Respiratory effects of lung recruitment maneuvers depend on the recruitment-to-inflation ratio in patients with COVID-19-related acute respiratory distress syndrome.

BACKGROUND

In the context of acute respiratory distress syndrome (ARDS), the response to lung recruitment maneuvers (LRMs) varies considerably from one patient to another and so is difficult to predict. The aim of the study was to determine whether or not the recruitment-to-inflation (R/I) ratio could differentiate between patients according to the change in lung mechanics during the LRM.

METHODS

We evaluated the changes in gas exchange and respiratory mechanics induced by a stepwise LRM at a constant driving pressure of 15 cmHO during pressure-controlled ventilation. We assessed lung recruitability by measuring the R/I ratio. Patients were dichotomized with regard to the median R/I ratio.

RESULTS

We included 30 patients with moderate-to-severe ARDS and a median [interquartile range] R/I ratio of 0.62 [0.42-0.83]. After the LRM, patients with high recruitability (R/I ratio ≥ 0.62) presented an improvement in the PO/FO ratio, due to significant increase in respiratory system compliance (33 [27-42] vs. 42 [35-60] mL/cmHO; p < 0.001). In low recruitability patients (R/I < 0.62), the increase in PO/FO ratio was associated with a significant decrease in pulse pressure as a surrogate of cardiac output (70 [55-85] vs. 50 [51-67] mmHg; p = 0.01) but not with a significant change in respiratory system compliance (33 [24-47] vs. 35 [25-47] mL/cmHO; p = 0.74).

CONCLUSION

After the LRM, patients with high recruitability presented a significant increase in respiratory system compliance (indicating a gain in ventilated area), while those with low recruitability presented a decrease in pulse pressure suggesting a drop in cardiac output and therefore in intrapulmonary shunt.