Page 708 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Hemodialysis and Extracorporeal Blood Purification 695

change the serum bicarbonate concentration during to the dialysate concentrate. The amount of phosphate
short treatments at low blood flow rates even with high additive required will vary depending on the proportioning
dialysate bicarbonate concentrations. 58 Under these ratio of the delivery system, but 67 mL (2.2 oz) or 133 mL
conditions, dialysate bicarbonate can be set to (4.5 oz) of Fleet Enema solution per gallon of concentrate
30 mmol/L with little likelihood of neurologic solution produces a dialysate phosphate concentration that
complications. It should be decreased promptly if the ani- is approximately 2 mg/dL or 4 mg/dL, respectively, when
mal shows signs of tachypnea, restlessness, stupor, blind- proportioned at roughly1:40.
ness, or other clinical evidence of impending dialysis Ethyl alcohol is an important additive to bicarbonate-
disequilibrium syndrome. Dialysate bicarbonate concen- based dialysate for the treatment of acute ethylene glycol
tration should be set more cautiously between 20 to or methanol intoxications. 31 Alcohol is added directly to
25 mmol/L for intensive dialytic treatment in animals the acid concentrate in sufficient volume to produce an
with severe metabolic acidosis associated with enriched dialysate with a proportioned concentration of
nonazotemic diseases such as antifreeze intoxication. approximately 0.1% ethanol. 119 The ethanol diffuses
A low dialysate bicarbonate concentration also should from the dialysate into the patient to maintain a constant
be selected for treatment of animals with metabolic or blood alcohol concentration sufficient to competitively
respiratory alkalosis. Inappropriate selection of a high inhibit alcohol dehydrogenase and minimize further
dialysate bicarbonate could worsen the alkalemia. For metabolism of the ethylene glycol while it is being
maintenance hemodialysis treatments, a dialysate bicar- dialyzed from the patient.
bonate concentration of 30 mmol/L will produce a
postdialysis serum bicarbonate concentration of approxi- Dialysate Temperature
mately 23 mmol/L after 4 or 5 hours of dialysis. A dialy- Dialysate temperature is taken for granted as a compo-
sate concentration of 35 to 40 mmol/L yields greater nent of the dialysis prescription but should be regarded
accrual of buffer but often is associated with relentless as a functional contributor to the dialysis session. Dialysis
panting during the treatment. machines manufactured for human patients usually are
configured with an upper dialysate temperature limit at
Dialysate Additions 38 C, which is the lower temperature reference for nor-

Hyperphosphatemia is a common feature of acute and mal dogs and cats. This is the temperature typically pre-
chronic uremia, 35,36,95,131 and for both conditions the scribed for routine dialysis sessions in animals without
dialysate is formulated to contain no phosphate to facili- regard for the benefits or consequences of alternative
tate phosphate removal. The dialysance of phosphate is temperature prescriptions. Most hypothermic patients
more complex than for either urea or creatinine with four will warm to approximately 38 C by the end of the dialy-

contributory pools possibly participating in its sis session. Most animals develop chills with the dialysate
removal. 165 These interactive extracellular, intracellular, temperature set to 38 C because of cooling of the blood

and reserve pools of phosphate are large, in the extracorporeal circuit before it returns to the
compartmentalized, poorly exchangeable with the serum animal. These signs can be controlled with heated
pool, and subject to regulatory control. Consequently, blankets or heat lamps.
the amount of phosphate eliminated during a dialysis Dialysate temperature also influences the hemody-
treatment may be small compared with the overall phos- namic stability of patients during routine dialysis
phate load. 91,115,165 Hyperphosphatemia usually is not treatments and patients predisposed to hypotension
corrected during short and less intensive treatments, during hemodialysis.* Dialysate set to normal body tem-
but it can be normalized or transient hypophosphatemia perature can cause heat accumulation and an increase in
can develop with daily hemodialysis schedules or core bodytemperature. Evensubtleincreasesin bodytem-
34,91,165
treatments longer than 4 or 5 hours. Postdialysis perature can augment the development of hypotension in
hypophosphatemia rebounds rapidly after treatment animals undergoing ultrafiltration. 150 This hemodynamic
without development of clinical signs in uremic animals. response is initiated by cutaneous vasoconstriction
In contrast, persistent hypophosphatemia and the risks of induced by ultrafiltration-associated hypovolemia and
hemolysis, decreased oxygen delivery, or CNS and neuro- decreased dissipation of the accumulated heat. At a critical
muscular disturbances can develop in animals with increase in core body temperature, a thermal homeostatic
normal predialysis serum phosphate concentrations reflex is triggered, causing peripheral vasodilatation,
when dialyzed with a standard (no phosphate) dialysate. decreased peripheral vascular resistance, and symptomatic
For these conditions (i.e., hemodialysis for toxin or hypotension. 103,109,110,140,155 Finite increases in body
fluid removal or well-managed patients with CKD), the temperature can be documented in animals during
dialysate phosphate concentration can be adjusted to routine dialysis treatments with ultrafiltration.
physiologic concentrations by addition of a neutral sodium
phosphate solution (Fleet Enema, Fleet Brand Pharma-
ceuticals, C. B. Fleet Company, Inc., Lynchburg, Va.) *References 30, 102, 103, 109, 110, 150, 155, 176.