Inspiratory and end-expiratory effects of lung recruitment in the prone position on dorsal lung aeration – new physiological insights in a secondary analysis of a randomised controlled study in post-cardiac surgery patients

BACKGROUND: Cardiac surgery produces dorso-basal atelectasis and ventilation/perfusion mismatch, associated with infection and prolonged intensive care. A postoperative lung volume recruitment manoeuvre to decrease the degree of atelectasis is routine. In patients with severe respiratory failure, prone positioning and recruitment manoeuvres may increase survival, oxygenation, or both. We compared the effects of lung recruitment in prone vs supine positions on dorsal inspiratory and end-expiratory lung aeration. METHODS: In a prospective RCT, 30 post-cardiac surgery patients were randomly allocated to recruitment manoeuvres in the prone (n=15) or supine position (n=15). The primary endpoints were late dorsal inspiratory volume (arbitrary units [a.u.]) and left/right dorsal end-expiratory lung volume change (a.u.), prone vs supine after extubation, measured using electrical impedance tomography. Secondary outcomes included left/right dorsal inspiratory volumes (a.u.) and left/right dorsal end-expiratory lung volume change (a.u.) after prone recruitment and extubation. RESULTS: The last part of dorsal end-inspiratory volume after extubation was higher after prone (49.1 a.u.; 95% confidence interval [CI], 37.4–60.6) vs supine recruitment (24.2 a.u.; 95% CI, 18.4–29.6; P=0.024). Improvement in left dorsal end-expiratory lung volume after extubation was higher after prone (382 a.u.; 95% CI, 261–502) vs supine recruitment (–71 a.u., 95% CI, –140 to –2; n=15; P<0.001). After prone recruitment, left vs right predominant end-expiratory dorsal lung volume change disappeared after extubation. However, both left and right end-expiratory volumes were higher in the prone group, after extubation. CONCLUSIONS: Recruitment in the prone position improves dorsal inspiratory and end-expiratory lung volumes after cardiac surgery. CLINICAL TRIAL REGISTRATION: NCT03009331.