Positive end-expiratory pressure (PEEP) has been interwoven with acute respiratory distress syndrome (ARDS) since its first description by Ashbaugh et al. [1]. Thereafter, the potentially competing effects of PEEP on lung volume, gas-exchange, and hemodynamics were quickly recognized, prompting the first proposals for methods to optimize PEEP in the clinical setting. Eight years after the term ARDS was minted, a seminal study by Suter et al. [2] defined “optimal PEEP” as the value associated with best respiratory compliance. That level was associated with the best oxygen delivery and dead space reduction, even though PaO2 continued to increase at PEEP levels higher than the compliance-defined optimum. This thoughtful approach was based not only on arterial “oxygenation”, but also on hemodynamics and respiratory mechanics. Subsequent research regarding “best PEEP” has resembled the search for the “Holy Grail”, and has developed sequentially along three main lines: oxygenation, lung mechanics, and clinical trials.
Key Points
- PEEP and Oxygenation: Early PEEP strategies focused on improving oxygenation by reducing venous admixture. However, targeting oxygenation alone can lead to excessive PEEP levels, causing hemodynamic compromise and overdistension.
- Lung Mechanics-Based PEEP Titration: The pressure-volume relationship has been used to define optimal PEEP, but misconceptions persist. Improved compliance does not always indicate lung recruitment, as it may result from the better aeration of pre-existing open units rather than true recruitment.
- Recruitment and Derecruitment: Recruitment is inconsistently defined, varying between imaging-based assessments and mechanical response evaluations. Some methods assume that increased compliance reflects recruitment, but this is not always the case.
- Esophageal Pressure-Guided PEEP: Using esophageal pressure as a surrogate for pleural pressure has been proposed to personalize PEEP settings. However, clinical trials have not demonstrated clear outcome benefits from this approach.
- PEEP and Hemodynamic Considerations: PEEP-induced reductions in cardiac output are often overlooked. High PEEP levels can impair venous return and right ventricular function, potentially worsening oxygen delivery despite improved oxygenation indices.
- PEEP in Clinical Trials: Multiple randomized trials have compared high vs. low PEEP strategies, with meta-analyses suggesting potential benefits in specific subgroups. However, excessive PEEP with recruitment maneuvers has been linked to increased mortality.
- Balancing Oxygenation, Lung Protection, and Hemodynamics: The ideal PEEP must maintain oxygenation while preventing atelectrauma and overdistension. A PEEP of 10–12 cm H₂O is often a reasonable starting point, with adjustments based on gas exchange, compliance, and hemodynamic stability.
- Limitations of Fixed PEEP Tables: While PEEP tables provide a structured approach, they fail to account for individual patient variability. Dynamic PEEP reassessment is essential as lung mechanics evolve during ARDS progression and resolution.
- The Individualized PEEP Approach: Rather than seeking a universal “best PEEP,” clinicians should aim for a pragmatic balance: maintaining SpO₂ > 90%, minimizing FiO₂, avoiding excessive driving pressures, and preventing hemodynamic instability.
- Future Directions in PEEP Research: Advanced imaging techniques, electrical impedance tomography (EIT), and machine learning models may improve personalized PEEP selection in the future, but no single method currently guarantees optimal outcomes.
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