From the Guidelines
Mechanical ventilation can cause atelectasis through several mechanisms, including compression atelectasis, oxygen toxicity, inadequate positive end-expiratory pressure (PEEP), ventilator-associated lung injury, and sedation or paralysis, and to minimize this, clinicians should use lung-protective ventilation strategies with appropriate PEEP levels, typically 5-10 cmH2O, as recommended by recent studies 1.
Mechanisms of Atelectasis
Mechanical ventilation can lead to atelectasis through various mechanisms, including:
- Compression atelectasis: Positive pressure ventilation can push the diaphragm upward and compress the dependent lung regions, leading to atelectasis.
- Oxygen toxicity: High FiO2 settings can cause absorption atelectasis as oxygen replaces nitrogen in alveoli, leading to collapse when oxygen is absorbed into the bloodstream.
- Inadequate PEEP: Failing to keep alveoli open during exhalation can result in cyclic opening and closing of alveoli, promoting collapse.
- Ventilator-associated lung injury: Excessive tidal volumes can damage surfactant-producing cells, reducing surfactant production and increasing surface tension in alveoli, making them prone to collapse.
Prevention of Atelectasis
To minimize ventilator-induced atelectasis, the following strategies can be employed:
- Use of lung-protective ventilation with low tidal volumes (6-8 ml/kg) and appropriate PEEP levels (typically 5-10 cmH2O) 1.
- Minimization of FiO2 to the lowest level maintaining adequate oxygenation.
- Performance of regular recruitment maneuvers when indicated, as they can help reopen collapsed alveoli and improve lung mechanics 1.
- Encouragement of early mobilization when possible, as it can help prevent atelectasis by promoting normal sighing and deep breathing patterns.
Recent Recommendations
Recent studies and expert consensus-based recommendations suggest that lung-protective ventilation strategies, including the use of low tidal volumes and appropriate PEEP levels, can reduce postoperative pulmonary complications and improve outcomes 1. The use of PEEP levels between 5-10 cmH2O is recommended as a starting point, with adjustments made based on individual patient needs and response to therapy 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 2, 3, 4, 5
- Lack of recruitment maneuvers 3, 6, 4
- Use of high fractions of oxygen in inspired gas during induction and maintenance of anesthesia 6
- Low tidal volume ventilation strategy without proper PEEP and recruitment maneuver settings 3
Effects of PEEP and Recruitment Maneuvers
Studies have shown that:
- Individualized PEEP settings can optimize intraoperative mechanical ventilation and reduce postoperative atelectasis 4
- Recruitment maneuvers followed by titrated PEEP can improve lung volumes, respiratory system elastance, and oxygenation 2
- PEEP alone can minimize atelectasis formation in nonabdominal surgery 5
- Low PEEP without recruitment maneuvers is not suggested, as it can lead to decreased oxygenation and increased atelectasis 3
Prevention and Treatment of Atelectasis
To prevent or treat atelectasis, the following strategies can be used:
- Application of positive end-expiratory pressure (PEEP) 2, 3, 4, 5
- Recruitment maneuvers, such as inflation of the lungs to an airway pressure of 40 cm H2O, maintained for 7-8 seconds 6
- Use of a gas mixture with a poorly absorbed gas, such as nitrogen, during induction of anesthesia 6
- Ventilation with a moderate fraction of inspired oxygen (FIO2, e.g. 0.3-0.4) during maintenance of anesthesia 6