Inter-lung asymmetrical airway closure cause insufflation delay between lungs in acute hypoxemic respiratory failure

Electrical Impedance Tomography (EIT) can quantify ventilation in the two lungs and be used to measure the airway opening pressure (AOP) of each lung. Asymmetrical AOPs can cause inter-lung insufflation delay.

To assess the relation between AOP asymmetry and inter-lung insufflation delay at different PEEP levels.

Patients with acute hypoxemic respiratory failure and airway closure were included. Low-flow pressure-volume curves and EIT signal were recorded during controlled ventilation and for some patients in pressure support ventilation.

23 patients were studied, 22 patients had ARDS, 9 patients had asymmetrical airway closure with an AOP of 10 [6-13] cmH₂0 in the sicker lung (AOP_sicker) vs. 5 [3-9, ] cmH₂0 in the healthier lung. During a low flow inflation, the inter-lung inflation delay was 0 [0-112]ms vs. 1450 [375-2400]ms in patients without or with asymmetrical AOPs, p < 0.0001. This delay was correlated to the difference of AOP between the 2 lungs, Spearman R² = 0.800, p < 0.0001. During tidal ventilation, median delay was 0 [0-62] ms vs. 150 [50-355] ms in patients without vs. with asymmetry, p = 0.019. Setting PEEP at the crossing point of a decremental EIT-based PEEP trial decreased the inter-lung insufflation delay. During pressure support insufflation delay could still be measured and was reduced by increasing PEEP from 5 to 10 cmH₂O in patient with asymmetrical lung injury.

In asymmetrical airway closure, titrating PEEP can minimize inter-lung insufflation delay and can be monitored by EIT. Reducing the delay and reducing ventilation asymmetry is also feasible during pressure support ventilation when low flow inflation curves cannot be performed.