Lung response to a higher positive end-expiratory pressure in mechanically ventilated patients with COVID-19

Protti, Alessandro; Santini, Alessandro; Pennati, Francesca; Chiurazzi, Chiara; Cressoni, Massimo; Ferrari, Michele; Iapichino, Giacomo E.; Carenzo, Luca; Lanza, Ezio; Picardo, Giorgio; Caironi, Pietro; Aliverti, Andrea; Cecconi, Maurizio

Background International guidelines suggest using a higher (>10 cmH2O) positive end-expiratory pressure (PEEP) in patients with moderate-to-severe acute respiratory distress syndrome (ARDS) due to the novel coronavirus disease (COVID-19). However, even if oxygenation generally improves with a higher PEEP, compliance and arterial carbon dioxide tension (PaCO2) frequently do not, as if recruitment was small. Research question Is the potential for lung recruitment small in patients with early ARDS due to COVID-19? Study design and methods Forty patients with ARDS due to COVID-19 were studied in the supine position within three days of endotracheal intubation. They all underwent a PEEP trial, where oxygenation, compliance, and PaCO2 were measured with 5, 10, and 15 cmH2O of PEEP and all other ventilatory settings unchanged. Twenty underwent a whole-lung static computed tomography at 5 and 45 cmH2O, and the other twenty at 5 and 15 cmH2O of airway pressure. Recruitment and hyperinflation were defined as a decrease in the volume of the non-aerated (density above -100 HU) and an increase in the volume of the over-aerated (density below -900 HU) lung compartments, respectively. Results From 5 to 15 cmH2O, oxygenation improved in thirty-six (90%) patients but compliance only in eleven (28%) and PaCO2 only in fourteen (35%). From 5 to 45 cmH2O, recruitment was 351 (161-462) ml and hyperinflation 465 (220-681) ml. From 5 to 15 cmH2O, recruitment was 168 (110-202) ml and hyperinflation 121 (63-270) ml. Hyperinflation variably developed in all patients and exceeded recruitment in more than half of them. Interpretation Patients with early ARDS due to COVID-19, ventilated in the supine position, present with a large potential for lung recruitment. Even so, their compliance and PaCO2 do not generally improve with a higher PEEP, possibly due to hyperinflation.