End-expiratory esophageal pressure versus lower inflection point in acute lung injury

Introduction

No recommendations available concerning protocols of static PV loop and esophageal pressure measurements use set positive end-expiratory pressure (PEEP). The aim of the study was evaluation of the significance of the lower inflection point (LIP) and esophageal pressure monitoring for PEEP adjustment in ALI and ARDS.

Methods

A prospective study performed in one general ICU. We include 72 patients who received mechanical ventilation before evaluation and met ARDS criteria by AECC (1994) - acute onset, PaO₂/FiO₂ lower than 250 Torr, bilateral infiltrates on chest X-ray. Exclusion criteria were age <15 years and pregnancy. We drew a static pressure-volume loop with sustained inflation 40×30 (PV loop) for all patients using a lowflow technique (Hamilton G5) and measured the esophageal pressure (Avea) in 36 of 72 patients. After that PEEP was set according to zero end-expiratory transpulmonary pressure. We compare PV loop data with esophageal pressure measurements.

Results

The low inflection point median was 8 (95% CI = 5 to 10.5) mbar, which does not correspond to the empirically set optimal PEEP of 13 (95% CI = 12 to 15) mbar (P < 0.001, Wilcoxon test). End-expiratory esophageal pressure (EEEP) median was 14 (95% CI = 12 to 18) mbar, the correlation between LIP and EEEP was poor (ρ = 0.279, P = 0.049). We find significant correlation between static compliance and EEEP (ρ = -0.421, P = 0.005). Sustained inflation did not lead to improved oxygenation (P > 0.05). PEEP adjustment by EEEP led to an increase in PaO₂/FiO₂ - median 107 mmHg (95% CI = 18 to 147, P < 0.001). EEEP was similar to empirically set PEEP (P > 0.05).

Conclusion

LIP has poor correlation with EEEP. PEEP adjustment by esophageal pressure was close to empirically set PEEP and can improve oxygenation.