Assessment of static compliance and estimated lung recruitment as a tool for PEEP setting in ARDS patients

Introduction

Different techniques to determine optimal PEEP setting in patients with ARDS have been suggested. The aim of our study was to evaluate assessment of static compliance of respiratory system in combination with estimated lung recruitment [1] for selection of PEEP setting with minimal Qs/Qt.

Methods

Seven patients with early ARDS (intubation time < 7 days) with pulmonary artery catheter in place were studied. During the study all patients were ventilated at different PEEP levels using CMV with constant inspiratory flow, tidal volume was 5-7 ml/kg IBW, inspiratory/exspiratory time and respiratory rate was adjusted to avoid presence of intrinsic PEEP. On each level of PEEP arterial and mixed venous blood gases, hemodynamic parameters, static compliance of respiratory system Crs and difference in endexpiratory lung volumes ?EELV_PEEPtest between tested and baseline level of PEEP (minimal level of PEEP used during the study, usually 8 cmH₂O) were recorded. Volumes and pressures were measured using CP-100 pulmonary monitor (BICORE monitoring systems, USA) at the end of airway. Estimated lung recruitment ELR (ELR_PEEPtest = ?EELV_PEEPtest - Crs_PEEPtest × [PEEP_test -PEEP_baseline]) was calculated for each tested level of PEEP. Ability to predict the PEEP level with minimal shunt was tested for minimal PEEP with maximal Crs, for maximal PEEP with maximal Crs and for algorithm based on static compliance and the amount of estimated lung recruitment. Sensitivity, specificity and likelihood ratio (LR) for prediction of PEEP level with minimal shunt were calculated, Fisher exact test was used for statistical analysis, P < 0.05^* was considered statistically significant.

Results

Table 1

Conclusion

Despite limited number of patients and possible influence of used equipment on critical value of ELR we found that combined assessment of compliance and recruited lung volume enables better prediction of PEEP setting with minimal Qs/Qt.