In patients requiring mechanical ventilation for acute respiratory distress syndrome (ARDS) related to COVID-19, combining the lung ultrasound (LUS) aeration score and the recruitment-to-inflation ratio (R/I) can provide additional information on lung recruitment, according to the results from a prospective observational study published in the American Journal of Respiratory and Critical Care Medicine.

Applying optimal positive end-expiratory pressure (PEEP) to ensure lung recruitment while limiting lung hyperinflation remains a challenge for patients with COVID-19 admitted to intensive care units requiring mechanical ventilation for ARDS. The LUS aeration score and the R/I have the potential to identify patients who are more likely to benefit from PEEP and may provide information on lung recruitment.

Researchers in France studied 24 consecutive adult patients with COVID-19-related ARDS in whom PEEP-induced lung recruitment was assessed simultaneously with both the LUS and the R/I ratio within the first 48 hours after intubation. Most patients (n=22/24; 92%) presented with moderate to severe ARDS, and complete airway closure was present in one third of cases. The median R/I ratio was 0.7, thus defining 12 patients as high recruiters and 12 patients as low recruiters. LUS scores measured at low and high PEEP did not significantly differ between the 2 subgroups, whereas both ΔLUS and LUS reaeration scores were significantly higher in patients who were considered high recruiters.

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The difference in LUS reaeration scores was mainly driven by more reaeration in lateral and posterior lung regions in the recruiters. The researchers also found significant (P <.01) correlations between the R/I ratio and both ΔLUS and LUS reaeration scores, and these correlations were even stronger (P <.001) when considering only patients without complete airway closure.

The authors concluded, “The main and new finding of the present study is that the R/I ratio at a threshold of 0.7 correlated with the LUS reaeration score, in particular in patients without complete airway closure.”


Stevic N, Chatelain E, Dargent A, Argaud L, Cour M, Guérin C. Lung recruitability evaluated by recruitment-to-inflation ratio and lung ultrasound in COVID-19 acute respiratory distress syndrome. Am J Respir Crit Care Med. Published online February 8, 2021. doi:10.1164/rccm.202012-4447LE