Computed tomography assessment of PEEP-induced alveolar recruitment in patients with severe COVID-19 pneumonia

Abstract

Background There is a paucity of data concerning the optimal ventilator management in patients with COVID-19 pneumonia; particularly, the optimal levels of positive-end expiratory pressure (PEEP) are unknown. We aimed to investigate the effects of two levels of PEEP on alveolar recruitment in critically ill patients with severe COVID-19 pneumonia. Methods A single-center cohort study was conducted in a 39-bed intensive care unit at a university-affiliated hospital in Genoa, Italy. Chest computed tomography (CT) was performed to quantify aeration at 8 and 16 cmH 2 O PEEP. The primary endpoint was the amount of alveolar recruitment, defined as the change in the non-aerated compartment at the two PEEP levels on CT scan. Results Forty-two patients were included in this analysis. Alveolar recruitment was median [interquartile range] 2.7 [0.7–4.5] % of lung weight and was not associated with excess lung weight, PaO 2 /FiO 2 ratio, respiratory system compliance, inflammatory and thrombophilia markers. Patients in the upper quartile of recruitment (recruiters), compared to non-recruiters, had comparable clinical characteristics, lung weight and gas volume. Alveolar recruitment was not different in patients with lower versus higher respiratory system compliance. In a subgroup of 20 patients with available gas exchange data, increasing PEEP decreased respiratory system compliance (median difference, MD − 9\xa0ml/cmH 2 O, 95% CI from − 12 to − 6\xa0ml/cmH 2 O, p \u2009<\u20090.001) and the ventilatory ratio (MD − 0.1, 95% CI from − 0.3 to − 0.1, p \u2009=\u20090.003), increased PaO 2 with FiO 2 \u2009=\u20090.5 (MD 24\xa0mmHg, 95% CI from 12 to 51\xa0mmHg, p \u2009<\u20090.001), but did not change PaO 2 with FiO 2 \u2009=\u20091.0 (MD 7\xa0mmHg, 95% CI from − 12 to 49\xa0mmHg, p \u2009=\u20090.313). Moreover, alveolar recruitment was not correlated with improvement of oxygenation or venous admixture. Conclusions In patients with severe COVID-19 pneumonia, higher PEEP resulted in limited alveolar recruitment. These findings suggest limiting PEEP strictly to the values necessary to maintain oxygenation, thus avoiding the use of higher PEEP levels.