Page 697 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

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.