Changes in blood parameters during hemodialysis as determined by conductivity measurements

Hypotension is one of the complications frequently seen during hemodialysis. The decrease in intravascular volume caused by ultrafiltration plays an important role in its pathogenesis. A transcellular fluid shift from the extracellular to the intracellular compartment may aggravate this depletion. Continuous recording of blood volume during dialysis would be beneficial in detecting hypovolemia at an early stage. The purpose of this study was to evaluate the use of an electrical conductivity method in detecting hypovolemia and changes in red cell volume. Blood and plasma conductivities were measured, as was hematocrit. Erythrocytes were counted and blood and plasma volume changes were calculated from reciprocal erythrocyte counts. Blood and plasma conductivities were substituted into an equation to calculate hematocrit. Red cell volume (MCV) was calculated from hematocrit and erythrocyte counts. The MCV decreased 3%, and calculated hematocrit corresponded very well with measured hematocrit. Blood and plasma volume decreased by 13.5 and 17.5%, respectively. In summary, it was possible to estimate hematocrit by the conductivity method. The MCV did not change significantly. This method offers the possibility of measuring blood volume on-line.