Functional respiratory imaging of the airways in the acute respiratory distress syndrome

Abstract

Background: Alveolar flooding and airway obstruction are present in the acute respiratory distress syndrome. The impact of positive end-expiratory pressure on regional airway aeration has not been described.

Aim: To assess bronchial and lung recruitment and distension during an incremental positive end-expiratory pressure trial in patients with acute respiratory distress syndrome.

Methods: Six patients underwent lung and airway imaging at four positive end-expiratory pressure levels in a cohort trial. Images were post-processed by means of Functional Respiratory Imaging. This technique offers 3-dimensional visualisation and quantification of patients' airway and lung geometry on a regional level.

Results: With increasing positive end-expiratory pressure from 0 to 20 cmH₂O, the median bronchial recruitment was 151% and the median bronchial distension 43%. Non-aerated lower lobes bronchi had more bronchial volume increase at high positive end-expiratory pressure than partially aerated upper lobes bronchi. Lung recruitment tended to be higher in patients with non-focal acute respiratory distress syndrome. In two patients, bronchial volume increase at high positive end-expiratory pressure largely exceeded bronchial volume increase observed in matched healthy control subjects at total lung capacity, suggesting severe bronchial over-distension.

Conclusions: In early acute respiratory distress syndrome, Functional Respiratory Imaging gives an innovative insight into the relationship between positive end-expiratory pressure-induced bronchial distension and recruitment, positive end-expiratory pressure-induced lung recruitment and hyperinflation and lung morphology.

Keywords: ARDS; Bronchial distension; Bronchial recruitment; Lung hyperinflation; Lung recruitment.