URINARY-EXCRETION AS AN INPUT VARIABLE IN VOLUME KINETIC-ANALYSIS OF RINGERS SOLUTION

The disposition of fluid given by i.v. infusion can be studied by fitt ing one-volume and two-volume kinetic models to the fractioned dilutio n of blood haemoglobin and serum albumin concentrations over time. How ever, the two-volume model is sometimes associated with a high standar d error in estimating the size of the secondary (peripheral) body flui d space, V-2. To examine if a fixed elimination rate constant (k(r)) d etermined by urinary excretion can be used to make the model more stab le, we infused Ringer's acetate 25 ml kg(-1) over 30 min in 15 male vo lunteers (mean age 35 yr). A fixed k(r) increased the total residual e rror when curve-fitting was applied according to the one-volume model. The two-volume model was improved when there was a strong within-pati ent covariance between k(r) and V-2 (r(2) less than or equal to -0.98) . The size of V-2 was 10 litre when the fixed and model-generated valu es of k(r) agreed fully.