Page 271 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

262 ACID-BASE DISORDERS

dogs and cats with anuric or oliguric acute renal failure
caused by EG intoxication is unfortunately very poor. 57,227
Salicylate Intoxication
Aspirin (acetylsalicylic acid) is hydrolyzed to salicylic acid
(pK’ a ¼ 3.0) in the liver. Salicylate intoxication is uncom-
mon in small animal practice and is an example of a mixed
acid-base disturbance characterized by metabolic acidosis
and respiratory alkalosis. Salicylate intoxication in
anesthetized, spontaneously breathing dogs resulted in
a mixed respiratory alkalosis and metabolic acidosis. 218
The stimulation of ventilation is caused by a direct
effect of salicylate on the medullary respiratory center.
Salicylate also uncouples oxidative phosphorylation
A in mitochondria, and the associated disturbances in
carbohydrate metabolism lead to metabolic acidosis
characterized by an increased anion gap associated with
accumulation of lactic acid, ketoacids, and other organic
acids. Salicylate usually makes a minor contribution to the
observed increase in unmeasured anions.
Gastric lavage with activated charcoal should be
performed if ingestion occurred less than 6 to 12 hours
before admission. Administration of NaHCO 3 promotes
removal of salicylate from tissues and enhances its urinary
excretion by the mechanism of diffusion trapping. Alka-
linization of ECF and urine increases the proportion of
drug present in the ionized form and thus favors diffusion
of more nonionized salicylic acid from cells into ECF and
urine, where it can be trapped as the poorly diffusible ion-
B ized form. An attempt should be made to maintain urine
pH above 7.5 during alkaline diuresis with NaHCO 3 ,
Figure 10-5 Photomicrographs of (A) calcium oxalate
monohydrate and (B) dihydrate crystals in urine sediment. (From especially if metabolic acidosis is the predominant acid-
Chew DJ, DiBartola SP. Diagnosis and pathophysiology of renal base disturbance. Alkalinization should be carried out
disease. In: Ettinger SJ, editor. Textbook of veterinary internal with caution, if at all, when respiratory alkalosis is the pre-
medicine. Philadelphia: WB Saunders, 1989: 1907.) dominant acid-base disturbance. Glucose infusion is
recommended to prevent reduction in CNS glucose con-
centration. Hypokalemia may develop during treatment
dosage of fomepizole developed mild sedation, but no as a result of NaHCO 3 administration and diuresis, and
biochemical evidence of toxicity was identified. parenteral fluids should be supplemented with potassium
Thiamine promotes conversion of glyoxylate to gly- as needed.
cine, and pyridoxine promotes conversion of glyoxylate
to a-hydroxy-b-ketoadipate (see Fig. 10-4). These Metaldehyde Intoxication
vitamins may be administered to promote alternative
pathways of glyoxylate metabolism, but efficacy has not Metaldehyde is a tetramer of acetaldehyde used as a snail
been demonstrated for such treatment. In one study, all and slug bait that can cause seizures and hyperthermia in
241
nonazotemic dogs treated with fomepizole within 2 to dogs that ingest it. It is hydrolyzed to acetaldehyde in
8.5 hours after EG ingestion survived, whereas only 1 of the stomach, which then is absorbed and metabolized to
acetic acid (pK’a ¼ 4.75). Acidemia was present in 6 of 11
21 azotemic dogs treated 8.5 to 38 hours after ingestion
57 intoxicated dogs in which arterial blood gas analysis was
survived.
Peritoneal dialysis or hemodialysis is necessary if the performed. Three dogs had metabolic acidosis and three
animal has anuric or oliguric renal failure at the time of had mixed acid-base disturbances that were not further
presentation. Early dialysis may also be helpful to remove characterized. Conversion of acetaldehyde to acetic acid
toxic intermediate metabolites. Despite dialysis, affected could explain development of metabolic acidosis, and
dogs may progress to end-stage renal disease and become ventilatory disturbances associated with generalized
dependent on dialysis. The prognosis for survival in adult seizures (either respiratory alkalosis or acidosis) could
have contributed to development of mixed acid-base