO2), a non-invasive simple and accurate test (Air-Test) was recently validated to diagnose alveolar collapse.

The aim of this study is to non-invasively describe the incidence of intraoperative atelectasis with the Air-Test in an unselected surgical population. In addition, we attempt to describe the association between positive Air-Test and the patient´s preoperative or intraoperative variables.

Inclusion Criteria:

• American Society of Anesthesiologist (ASA) I-IV
• General Anesthesia
• Mechanical ventilation

Exclusion Criteria:

• age < 18 years old
• pregnancy
• patients undergoing cardiothoracic surgery
• ASA physical status V

The study included consecutive patients who were scheduled for surgery with general anesthesia and mechanical ventilation