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684        SPECIAL THERAPY


            QUANTIFICATION OF HEMODIALYSIS                          100
            DELIVERY AND UREA KINETIC
            MODELING
                                                                     80
            The delivery (dose) and efficacy of hemodialysis can be
            expressed in a variety of ways with differing degrees of
            complexity and utility. Predialysis and immediate        60
            postdialysis concentrations of routine serum chemistries  Urea reduction ratio (%)
            (e.g., urea nitrogen, creatinine, phosphorus, bicarbonate,  40
            electrolytes) are the simplest expression of efficacy and
            can be applied similarly to their use in conventional ther-
            apy (Figures 29-1 and 29-2). 48,105,120,172,183  Although  20
            useful to document the instantaneous outcome of the                      N   517 HD treatments in 72 dogs
            treatment, these assessments do not facilitate the uniform                       (2002–2004)
            prescription of dialysis to animals of differing size or met-  0
                                                                       0       1       2       3       4       5
            abolic status. Nor do they help to clarify the excretory
                                                                                 Blood processed (L/kg BW)
            impact of the therapy beyond the intradialytic interval.  Figure 29-3 Prediction of dialysis treatment intensity (urea
            The predialysis and postdialysis concentrations of plasma  reduction ratio [URR]) as a function of the volume of blood
            urea and creatinine can be expressed further as reduction  processed in 72 dogs undergoing hemodialysis. URR was computed
            ratios (URR and CrRR, respectively), which are used rou-  from predialysis and postdialysis BUN concentration (Appendix,
            tinely to evaluate the intensity of therapy (Appendix,  Equation 2). The volume of blood processed (Q b   T d ) was indexed
            Equations 2 and 3).* Urea reduction ratio (URR) can  to body weight to compare dogs of different sizes. The relation
                                                                                    a(Q b   Td/BW)
            be expressed either as the fractional or percent in change  (modeled as URR ¼ 1 e  , r ¼ 0.69) is displayed as a
                                                                                              2
            in urea during the treatment and is the most universally  thick solid line with its 95% confidence interval (CI; thin lines).
            used predictor of adequacy for dialysis sessions in animals  To achieve a low-efficiency treatment with URR equal to 30%, a
                                                                 volume of 0.3 L of blood/kg of body weight must be processed
            (Figures 29-3 and 29-4; Table 29-2). The average dialysis  during the treatment (e.g., 6 L in a 20-kg dog). The variation in
            treatment in cats and most dogs will achieve a URR   resulting URR (95% CI, 15% to 45%) underscores the necessity for
            approaching 95%. This high level of treatment intensity  close monitoring of the delivered (and not prescribed) dose of
                                                                 dialysis for each treatment. Similarly, a URR of 80% is obtained
                                                                 with 1.4 L (95% CI, 0.9 to 2.9) of blood processed per kilogram of
               80                                                body weight (e.g., 28 L in a 20-kg dog).

                                          Kr 0.4 mL/min
               60
                                              Kr 3.0 mL/min         100
              BUN (mg/dl)  40                   Kr 4.5 mL/min        80



                                                                   Urea reduction ratio (%)
               20                                                    60



                0
                      0        2         4        6        8         40
                              Time post-dialysis (days)
            Figure 29-2 Changes in BUN during and after 5 hours of
            hemodialysis treatments in a 33-kg dog presented for acute  20
            antifreeze poisoning at varying degrees of residual urea clearance.       N   271 HD treatments in 66 cats
                                                                                             (2000–2004)
            The predialysis and immediate postdialysis BUN concentrations  0
            reflect a simple assessment of treatment intensity (dose). The eKt/V  0  1            2            3
            (approximately 2.9 per session) for the dialysis treatments was       Blood processed (L/kg BW)
            identical for each level of urea clearance, yet the rate of increase and  Figure 29-4 Prediction of dialysis treatment intensity (urea
            the equilibrated BUN concentration after stopping dialysis increased  reduction ratio [URR]) as a function of the volume of blood
            inversely with residual urea clearance.              processed in 66 cats undergoing hemodialysis. Other conventions
                                                                 are as described for Figure 29-4. The closer correlation (r ¼ 0.85)
                                                                                                          2
                                                                 between volume of blood processed and URR in cats compared with
                                                                 dogs is probably because of the more uniform body shape and sizes
            *References 34, 38, 40, 96, 105, 120, 156.           in this species.
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