QUASI-STEADINESS APPROXIMATION FOR THE 2-COMPARTMENT SOLUTE KINETIC-MODEL

We analytically solved the equation of the Variable volume, two-compar tment solute kinetic model (TCSKM). From the solution, we constructed an expression of weekly concentration profiles developing in the patie nt's body by routine hemodialyses. Obtained formulas can be used to ca lculate Kt/V, solute reduction index (SRI), the solute generation rate (G) per unit distribution volume (V), and a mass transfer coefficient (MTC) between the two compartments. To estimate these parameters, the formulas only need three-point data during a dialysis, that is, pre-, one-hour, and post-dialysis solute concentrations instead of four tha t would otherwise be needed. A 48 hour data point is not required. The weekly concentration profiles can be easily calculated by the formula s. As examples of clinical applications, we calculated Kt/V, G/V, and SRI of urea, Cr, and uric acid using plasma data of 121 hemodialyzed p atients. Then the results were compared with the single-compartment so lute kinetic model (SCSKM). The obtained mean MTC/V values, that is, 1 .08 (1/hr) for urea, 0.53 (1/hr) for Cr, and 1.11 (1/hr) for uric acid , were consistent with the previous works. SCSKM overestimated the mea n G/V by 7.1%, 15.9%, and 10.0%, and the mean SRI by 6.7%, 18.6%, and 10.0%, for urea, Cr, and uric acid, respectively. The solute distribut ion volume ratio of TCSKM to SCSKM, (V)(TCSKM)/(V)(SCSKM), depended on the value of MTC/V and the hemodialysis duration. Using pedometers, w e measured the total number of steps the patients took during a week. We found that the total number of steps in a week was significantly co rrelated with the Cr generation rate (r = 0.285, P < 0.03), but that i t was not significantly correlated with the other generation rates (r = 0.204, P > 0.09 for urea, and r = 0.209, P > 0.08 for uric acid). Th ese data suggest that the Cr generation rate is related to the patient 's physical activity. We conclude that the formulas can estimate an ad equate dialysis prescription for the hemodialyzed patient.