Lu Chen1,2,3, Lorenzo Del Sorbo3,4, Domenico L Grieco5, Detajin Junhasavasdikul6, Nuttapol Rittayamai7, Ibrahim Soliman8, Michael C Sklar3, Michela Rauseo9, Niall D Ferguson3,4, Eddy Fan3,4, Jean-Christophe M Richard10, Laurent Brochard1,2,3. 1. Keenan Research Centre and Li Ka Shing Institute, Department of Critical Care, St. Michael's Hospital, Toronto, Ontario, Canada. 2. Interdepartmental Division of Critical Care Medicine, and. 3. Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada. 4. Division of Respirology and Critical Care Medicine, Toronto General Hospital, Toronto, Ontario, Canada. 5. Istituto di Anestesia e Rianimazione, Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy. 6. Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, and. 7. Division of Respiratory Diseases and Tuberculosis, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand. 8. Critical Care Department, King Saud Medical City, Riyadh, Saudi Arabia. 9. Anestesia e Rianimazione, Ospedali Riuniti di Foggia, Foggia, Italy; and. 10. Emergency Department, General Hospital of Annecy, Annecy, France.
Abstract
Rationale: Response to positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome depends on recruitability. We propose a bedside approach to estimate recruitability accounting for the presence of complete airway closure. Objectives: To validate a single-breath method for measuring recruited volume and test whether it differentiates patients with different responses to PEEP. Methods: Patients with acute respiratory distress syndrome were ventilated at 15 and 5 cm H2O of PEEP. Multiple pressure-volume curves were compared with a single-breath technique. Abruptly releasing PEEP (from 15 to 5 cm H2O) increases expired volume: the difference between this volume and the volume predicted by compliance at low PEEP (or above airway opening pressure) estimated the recruited volume by PEEP. This recruited volume divided by the effective pressure change gave the compliance of the recruited lung; the ratio of this compliance to the compliance at low PEEP gave the recruitment-to-inflation ratio. Response to PEEP was compared between high and low recruiters based on this ratio.Measurements and Main Results: Forty-five patients were enrolled. Four patients had airway closure higher than high PEEP, and thus recruitment could not be assessed. In others, recruited volume measured by the experimental and the reference methods were strongly correlated (R2 = 0.798; P < 0.0001) with small bias (-21 ml). The recruitment-to-inflation ratio (median, 0.5; range, 0-2.0) correlated with both oxygenation at low PEEP and the oxygenation response; at PEEP 15, high recruiters had better oxygenation (P = 0.004), whereas low recruiters experienced lower systolic arterial pressure (P = 0.008).Conclusions: A single-breath method quantifies recruited volume. The recruitment-to-inflation ratio might help to characterize lung recruitability at the bedside.Clinical trial registered with www.clinicaltrials.gov (NCT02457741).
Rationale: Response to positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome depends on recruitability. We propose a bedside approach to estimate recruitability accounting for the presence of complete airway closure. Objectives: To validate a single-breath method for measuring recruited volume and test whether it differentiates patients with different responses to PEEP. Methods: Patients with acute respiratory distress syndrome were ventilated at 15 and 5 cm H2O of PEEP. Multiple pressure-volume curves were compared with a single-breath technique. Abruptly releasing PEEP (from 15 to 5 cm H2O) increases expired volume: the difference between this volume and the volume predicted by compliance at low PEEP (or above airway opening pressure) estimated the recruited volume by PEEP. This recruited volume divided by the effective pressure change gave the compliance of the recruited lung; the ratio of this compliance to the compliance at low PEEP gave the recruitment-to-inflation ratio. Response to PEEP was compared between high and low recruiters based on this ratio.Measurements and Main Results: Forty-five patients were enrolled. Four patients had airway closure higher than high PEEP, and thus recruitment could not be assessed. In others, recruited volume measured by the experimental and the reference methods were strongly correlated (R2 = 0.798; P < 0.0001) with small bias (-21 ml). The recruitment-to-inflation ratio (median, 0.5; range, 0-2.0) correlated with both oxygenation at low PEEP and the oxygenation response; at PEEP 15, high recruiters had better oxygenation (P = 0.004), whereas low recruiters experienced lower systolic arterial pressure (P = 0.008).Conclusions: A single-breath method quantifies recruited volume. The recruitment-to-inflation ratio might help to characterize lung recruitability at the bedside.Clinical trial registered with www.clinicaltrials.gov (NCT02457741).
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