Functional respiratory imaging to evaluate PEEP induced bronchial and Alveolar recruitment in ARDS patients

Rationale Insights in the pathophysiology of ARDS, the most severe form of acute lung injury, mainly point towards alveoli. Recently, airway morphological changes and dysfunction have been demonstrated too. Although it is established that increasing PEEP levels assist in the recruitment of alveoli in ARDS patients to decrease hypoxemia, today no imaging technique was able to easily quantify the diameter of airways or to demonstrate if airways can also be recruited in ventilated ARDS patients. For this purpose, we aimed to use functional respiratory imaging (FRI) as an innovative imaging technique to evaluate whether incremental PEEP levels induced not only alveolar but also bronchial recruitment in ARDS. Methods Static lung compliance values are measured using a low flow inflation generated pressure-volume curve. The lower infliction point is considered as the clinically acceptable minimal PEEP value. Subsequently, 4 distinct PEEP levels are chosen to perform end-expiratory breath hold CT scans: 1) 20 cmH2O; 2) median value between 1 and 3; 3) clinically acceptable minimal; 4) 0 cmH2O. The 4 sequential CT scans are executed from high to low PEEP levels with a 2-minute stabilization period in between the scans, using volume-controlled ventilation. FRI methods as described by De Backer et al. (Radiology:257(3), 2010) were used to evaluate airway morphology. Results Results from 2 patients (male; 78 and 40 year old, at [0-8-14-20] and [0-6-13-20] cmH2O PEEP) show that not only alveolar but also bronchial recruitment occurred and were most pronounced in the lower lobes. Bronchial recruitment occurs even more rapidly than alveolar recruitment (Figure 1). Conclusions Using FRI it was possible to evaluate and differentiate between PEEP induced bronchial and alveolar recruitment in ARDS patients. Additional ARDS patients, who are mechanically ventilated, are currently included in this trial after signing informed consent by their closest relative. Remaining patients are / will be included in Q4 of 2013. Full results will be available in Q1 of 2014