Extravascular lung water (EVLW) does not change during alveolar recruitment in acute respiratory distress syndrome (ARDS)

Objectives

To evaluate the relationship between the PaO₂/FiO₂ ratio and EVLW during alveolar recruitment at different positive end expiratory pressure (PEEP) levels in ARDS in a prospective clinical trial.

Materials and methods

Ten patients suffering from ARDS were recruited. All patients were ventilated in pressure control mode (FiO₂ = 1.0, respiratory rate = 20, I:E = 1:1). Following basic haemodynamic measurements and blood gas analysis, alveolar recruitment was done: PEEP was set at 26 cmH₂O then 40 cmH₂O pressure amplitude was applied for 40 s. Optimal PEEP was determined as follows: tidal volume was reduced to 4 ml/kg, then the PEEP was reduced from 26 cmH₂O by 2 cmH₂O in every 4 min and the optimal PEEP was defined as 2 cmH₂O above the level of PEEP, where the PaO₂ suddenly dropped by > 10%. After setting the PEEP at the optimal level, the 40/40 manoeuvre was applied again and the tidal volume was set as 6 ml/kg. The FiO₂ was left at 100% until the end of the trial period of 1 hour. Haemodynamic parameters were determined by arterial thermodilution (PiCCO) on entering the study, then during the optimal PEEP defining process every 8 min, and 30 and 60 min after. Data are presented as mean ± SD. For statistical analysis multiple regression analysis, and analysis of variance (ANOVA) was used, respectively.

Results

The initially applied PEEP and the determined optimal PEEP did not differ significantly. Compared with baseline (T0) the PaO₂ was significantly higher following alveolar recruitment (T_ep) and also after 60 min. The EVLW did not change significantly during the study period (Table 1). Regression analysis could not reveal any significant relationship between PaO₂ and EVLW at different PEEP.

Table 1

Discussion

Recently we found significant correlation between EVLW and PaO₂/FiO₂ and PEEP levels. To date no clinical trials reported the relationship between oxygenation and EVLW during alveolar recruitment and PEEP optimisation. Based on the current results of this pilot study it seems that the EVLW does not directly affect oxygenation during recruitment. Completion of the study is required to evaluate the effect of EVLW on the optimal PEEP in ARDS.