Distribution of airway pressure opening in the lungs measured with electrical impedance tomography (POET): a prospective physiological study

Background: In patients with acute hypoxemic respiratory failure (AHRF) under mechanical ventilation, the change in pressure slope during a low-flow insufflation indicates a global airway opening pressure (AOP) needed to reopen closed airways and may be used for titration of positive end-expiratory pressure.

Objectives: To understand 1) if airways open homogeneously inside the lungs or significant regional AOP variations exist; 2) whether the pattern of the pressure slope change during low-flow insufflation can indicate the presence of regional AOP variations.

Methods: Using electrical impedance tomography, we recorded low-flow insufflation maneuvers (< 10 L/min) starting from end-expiratory positive pressure 0-5 cmH₂O. We measured global (AOP_global) and regional AOPs from pressure-impedance curves in the four different lung quadrants, and compared AOP_global with the highest quadrantal AOP (AOP_highest). We categorized the slope change of the low-flow inflation pressure-time curve into three patterns: no change, progressive change, abrupt change.

Results: Among the 36 patients analyzed, 9 (25%) had AOP_global ≥ 5 cmH₂O whereas 19 (53%) exhibited regional AOP_highest ≥ 5 cmH₂O. AOP_global was on average similar to AOP of the upper right quadrant (P = 0.182) but was lower than AOPs of the other three quadrants (P < 0.01 of each). AOP_global was significantly lower than AOP_highest: 3.0 [2.0-4.3] vs. 5.0 [2.8-8.3] cmH₂O, P < 0.001. AOP was higher in the dependent than the non-dependent ventilated lung (4.0 [2.0-6.3] vs. 3.0 [2.0-5.0] cmH₂O, P < 0.001). Seventeen (47%) patients exhibited a 'progressive change' pattern in the pressure-time curve. These patients had a larger difference between AOP_highest and AOP_global (3.0 [2.0-4.0] cmH₂O with a maximum of 8 cmH₂O) compared to the other two patterns: 1.0 [0-1.0] cmH₂O in 'no change' , P < 0.001 and 1.0 [0-2.0] cmH₂O in 'abrupt change' , P = 0.003.

Conclusion: AOP_global mostly reflects the lowest opening pressure in the lung and frequently underestimates the highest regional AOP in mechanically ventilated patients with AHRF. A progressive slope change during the low-flow pressure-time curve indicates the presence of several and higher regional AOPs.

Trial registration: Clinicaltrials.gov, NCT05825534 (registered, April 24th, 2023), retrospectively registered.