Is there a role of extravascular lung water (EVLW) in the development of atelectasis in ARDS?

Objectives

To evaluate the relationship between PaO₂/FiO₂ ratio and EVLW in septic shock induced ARDS in a prospective observational clinical trial.

Materials and methods

Twenty-three patients suffering from sepsis-induced ARDS were recruited. All patients were ventilated in pressure control/support mode. Haemodynamic parameters were determined by arterial thermodilution (PiCCO) 8 hourly for 72 hours. At the same time blood gas analyses were done and respiratory parameters were also recorded. Data are presented as mean ± SD. For statistical analysis, Pearson's correlation test, and analysis of variance (ANOVA) was used, respectively.

Results

Significant negative correlation was found between EVLW and PaO₂/FiO₂ (r = -0.355, P < 0.001), and significant positive correlation was shown between EVLW and PEEP (r = 0.557, P < 0.001). A post-hoc analysis was also performed when 'low' PEEP (< 10 cmH₂O) and 'high' PEEP (≥ 10 cmH₂O) were applied (Table 1).

Table 1

Discussion

Several animal trials reported contradicting results on the effect of PEEP on EVLW [1]. We found significant correlation between EVLW and PaO₂/FiO₂ and PEEP. Furthermore, patients with increase EVLW required higher PEEP, while none of the other parameters differed significantly when 'high' or 'low' PEEP were applied. Based on the current results we assume that it is the EVLW that indirectly determines the required PEEP by playing a part in the development of alveolar atelectasis. Further studies are required to evaluate the clinical significance of this finding, for example in the fine-tuning of PEEP in ARDS.