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 cmH 2 O. 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 cmH 2 O whereas 19 (53%) exhibited regional AOP highest ≥ 5 cmH 2 O. 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] cmH 2 O, 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] cmH 2 O, 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] cmH 2 O with a maximum of 8 cmH 2 O) compared to the other two patterns: 1.0 [0–1.0] cmH 2 O in ‘no change’ , P < 0.001 and 1.0 [0–2.0] cmH 2 O 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, NCT 05825534 (registered, April 24th, 2023), retrospectively registered.