[Significance of static pressure-volume loop and lung computed tomography for differential diagnostics of parenchymal respiratory insufficiency].

UNLABELLED: Purpose of the study was to determine a significance of static pressure-volume loop and lung computed tomography for differential diagnostics of parenchymal lung failure developing during mechanical ventilation.

MATERIALS AND METHODS: 75 patients (42 males and 33 females) with acute lung failure due to parenchymal lung injury during mechanical ventilation were included in to the research. Criteria of including into the research were age over 15, ARDS symptoms absence before respiratory support beginning and modified American-European Consensus Conference ARDS criteria presence during mechanical ventilation (AECC ARDS criteria, 1994--PaO2/FiO2 < 250 mmHg). Lung computed tomography (CT), static compliance and plateau measurement were performed in all patients. Static pressure-volume loop was plotted in 23 patients.

RESULTS: diffuse alveolar damage was diagnosed by CT in 24.3% of patients and "wet sponge" symptom in 10.7% of patients. Dorsal atelectasis (77.3%) and ventilator-associated pneumonia (VAP) (82.7%) were diagnosed in most of patients with AECC ARDS criteria. Sensitivity and specificity of PaO2/FiO2 ratio were too low for diagnostics of ARDS (AUROC 0.67) Patients with diffuse alveolar damage had plateau pressure 25 mbar (95% CI 22-32), while patients with local lung injury (VAP or atelectasis) had significantly lower plateau pressure--20 mbar (95% CI 18-22) (p = 0.014). Elevation of plateau pressure over 30 mbar predicted diffuse alveolar damage with specificity of 100%. Lower inflection point values on the static pressure-volume loop was higher in patients with diffuse alveolar damage than in patients with local lung injury--12 mbar (95% CI 7-17) vs. 6 mbar (95% CI 5-10), (p = 0.042, n = 23). Effective (linear) compliance had poor prognostic value for differential diagnostics of acute respiratory failure due to parenchimal lung injury (p = 0.023).

CONCLUSION: Lung CT plays leading role in differential diagnostics of parenchymal lung failure developing during mechanical ventilation. In the luck of CT scan elevation of plateau pressure over 30 mbar and values of lower inflection point on the static pressure-volume loop over 12 mbar can predict ARDS.