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Opening pressures and intratidal opening and closing in ARDS lung

Introduction

Intratidal opening/closing is believed to be one of the main triggers of ventilator-induced lung injury; the application of higher PEEP united with the limitation of plateau pressure at 30 cmH2O may limit this phenomenon. We aim to evaluate the intratidal opening/ closing at different PEEP levels and the amount of lung parenchyma that regains inflation going from 30 (pressure limit of tidal ventilation) to 45 cmH2O.

Methods

Patients with ARDS underwent whole-lung low-dose (60 mAs, 120 kV) computed tomography at PEEP 5 cmH2O end expiration and end inspiration, PEEP 15 cmH2O end expiration and end inspiration, and airway pressure 30 and 45 cmH2O end inspiration. Quantitative analysis of CT data was performed and recruitability was defined as the fraction of lung parenchyma that regains inflation going from 5 cmH2O end expiration to 45 cmH2O end inspiration. Patients were classified as high recruiters (HR) and low recruiters (LR) according to the median lung recruitability (14% of lung parenchyma).

Results

Eighteen patients (male 12, age 56.0 ± 18.6 years, BMI 25.6 ± 5.2 kg/m2, PaO2/FiO2 166 ± 70, tidal volume 496 ± 84 ml, RR 19 ± 7.4 breaths/minute, PEEP 11.4 ± 3.7 cmH2O) were enrolled. The fraction of lung parenchyma that could be recruited at plateau pressure above 30 cmH2O was highly variable with a median of 5% (IQ range 1 to 17%) corresponding to a median 16% (IQ range 10 to 47%) of total lung recruitability. Indeed we observed a statistically relevant difference in lung recruitment between airway pressures of 30 and 45 cmH2O (P = 0.016). With PEEP 5 cmH2O, median opening/closing was 129 g (IQ range 124 to 145 g) in the HR group and 50 g (IQ range 24 to 76 g) in LR (P = 0. 006), corresponding to 8% of lung parenchyma (IQ range 6 to 8%) in HR and 4% (2 to 7%) in LR (P = 0.053). Increasing the PEEP level to 15 cmH2O, median opening/closing was 67 g (IQ range 24 to 95 g) in the HR group and 45 g (0 to 80 g) in the LR group (P = 0.512), corresponding to 3% (1 to 5%) in HR and 3% (0 to 5%) in LR (P = 0.93). We observed a statistical difference between recruitments with PEEP 5 and PEEP 15 in the HR group (P = 0.013) but not in the LR group (P = 0.781).

Conclusion

A highly variable and significant fraction of lung parenchyma is always closed with tidal ventilation at 30 cmH2O plateau pressure, regardless of the PEEP level applied; this implies that sigh or periodic recruitment maneuvers may lead to opening and closing. Intratidal opening/closing was reduced but not abolished in all patients while ventilating at higher PEEP level (15 cmH2O).

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Correspondence to I Algieri.

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Algieri, I., Chiumello, D., Cressoni, M. et al. Opening pressures and intratidal opening and closing in ARDS lung. Crit Care 18, P294 (2014). https://doi.org/10.1186/cc13484

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Keywords

  • Lung Injury
  • Airway Pressure
  • Lung Parenchyma
  • Periodic Recruitment
  • Plateau Pressure