Recruitment manoeuvres: more studies or just more PEEP?

Introduction. Mechanical ventilation may induce lung injury when leading to unphysiological stress and strain, inflammatory response and mechanical lesions. The widely accepted “lung protective strategy” includes low tidal volume ventilation, airway plateau pressures limited to 30 cmH2O and a PEEP value sufficient to prevent the intra-tidal collapse of pulmonary units. Description of review. The adequate individual PEEP selection and its efficacy in lung injury prevention has not been proved and is still subject of debate and the most recent and largest clinical studies on PEEP application were not able to find any difference in outcome between patients ventilated with high vs. low PEEP values. However, two meta-analyses suggested outcome benefit of higher PEEP in more severe ARDS and possible harm in patients with mild ARDS It is conceivable, that the best way for setting PEEP is the severity of the pathology and the potential for lung recruitment, which may be quantified, by CT scan, as a gain of aeration of previously non aerated lung tissue. Several methods for selecting PEEP at bedside have been proposed in clinical trials: lung mechanics (ExPress, Stress Index studies), esophageal pressure and oxygenation (higher PEEP table of LOV study). The LOV method appears the only one which selects a PEEP somehow related to lung recruitability while the other are unrelated. Conclusion. A randomized study testing the application of higher and lower PEEP levels in higher and lower recruiter patients will be necessary, however it will imply ethical problems and several years to recruit the necessary population. In the meantine the suggestion is that if recruitability cannot be measured by CT scan, systemic arterial oxygenation seems the most clinically sound method to evaluate it at bedside in order to avoid lower recruiters patients the risk of higher PEEP to keep open few grams of lung.