['The aim of this study was to evaluate a postural change test during sinus ultrasound, compared with CT scan, in case of partial sinusogram to differentiate air-fluid level from mucosal thickening.', 'Prospective clinical investigation.', 'Medical intensive care unit.', '150 intubated patients.', 'Patients were examined by sinus ultrasound in half-sitting position. A partial sinusogram was defined as the sole visualization of the hyperechogenic posterior wall of the sinus. In this situation, a postural change was performed and ultrasound was achieved in supine position. If the partial sinusogram disappeared when the patient was placed in a supine position (positive test), the partial sinusogram was an air-fluid level. If the partial sinusogram did not disappear (negative test), we considered it as a mucosal thickening. The CT and ultrasound were performed on the same day. Radiological maxillary sinusitis (RMS) on CT was defined as the presence of an air-fluid level. Absence of RMS on CT was defined as normal sinus or as the presence of mucosal thickening.', '300 sinuses were examined. A partial sinusogram was found in 90 sinuses and CT scan confirmed the presence of RMS in 55 sinuses (61%). Sensitivity, specificity, positive predictive value, and negative predictive value of postural change test compared with CT were, respectively, 94.6, 85.6, 91.2 and 90.9%. The positive predictive value increased from 61 to 91.2% after the postural change test.'] Does a postural change test improve the prediction of a radiological maxillary sinusitis by ultrasonography in mechanically ventilated patients?