Page 719 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

706 SPECIAL THERAPY

conversion of ethylene glycol,and their efficacy relieson the A second treatment is provided if delivery is incomplete
potential for renal elimination of both the toxin and its during the first session or if there is a rebound in ethylene
metabolites. glycol after treatment. Vascular access with a temporary
The goals for hemodialysis are to eliminate the ethyl- dialysis catheter generally provides adequate blood flow.
ene glycol and its metabolites from the animal as quickly The highest efficiency hemodialyzer compatible with
as possible and to correct the accompanying fluid, elec- the extracorporeal volume requirement of the animal
trolyte, and acid-base disturbances and attending uremia. should be used to maximize diffusive removal of the
For suspected poisonings, hemodialysis should be toxins. Blood flow rates between 15 and 25 mL/kg/
initiated immediately to ensure rapid elimination of the min or faster are tolerated. A standard dialysate flow
toxin regardless of previous administration of antidotal between 500 and 600 mL/min is used but can be
therapy or the absence of clinical signs. If the animal increased if the blood flow rate is greater than
needs to be transported, an initial dose of ethanol or 4- 300 mL/min. A dialysate formulated with 3 or
methylpyrazole should be administered, and existing 4 mmol/L potassium, 30 to 35 mmol/L bicarbonate,
dehydration and metabolic acidosis should be and a physiologic sodium concentration is appropriate
corrected. 38,173 It generally is possible to eliminate 90% unless specific electrolyte, acid-base, or hemodynamic
to 95% or more of the toxin with a single intensive dialysis disorders are present. A neutral sodium phosphate addi-
treatment (Figure 29-14). 34,35,137 However, the neces- tive should be added to the dialysate for nonuremic
sary amount of dialysis to deliver when toxicologic results animals to prevent hypophosphatemia (see previous
are unavailable to confirm toxin removal during the treat- Dialysate Additives section). Ethanol should be added
ment is problematic. Urea (MW, 60 Da) is similar in to the dialysate concentrate to achieve a dialysate ethanol
molecular size and distribution volume to ethylene glycol concentration of approximately 0.1% in an effort to
(MW, 62 Da) and can serve as an index for changes in eth- inhibit ongoing metabolism of ethylene glycol to its toxic
ylene glycol clearance similar to its surrogate role for metabolites during the extended hours of dialysis (see
removal of small-molecular-weight uremic toxins. The previous Dialysate Additives section). Ultrafiltration can
URR can be used to predict ethylene glycol reduction be used to correct pulmonary edema or congestive heart
and the dialyzed blood volume required to achieve the failure secondary to the toxin or fluid administration.
removal goal (Figure 29-14). 34,137 To achieve a 90% eth- However, ultrafiltration is minimally effective for
ylene glycol reduction during the course of treatment, it is pulmonary effusions arising from respiratory distress
necessary to select treatment parameters that would syndrome or uremic pneumonitis associated with
promote the same URR for that patient. antifreeze poisoning.
For nonazotemic animals, 90% to 100% of the toxin In uremic animals, the goals for aggressive toxin
should be removed during the first dialysis treatment. removal are constrained by requirements to prevent dial-
ysis disequilibrium syndrome, and dialysis must be deliv-
ered carefully to accommodate all of the patient’s needs.
1.0
A temporary hemodialysis catheter generally is placed to
expedite the initial treatment, but it is replaced with a per-
manent tunneled catheter after 2 weeks if additional dial-
0.8
ysis is required. If the BUN concentration is less than
Reduction ratio 0.5 animals is suitable. For animals with BUN concentrations
125 mg/dL, an intensive treatment as used in nonuremic
greater than 150 mg/dL, the dialysis prescription should
target a 90% to 100% ethylene glycol reduction, but it
must be delivered with a slow, extended treatment tai-
0.3
lored to the hourly URR targets appropriate for the
degree of azotemia (see Table 29-2). For severely uremic
animals, safe urea reduction and greater toxin removal is
0.0
Ethylene Urea Glycolic Ethylene Urea Glycolic achieved when dialysis is provided over 6 to 10 hours. The
glycol acid glycol acid remainder of the dialysis prescription should be
formulated to specific complications accompanying the
Azotemic Nonazotemic
Figure 29-14 Box and whisker plots demonstrating the uremia, fluid volume status, acid-base and electrolyte
reduction ratios for ethylene glycol (light boxes), urea (stippled boxes), disturbances, and hemodynamic stability. Ethanol can
and glycolic acid (dark boxes) in azotemic (n ¼ 20) and nonazotemic be added to the dialysate concentrate as described previ-
(n ¼ 6) dogs. These observations demonstrate that both ethylene ously for nonazotemic animals. Mannitol (Mannitol
glycol and glycolic acid have removal kinetics similar to those for Injection USP, Abbott Laboratories, North Chicago,
urea, and urea reduction ratio can serve as a convenient surrogate Ill.) can be administered at 0.5 to 1.0 g/kg intravenously
to predict removal of these toxins with hemodialysis. 45 to 60 minutes after starting dialysis in both mild and