Summary

Background and objective: It has recently been suggested that recruitment proceeds far above the lower inflection point of the elastic pressure–volume (Pel/V) curve of the respiratory system. Accordingly, the value of the lower inflection point as a guide to set the positive end-expiratory pressure (PEEP) has been challenged. Our aim was to evaluate the derecruitment induced by stepwise decreasing PEEP levels.

Methods: Seven consecutive sedated and paralysed patients with acute respiratory distress syndrome were studied. Multiple Pel/V curves of the respiratory system were recorded at PEEP levels progressively decreasing in steps of 3.75 cmH2O from +15 to zero according to the principles of the low flow inflation method.

Results: Multiple Pel/V curves shifted towards lower volumes at decreasing PEEP. Dynamic compliance was higher for Pel/V curves recorded from lower PEEP levels. A high correlation (r = 0.99) was found between dynamic compliance and PEEP. The lower inflection point was on average 9.2 cmH2O. However, the transition between the lower segment and the linear part of the Pel/V curve was in general smooth to the eye. The upper inflection point was on average 23.8 cmH2O. A high correlation (r = 0.98) between the upper inflection point and PEEP was found.

Conclusions: The lower inflection point is a poor indicator of alveolar closure. The evaluation of derecruitment induced by a stepwise reduction in PEEP seems to be more useful than individual titration of PEEP and tidal volume in patients with adult respiratory distress syndrome.