Effect of pleural effusion on gas exchange and response to positive end-expiratory pressure in acute lung injury/acute respiratory distress syndrome patients

Introduction

Pleural effusion is a common finding in acute lung injury/acute respiratory distress syndrome (ALI/ARDS) patients. However, the effect of pleural effusion on gas exchange, respiratory mechanics and response to positive end-expiratory pressure (PEEP) in ALI/ARDS patients, during mechanical ventilation, has never been prospectively studied.

Methods

Patients with a diagnosis of ALI/ARDS, who underwent a CT scan at 5 cmH₂O PEEP for clinical reasons, were included in the study. Lung and pleural effusion were outlined separately; lung total weight and pleural effusion volume were computed with dedicated software. A PEEP test at 5 and 15 cmH₂O with constant minute ventilation was performed. Exclusion criteria were: age <18 years, hemodynamic instability, chronic obstructive pulmonary disease and evidence of barotrauma.

Results

We enrolled 11 ALI/ARDS patients (10 male). The mean clinical characteristics on admission to the ICU were: age 67.5 ± 9.9 years, BMI 24.4 ± 2.1 kg/m², PaO₂/FiO₂ 203.1 ± 56.1 mmHg, PEEP 9.1 ± 2.8 cmH₂O and pH 7.394 ± 0.048. The volume of pleural effusion was not significantly related with the change in PaCO₂ (r² = 0.068; P = 0.437), PaO₂ (r²= 0.015; P = 0.722) and dead space (VD/VT) (r² = 0.019; P = 0.682) going from PEEP 15 to PEEP 5 cmH₂O.

Conclusion

Pleural effusion does not seem to influence the gas-exchange response to PEEP.