Role of Lung Ultrasound Imaging and Pulsed-wave Doppler in the Assessment of Lung Consolidations in Mechanically Ventilated Patients.

Ventilator-associated pneumonia has a considerable impact on morbidity and mortality in intensive-care patients. Chest radiography, which is the most frequently used imagery test for bedside lung evaluation in mechanically ventilated patients, is recognized to be poorly sensitive and non-specific for the diagnosis of ventilator-associated pneumonia. Bronchoalveolar lavage using a bronchoscope remains the most reliable tool for the diagnosis of this nosocomial infection. However, a bronchoscopy may not be feasible in all patients and waiting time before final results become available may cause a delay in the initiation of the treatment, thus increasing the risk of mortality. Lung ultrasound is a promising non-invasive, non-radiant, portable and easy to use tool especially in critically-ill patients.

Dependent atelectasis is a frequent phenomenon in mechanically ventilated patients. The presence of clinical infection signs raises the question of the nature of the infiltrate. A consolidation of infectious nature differs from atelectasis by its local hypoxic pulmonary vasoconstriction inhibition. In patients breathing spontaneously, it is possible to detect this difference using the RAcT, measured by pulsed-wave Doppler in an arterial blood vessel located in a pulmonary consolidation visible by ultrasound examination. The use of pulsed-wave Doppler to measure the RAcT in a consolidation added to the value of general lung ultrasound could help determine the infectious or atelectatic nature of a consolidation in mechanically ventilated patients. However, the RAcT has never been studied in patients under positive pressure ventilation. In this observational study, the investigators will explore the role of measuring the RAcT and of general lung ultrasound as a diagnostic tool to detect pneumonia in mechanically ventilated patients.