Optimal PEEP Level for Minimizing the Risk of Postoperative Atelectasis: A Retrospective Cohort Study Based on Lung Ultrasound Monitoring

Background: After surgery with general anesthesia, it is common for parts of the lungs to collapse, a condition called atelectasis. This can lead to low blood oxygen levels and other lung complications. Doctors use a setting on the breathing machine called PEEP (Positive End-Expiratory Pressure) to help keep the lungs open, but the best level to use is still debated. Purpose of the Study: The goal of this research is to find a PEEP level that minimizes the risk of lung collapse and low oxygen levels after surgery. The investigators will use lung ultrasound, a safe and non-invasive imaging method, to check the health of the lungs at the patient's bedside. The investigators will not assign treatments; they will observe the outcomes based on the PEEP level chosen by the patient's anesthesiologist during routine care. A simplified ultrasound scan will be used to score the amount of lung collapse before and after surgery. The main outcomes will be the frequency of lung collapse and the frequency of low oxygen levels (defined as SpO₂ of 90% or less).