Computer-Aided Quantitative Ultrasonography for Detection of Pulmonary Edema in Mechanically Ventilated Cardiac Surgery Patients

Background Lung ultrasonography (LUS) has been used for noninvasive detection of pulmonary edema. Semiquantitative LUS visual scores (visual LUS [V-LUS]) based on B lines are moderately correlated with pulmonary capillary wedge pressure (PCWP) and extravascular lung water (EVLW). A new computer-aided quantitative LUS (Q-LUS) analysis has been recently proposed. This study investigated whether Q-LUS better correlates with PCWP and EVLW than V-LUS and to what extent positive end-expiratory pressure (PEEP) affects the assessment of pulmonary edema by Q-LUS or V-LUS. Methods Forty-eight mechanically ventilated patients with PEEP of 5 or 10 cm H2O and monitored by PCWP (n = 28) or EVLW (n = 20) were studied. Results PCWP was significantly and strongly correlated with Q-LUS gray (Gy) unit value (r2 = 0.70) but weakly correlated with V-LUS B-line score (r2 = 0.20). EVLW was significantly and more strongly correlated with Q-LUS Gy unit mean value (r2 = 0.68) than with V-LUS B-line score (r2 = 0.34). Q-LUS showed a better diagnostic accuracy than V-LUS for the detection of PCWP >18 mm Hg or EVLW ≥ 10 mL/kg. With 5-cm H2O PEEP, the correlations with PCWP or EVLW were stronger for Q-LUS than V-LUS. With 10-cm H2O PEEP, the correlations with PCWP or EVLW were still significant for Q-LUS but insignificant for V-LUS. Interobserver reproducibility was better for Q-LUS than V-LUS. Conclusions Both V-LUS and Q-LUS are acceptable indicators of pulmonary edema in mechanically ventilated patients. However, at high PEEP only Q-LUS provides data that are significantly correlated with PCWP and EVLW. Computer-aided Q-LUS has the advantages of being not only independent of operator perception but also of PEEP.