How can mechanical ventilation cause atelectasis (collapse of lung tissue)?

From the Guidelines

Mechanical ventilation can cause atelectasis through several mechanisms, including compression atelectasis, oxygen toxicity, and inadequate positive end-expiratory pressure (PEEP), and to minimize this, strategies such as using appropriate PEEP levels and implementing lung recruitment maneuvers are recommended. Mechanical ventilation can lead to compression atelectasis by pushing the diaphragm upward and compressing the dependent lung regions 1. Oxygen toxicity is another factor, as high concentrations of oxygen can displace nitrogen in alveoli, leading to absorption atelectasis when the oxygen is absorbed into the bloodstream faster than it can be replaced. Ventilator settings that don't provide adequate PEEP can allow alveoli to collapse during exhalation, as found in studies where zero end-expiratory pressure (ZEEP) was used, resulting in a reduction in end-expiratory lung volume (EELV) and an increased area of atelectasis 1. Some key points to consider in lung-protective ventilation include:

• Low tidal ventilation (6-8 ml kg-1) and PEEP (5 cm H2O) should be used initially 1
• Alveolar recruitment maneuvers are beneficial in reopening collapsed alveoli and improving lung mechanics 1
• High ventilator driving pressure has been recognized as a significant determinant of lung injury and is linked to postoperative pulmonary complications (PPCs) 1 Additionally, mechanical ventilation often requires sedation and sometimes paralysis, which reduces normal sighing and deep breathing patterns that naturally prevent atelectasis. Mucus plugging can also occur due to impaired mucociliary clearance in intubated patients, blocking airways and causing distal collapse. To minimize ventilator-induced atelectasis, strategies include:
• Using appropriate PEEP levels (typically 5-10 cmH2O) 1
• Implementing lung recruitment maneuvers 1
• Avoiding unnecessarily high oxygen concentrations
• Positioning patients properly (often prone positioning)
• Ensuring adequate humidification of inspired gases to prevent mucus plugging 1

From the Research

Mechanical Ventilation and Atelectasis

Mechanical ventilation can cause atelectasis due to several factors, including:

• Inadequate positive end-expiratory pressure (PEEP) settings, which can lead to lung collapse and atelectasis 2, 3, 4
• Lack of recruitment maneuvers, which can help to open up collapsed lung tissue and improve lung volumes 5, 2, 3
• Use of low tidal volumes without proper PEEP settings, which can lead to atelectasis and decreased oxygenation 2, 3

Importance of PEEP Settings

PEEP settings play a crucial role in preventing atelectasis during mechanical ventilation. Studies have shown that:

• Individualized PEEP settings can improve lung volumes, oxygenation, and reduce atelectasis 3
• Higher PEEP levels may be necessary to keep the lungs open and assure homogeneous ventilation, especially in patients with acute respiratory distress syndrome (ARDS) 6
• Low PEEP levels without recruitment maneuvers can lead to increased atelectasis and decreased oxygenation 2, 4

Recruitment Maneuvers

Recruitment maneuvers can help to open up collapsed lung tissue and improve lung volumes. Studies have shown that:

• Recruitment maneuvers followed by titrated PEEP can improve lung volumes, oxygenation, and reduce atelectasis 5, 2, 3
• Recruitment maneuvers may not be necessary in all cases, and PEEP alone may be sufficient to minimize atelectasis in healthy lungs 4