Lung ultrasound during hemodialysis: the role in the assessment of volume status
Chest ultrasonography is a useful tool to assess extravascular lung water at bedside. In presence of interstitial-alveolar imbibition, vertical artifacts arising from the pleura are detected; these are called B-lines. Although a positive linear correlation between B-lines and extravascular lung water has been shown in symptomatic heart failure patients, the subclinical phase of pulmonary imbibition and the clearance of B-lines after rapid body fluid removal have been less investigated. The aim of this study was to assess if chest ultrasound could detect lung water imbibition and its variations induced by dialysis, an experimental model of controlled rapid fluid loss. Forty-one patients undergoing hemodialysis were studied. Total number of B-lines from ultrasound chest scanning and vena cava diameters were measured before and after treatment. Before dialysis, most of the patients presented ultrasound signs of pulmonary imbibition despite the absence of dyspnea; the number of B-lines was associated with the accumulated weight before treatment (p < 0.05) as well as with the residual weight after dialysis (p < 0.01); B-lines and end-inspiratory and end-expiratory vena cava diameters were also significantly reduced after dialysis. Moreover, B-lines reduction was significantly related to weight loss. Ultrasound performed at the bedside can detect lung water and intravascular overload and their reduction after dialysis in yet asymptomatic patients. These observations add further evidence regarding the use of lung ultrasound and inferior vena cava measurement in estimating volume overload and monitoring the response to therapy both in hemodialysis and congestive heart failure patients.