Derecruitment of the lung induced by stepwise lowering of positive end-expiratory pressure in patients with adult respiratory distress syndrome.

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.