Lung recruitment and hyperinflation with higher positive end-expiratory pressure in COVID-19: a computed tomography study (preprint)

Background A higher (> 10 cmH2O) positive end-expiratory pressure (PEEP) is commonly used in patients with moderate to severe hypoxemia due to the novel coronavirus disease (COVID-19). However, compliance more commonly decreases when PEEP is increased from 10 to 15 cmH2O, as for lung hyperinflation. In this study, we directly measured lung recruitment and hyperinflation induced by increasing PEEP from 10 to 15 cmH2O in mechanically ventilated patients with COVID-19.Methods Twenty mechanically ventilated patients with COVID-19 underwent a lung computed tomography (CT) at 10 and 15 cmH2O of airway pressure. Gas exchange and compliance were then measured with 10 and 15 cmH2O of PEEP. Recruitment was computed as the decrease of the non-aerated lung volume (density above − 100 HU) and hyperinflation as the increase of the over-aerated lung volume (density below − 900 HU). If recruitment was larger than hyperinflation, the net morphological response was “recruitment”; otherwise, it was “hyperinflation”.Results With 10 cmH2O of PEEP, the median (Q1-Q3) arterial tension to the inspiratory fraction of oxygen (PaO2:FiO2) was 146 (107–197) mmHg. The net morphological response to increasing PEEP was recruitment in nine (45%) patients and hyperinflation in eleven (55%). Oxygenation improved in twelve (60%) patients, but compliance in only three (15%). Compliance with 10 cmH2O of PEEP ≤ 45 cmH2O/ml predicted net recruitment in response to increasing PEEP with a positive predictive value of 0.89 (95%-confidence intervals: 0.49-1.00) and a negative predictive value of 0.91 (0.59-1.00).Conclusions The morphological response to a higher PEEP is largely variable in patients with COVID-19, ranging from net recruitment (in half of the patients) to net hyperinflation (in the other half). Baseline compliance may help to predict the individual response to increasing PEEP.

Lung Response to Prone Positioning in Mechanically-ventilated Patients With COVID-19 (preprint)

Background: Prone positioning improves survival in moderate-to-severe acute respiratory distress syndrome (ARDS) unrelated to the novel coronavirus disease (COVID-2019). This benefit is probably mediated by a decrease in alveolar collapse and hyperinflation and a more homogeneous distribution of lung aeration, with fewer harms of mechanical ventilation. Herein we aimed to verify whether prone positioning causes analogue changes in lung aeration in COVID-2019. A positive result would support prone positioning even in this other population. MethodsFifteen mechanically-ventilated patients with COVID-19 underwent a lung computed tomography in the supine and prone position within three days of endotracheal intubation and with a constant positive end-expiratory pressure (PEEP). Using quantitative analysis, we measured the volume of the non-aerated, poorly-aerated, well-aerated, and over-aerated compartments and the gas-to-tissue ratio of the ten vertical levels of the lung. In addition, we expressed the heterogeneity of lung aeration with the standardized median absolute deviation of the ten vertical gas-to-tissue ratios, with lower values indicating less heterogeneity. ResultsBy the time of the study, PEEP was 12 (10-14) cmH 2 O and the PaO 2 FiO 2 107 (84-173) mmHg in the supine position. With prone positioning, the volume of the non-aerated compartment decreased by 82 (26-147) ml, of the poorly-aerated compartment increased by 82 (53-174) ml, of the normally-aerated compartment did not significantly change, and of the over-aerated compartment decreased by 28 (11-186) ml. In eight (53%) patients, the volume of the over-aerated compartment decreased more than the volume of the non-aerated compartment. The gas-to-tissue ratio of the ten vertical levels of the lung decreased by 0.34 (0.25-0.49) ml/g per level in the supine position and by 0.03 (-0.11-0.14) ml/g in the prone position (p<0.001). The standardized median absolute deviation of the gas-to-tissue ratios of those ten levels decreased in all patients, from 0.55 (0.50-0.71) to 0.20 (0.14-0.27) (p<0.001).ConclusionsIn fifteen patients with COVID-19, prone positioning decreased alveolar collapse and hyperinflation, and homogenized lung aeration. A similar response has been observed in other ARDS, where prone positioning improves outcome. Therefore, our data provide a pathophysiological rationale to support prone positioning even in COVID-19.