Comparing lung mechanics of patients with COVID related respiratory distress syndrome versus non-COVID acute respiratory distress syndrome: a retrospective observational study

Abstract

Background Most patients admitted to the intensive care unit with coronavirus disease (COVID-19) develop severe respiratory failure. Understanding lung mechanics helps to guide protective mechanical ventilation, improve oxygenation, and reduce the ventilator induce lung injury. This study aims to describe lung mechanics characteristics of patients with COVID -19 related acute respiratory distress syndrome (CARDS) and to compare them with non-COVID-19 associated ARDS. Methods We performed a retrospective observational study of lung mechanics: plateau pressure (Pplat), Driving pressure (DP), Mechanical power (MPw), Elastic (dynamic) power (EdPw), Total ventilatory power (TPw), and oxygenation parameters (ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2), the ratio of arterial oxygen partial pressure to fractional inspired oxygen multiplied by PEEP [PaO2/(FiO2 x PEEP)], arterial and venous carbon dioxide partial pressure (PaCO2, PvCO2), and Ventilation dead space (VD) were measured and compared between the two groups after initiation of mechanical ventilation. Results 30 CARDS and 10 ARDS patients fulfilled the study requirements. We observed a significant higher MPw in the CARDS group (29.17 ± 8.29 J/min vs 15.78 ± 4.45 J/min, P 0.007), similarly observed with EdPw (256.7 ± 84.06 mJ/min vs 138.1 ± 39.15 mJ/min, P 0.01) and TPw (289.1 ± 84.51 mJ/min vs 161.5 ± 45.51, P 0.007). Inside the CARDS group, we found 2 subgroups, a low shunt subgroup and a higher shunt (Qs/Qt (%): 6.61 ± 2.46 for vs 40.3 ± 20.6, P 0.0009), however, between these two subgroups we didn’t find statistical differences on lung mechanic parameters but only in oxygenation parameters (PaO2/FiO2 and PaO2/FiO2*PEEP). When comparing these two subgroups with ARDS patients, we found more similarity between the low shunt CARDS and the ARDS patients on MP (R2 0.99, P 0.001), EdPw (R2 0.89, P 0.05) and TPw (R2 0.99, P 0.0009). Conclusions: Our study suggests important differences between CARDS and ARDS regarding mechanical parameters that could lead to more complicated management of CARDS patients and a higher prevalence of VILI. However due to the study limitations, a bigger study is necessary to corroborate our findings. Keywords: COVID-19, CARDS, ARDS, lung mechanics, VILI.