Creatinine degradation. II: Mathematical model including the effect of extra-renal removal rates

Previous models of the patient-artificial kidney system have neglected the contribution of creatinine degradation as a pathway for creatinine removal. Creatinine degradation can remove significant amounts of creatinine from dialysis patients, and models which neglect this mechanism are susceptible to error in predicting creatinine concentrations. In this study three models of the patient-artificial kidney system have been developed. The single pool model is the easiest to use since it requires a minimum of patient information, but it is the least accurate in predicting creatinine plasma concentrations. A two-pool model predicts experimental data within 5 percent, and appears to be the most useful model from the consideration of ease of use and accuracy. A three-pool model was derived that is suitable for use on a mini-computer or programmable calculator providing the device is capable of inverting a 3 x 3 matrix. The three-pool model predicts the measured plasma concentrations with 0.5 percent. These models provide a means to account for creatinine degradation and accurately predict creatinine concentrations in dialysis patients.