Abstract
Background and Aims
In hemodialysis therapy, intravascular fluid is removed first. As intravascular water is removed, the circulating serum protein concentrations increase, resulting in a marked increase in the driving force which pulls water from the extravascular space into the blood vessels, by a process called plasma refilling. We examined the effect of total fluid removal and intravascular fluid removal as estimated by the change of the hematocrit value during dialysis on the rate of change of the inferior vena cava (IVC) diameter, early diastolic mitral valve inflow (E wave), and lung echo B-lines.
Method
We enrolled 59 patients under maintenance hemodialysis for this study. Lung ultrasound was performed at the first session of the week. Bilateral scanning of the anterior and lateral chest walls was performed with the patient in a supine position. The chest wall was divided into 8 areas (2 anterior and 2 lateral areas per side), and 1 scan was obtained for each area. The total number of B-lines was estimated. Echocardiographic measurements were obtained at the same time and the IVC dimensions and E wave were estimated. We performed each ultrasound examinations at two time-points (just after the start and just before the end of the hemodialysis therapy). We then investigated the rate of change ((post-pre)/post) of the IVC diameter, E wave, and number of B-lines. A peripheral blood sample was obtained before and after the hemodialysis session and the hematocrit was measured. We estimated the intravascular fluid volume as pre body weight /13, and estimated intravascular fluid removal as (post hematocrit – pre hematocrit)/post hematocrit x estimated intravascular fluid. We also defined estimated extravascular fluid removal as total fluid removal – estimated intravascular fluid removal. We investigated the relationship between the total, intravascular and extravascular fluid removals and the rate of change of the IVC diameter, E wave, and number of B-lines.
Results
The rate of change of the IVC diameter was negatively related to the estimated intravascular fluid volume (r=-0.285, P=0.033), but not to the estimated extravascular fluid or total fluid removal. The rate of change of the E wave was negatively related to the estimated intravascular fluid volume (r=-0.422, P=0.001), and the estimated extravascular fluid (r=-0.369, P=0.006) and total fluid removal (r=-0.419, P=0.002). Among these, the rate of change of the E wave was most closely related to the estimated intravascular fluid volume. The rate of change of the number of B-lines was not associated with the estimated intravascular fluid volume, but was negatively correlated with the estimated extravascular fluid (r=-0.368, P=0.005) and total fluid removal (r=-0.353, P=0.008). The estimated extravascular fluid removal was the most closely related to the rate of change of the number of B-lines.
Conclusion
The rates of changes of the IVC diameter and E wave were strongly associated with the estimated intravascular fluid removal, whereas the rate of change of the number of B-lines was correlated with estimated extravascular fluid removal. The E wave represents the flow to the left ventricle, which occurs after left ventricular diastole, reflecting the preload status. The IVC dimensions are strongly associated with the right atrial pressure and blood volume and therefore reflect the intravascular volume. Therefore, both the E wave and the IVC diameter may represent the intravascular fluid volume. On the other hand, the number of B-lines has been reported to be correlated with the amount of extravascular lung water. Our results were consistent with these reports.
The rapidly adapting receptors in mammalian airways and their responses to changes in extravascular fluid volume