Non-invasive, optical measurement of absolute blood volume in hemodialysis patients

Abstract

During haemodialysis, fluid is removed from, or infused into patients after careful clinical assessment of their hydration states. Unfortunately, these assessments are often imprecise, resulting in either fluid overload or intravascular volume depletion. Since hypovolaemia plays an important role in symptomatic hypotension, which complicates up to 25% of dialysis treatments, there has been increased interest in blood volume (BV) monitoring in recent years. Previous authors have suggested monitoring change in BV during dialysis by examining alterations in optical density, optical reflection, mass density, viscosity, protein concentration or electrical conductivity. However, none of these described methods has measured absolute BV, which is at least as important a determinant of dialysis-related hypotension as the relative change in BV. The best method currently available is measurement of red cell and plasma volumes by dilution of radioactively labelled blood elements. The time-consuming nature of this method and the exposure of the patient to radiation makes it unsuitable for routine clinical use, especially if a number of studies are required.