However, we have previously reported that PP allows recruitment of a slow compartment previously excluded from ventilation. suggested, on the basis of pooled data from randomized, controlled trials, that PP may improve survival in the subgroup of patients with the most severe ARDS, that is, those with a ratio of partial pressure of arterial O 2 to fraction of inspired O 2 (PaO 2/FiO 2) 20 mmHg after one to six hours in the PP. This method was proposed more than 30 years ago, initially in pathophysiological studies.

The prone position (PP) may also be part of the ventilatory strategy.

The application of positive end-expiratory pressure (PEEP) is recognized to recruit the lung and to restore functional residual capacity, but its optimum level is still widely debated. In particular, a strict limitation of tidal volume (V T) and plateau pressure (Pplat) below 30 cmH 2O reduces mortality. Considerable progress has been made over the past decade in the ventilatory management of patients with ARDS.

Since its first description in 1967, it has been accepted that acute respiratory distress syndrome (ARDS) includes a number of lung injuries of various origins whose consequences are decreased lung capacity available for ventilation, leading to the concept of 'baby lung'. Estimated VD physiol/V T ratios significantly underestimated measured VD physiol/V T ratios (concordance correlation coefficient 0.19 (interquartile ranges 0.091 to 0.28)), whereas changes during PP were more reliable (concordance correlation coefficient 0.51 (0.32 to 0.66)). When the response was defined by PaCO 2, four patients were differently classified, and responders ( n = 7) had a greater decrease in VD alv/V T ratio and in Pplat and a greater increase in PaO 2/FiO 2 ratio and in Crs than nonresponders ( n = 6). When the response was defined by PaO 2/FiO 2 ratio, no significant differences in Pplat, PaCO 2 or VD alv/V T alterations between responders ( n = 7) and nonresponders ( n = 6) were observed. Changes in VD alv/V T were correlated with changes in Crs, but not with changes in PaO 2/FiO 2 ratios. Maximal changes were observed after six to nine hours. PP induced a decrease in Pplat, PaCO 2 and VD alv/V T ratio and increases in PaO 2/FiO 2 ratios and compliance of the respiratory system (Crs).

Alveolar dead space paco2