Critical evaluation of methods for determination of blood volume in the dog.

Abstract

In 7 mongrel dogs a total of 202 measurements of blood volume were performed according to three different methods (RIHSA, Cr51, double-isotope method). Careful weighing of tracers and samples proved to be essential for correct measurements. Large vessel hematocrit values obtained by centrifugation and by the distribution of RIHSA in whole blood and in plasma were essentially equal. The disappearance rate of RIHSA averaged 10% per hour, while that of Cr51 differed significantly between dogs with and without saline infusion (20.9 and 13.7% per hour respectively). Values of blood volume for the fasting conscious dog averaged 80 ml/kg of BW with no significant difference between the three methods of determination. The correlation between blood volumes obtained by synchronized determination with Cr51 and RIHSA was rather weak (r=0.7143, standard deviation of the mean error ±14.3%). In agreement with this, the rate offcells showed a large scatter of ±7 and ±10% respectively for the two groups. It was demonstrated that the decrease of activity of Cr51 in the circulating blood due to the uptake of tagged red cells by the spleen is not linear, as initially supposed, but follows an exponential function, resulting in an error in the measurement of red cell volume of +10 and +13% respectively.