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 (AOPglobal) and regional AOPs from pressure-impedance curves in the four different lung quadrants, and compared AOPglobal with the highest quadrantal AOP (AOPhighest). 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 AOPglobal ≥ 5 cmH2O whereas 19 (53%) exhibited regional AOPhighest ≥ 5 cmH2O. AOPglobal 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). AOPglobal was significantly lower than AOPhighest: 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 AOPhighest and AOPglobal (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 AOPglobal 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. Graphical abstract

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

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2025年1月16日

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Nannan Sun,
Clement Brault,
Antenor Rodrigues,
Matthew Ko,
Fernando Vieira,
Vorakamol Phoophiboon,
Michel Slama,
Lu Chen,
Laurent Brochard

摘要

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, NCT 05825534 (registered, April 24th, 2023), retrospectively registered.

Graphical abstract