Role of Alveolar-Arterial Difference in Estimation of Extravascular Lung Water in COVID-19-Related ARDS

Abstract

BACKGROUND:

The dominant feature of COVID-19-associated ARDS is gas exchange impairment. Extravascular lung water index is a surrogate for lung edema and reflects the level of alveolocapillary disruption. The primary aim was the prediction of extravascular lung water index by the alveolar-arterial oxygen difference. The secondary aims were in determining the relationship between the extravascular lung water index and other oxygenation parameters, the ${\mathbf{\text{F}}}_{{\mathbf{\text{IO}}}_{\mathbf{2}}}$ , end-tidal oxygen concentration, pulmonary oxygen gradient ( ${\mathbf{\text{F}}}_{{\mathbf{\text{IO}}}_{\mathbf{2}}}$ minus end-tidal oxygen concentration), and ${\mathbf{\text{P}}}_{{\mathbf{\text{aO}}}_{\mathbf{\text{2}}}}$ .

METHODS:

This observational prospective single-center study was performed at the Department of Anaesthesiology and Intensive Care, The University Hospital in Ostrava, The Czech Republic, during the COVID-19 pandemic, from March 20, 2020, until May 24, 2021.

RESULTS:

The relationship between the extravascular lung water index and alveolar-arterial oxygen difference showed only a mild-to-moderate correlation (r = 0.33, P < .001). Other extravascular lung water index correlations were as follows: ${\mathbf{\text{F}}}_{{\mathbf{\text{IO}}}_{\mathbf{2}}}$ (r = 0.33, P < .001), end-tidal oxygen concentration (r = 0.26, P = .0032), ${\mathbf{\text{F}}}_{{\mathbf{\text{IO}}}_{\mathbf{2}}}$ minus end-tidal oxygen concentration (r = 0.15, P = .0624), and ${\mathbf{\text{P}}}_{{\mathbf{\text{aO}}}_{\mathbf{\text{2}}}}$ (r = –0.15, P = .01).

CONCLUSIONS:

The alveolar-arterial oxygen difference does not reliably correlate with the extravascular lung water index and the degree of lung edema in COVID-19–associated ARDS.