Positive End-expiratory Pressure and Postoperative Atelectasis: A Randomized Controlled Trial

Area of Science:

• Anesthesiology
• Respiratory Physiology

Background:

• Positive end-expiratory pressure (PEEP) maintains lung volume and prevents alveolar collapse during anesthesia.
• Emergence from anesthesia with preoxygenation can lead to alveolar collapse due to gas absorption, particularly in dependent lung regions.

Purpose of the Study:

• To investigate if withdrawing PEEP before emergence preoxygenation reduces postoperative atelectasis.
• To assess the impact of PEEP withdrawal on lung atelectasis and oxygenation during emergence from general anesthesia.

Main Methods:

• A randomized controlled trial involving 30 patients undergoing nonabdominal surgery under general anesthesia.
• Patients received PEEP (7 or 9 cm H2O) during mechanical ventilation and were then randomized to either maintained PEEP or zero PEEP during emergence preoxygenation.
• Computed tomography (CT) scans assessed atelectasis at the end of surgery and 30 minutes post-extubation. Arterial blood gases measured oxygenation.

Main Results:

• No statistically significant difference in the increase of atelectasis area between the maintained PEEP group (1.6 cm²) and the zero PEEP group (2.3 cm²).
• Overall postoperative atelectasis was small, averaging 2.5% of total lung area.
• Postoperative oxygenation remained unchanged in both groups compared to the preoperative awake state.

Conclusions:

• Withdrawing PEEP before emergence preoxygenation does not limit postoperative atelectasis formation after nonabdominal surgery.
• Postoperative atelectasis is minimal and does not impact oxygenation, potentially due to the "open lung" achieved by intraoperative PEEP.