Lung ultrasound for detection of pulmonary edema in the critically ill

Abstract

Background For detection and monitoring of pulmonary edema and for guidance in fluid management, chest x-ray (CXR) and thermodilution technique (PiCCO®) is commonly used in the critically ill. Lung ultrasound (LUS) is a cheap and easy method for detection of pulmonary pathology with increasing popularity in emergency departments and intensive care units (ICUs). LUS can be used to detect b-lines as a sign of interstitial lung fluid. Aim The primary goal of this study was to investigate if a simplified 8-zone LUS-protocol would correlate to extravascular lung water in patients with critical illness. A secondary goal was to compare LUS-accuracy in detection of pulmonary edema to chest x-ray. Method A prospective observational pilot study was conducted. Patients with a PiCCO® catheter and/or having a chest x-ray were enrolled and LUS scans performed at the central intensive care unit (CIVA) at Sahlgrenska university hospital. Following an 8-zone protocol, b-line score (BLS) was correlated to extravascular lung water index (EVLWI) obtained through transpulmonary 3 thermodilution. CXR reports were examined for signs of pulmonary edema and compared to BLS. Results 28 patients were enrolled, and 48 lung ultrasound scans performed. LUS compared to transpulmonary thermodilution showed a significant correlation between BLS and EVLWI (r=0.43, p=0.032). In patients with several measurements, there was a positive correlation between changes in BLS and changes in extravascular lung water (p=0.012). The best cut-off value for detection of pulmonary edema was a b-line score of 6. Sensitivity for detection of pulmonary edema using transpulmonary thermodilution was 78% and specificity 64% with an AUC of 0.82. The sensitivity and specificity of b-line score for detection of pulmonary edema using chest x-ray was 100% and 35%. Conclusions In this study of patients with critical illness examined with lung ultrasound, the main finding was that b-line score correlated to extravascular lung water measured with PiCCO®. Compared to chest x-ray, LUS could exclude pulmonary edema. Lung ultrasound is a simple and feasible method. It has a steep learning curve and can be used in emergency departments and intensive care units for detection and monitoring of pulmonary edema.