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Impact of PEEP on V/Q mismatch according to patient position and recruitability: a clinical prospective study
Zhiqian Zha1, Zhichang Wang1, Qiyu Cheng1
1Jiangsu Provincial Key Laboratory of Critical Care Medicine, Department of Critical Care Medicine, Zhongda Hospital, School of Medicine, Southeast University, Nanjing, 210009, China.
Background:
High positive end-expiratory pressure (PEEP) may improve ventilation-perfusion (V/Q) mismatch in acute respiratory distress syndrome (ARDS) patients with high recruitability in supine position. However, impacts of PEEP on V/Q mismatch in prone position relative to supine position remain poorly understood. We aimed to compare PEEP effects between positions, and evaluate its relationship with lung recruitability.
Methods:
A total of 50 patients with moderate-to-severe ARDS were consecutively enrolled. Recruitment-to-inflation (R/I) ratio was used to measure baseline lung recruitability. V/Q mismatch, gas exchange, and respiratory mechanics were evaluated at PEEP 5 cm H2O and PEEP 15 cm H2O in supine position, followed by PEEP 5 cm H2O and PEEP 15 cm H2O in prone position.
Results:
Median R/I ratio was 0.60 [0.38, 0.72], separating patients with higher and lower R/I ratio. In patients with higher R/I ratio, PEEP 15 cm H2O (compared to PEEP 5 cm H2O) reduced shunt without significantly increasing dead space in both supine and prone positions, thereby improving V/Q mismatch (supine: 30.7 [28.6, 36.8]% at PEEP 15 cm H2O vs.38.0 [34.9, 45.4]% at PEEP 5 cm H2O, P < 0.001; prone: 25.7 [21.4, 30.4]% at PEEP 15 cm H2O vs. 32.8 [27.5, 36.7]% at PEEP 5 cm H2O, P < 0.001). However, in patients with lower R/I ratio, PEEP 15 cm H2O (compared to PEEP 5 cm H2O) in supine position did not improve V/Q mismatch (37.8 [34.7, 42.1]% at PEEP 15 cm H2O vs. 41.3 [34.8, 45.4]% at PEEP 5 cm H2O, P = 0.078), as the reduction in shunt was accompanied by a significant increase in dead space; in prone position, PEEP 15 cm H2O significantly worsened V/Q mismatch (35.9 [28.3, 43.4]% at PEEP 15 cm H2O vs. 31.7 [24.3, 37.6]% at PEEP 5 cm H2O, P < 0.001), as it failed to reduce shunt while significantly increasing dead space.
Conclusions:
In patients with higher R/I ratio, PEEP 15 cm H2O improved V/Q mismatch in both supine and positions. In patients with lower R/I ratio, PEEP 15 cm H2O did not impact V/Q mismatch in supine position but significantly worsened it in prone position.
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