Page 312 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Mixed Acid-Base Disorders 303

BOX 12-2 Examples of Potential Preexisting Disease Process Associated with
Chronic Acid-Base Disorders*

Respiratory Acidosis Liver disease
Large airway obstruction Hyperadrenocorticism
Tracheal collapse Central neurologic diseases
Brachycephalic syndrome
Laryngeal paralysis Metabolic Acidosis
Neuromuscular disease leading to hypoventilation Hyperphosphatemic acidosis
Myasthenia gravis Renal failure
Polyradiculoneuritis Hyperchloremic acidosis
Restrictive extrapulmonary diseases Renal tubular acidosis
Chronic diaphragmatic hernia Renal failure
Intrinsic pulmonary and small airway disease Diarrhea
Chronic bronchitis High-AG acidosis
Asthma Diabetes mellitus
Diffuse metastatic disease Renal failure
Pulmonary fibrosis Metabolic Alkalosis
Respiratory Alkalosis Hypoalbuminemic alkalosis
Hypoxemia Liver failure
Pulmonary fibrosis Protein-losing enteropathy
Right-to-left-shunt Protein-losing nephropathy
Severe anemia Hypochloremic alkalosis
Pulmonary disease without hypoxemia Diuretic therapy
Interstitial lung disease Vomiting of stomach contents
Centrally mediated hyperventilation

*These patients are at higher risk for mixed acid-base disorders.

TABLE 12-1 Primary and Secondary Changes in Simple Acid-Base Disorders
Disorders Primary Change Compensatory Response

Metabolic acidosis #HCO 3 # PCO 2
Metabolic alkalosis " HCO 3 " PCO 2
Respiratory acidosis " PCO 2 " HCO 3
Respiratory alkalosis # PCO 2 # HCO 3

with certainty, and data in dogs have been derived mainly experimentally induced metabolic acidosis consistently
16
from experiments using normal dogs (Table 12-2). show a lack of ventilatory compensation. In one study
Compensatory rules for cats should be used with caution in which cats were chronically fed a diet containing

because values are derived from a limited number of nor- NH 4 Cl, significant decreases in pH and [HCO 3 ]were
9
mal cats with experimentally induced acid-base disorders. observed, but there was no change in PCO 2 . Similar
The reader is referred to Chapters 9, 10, and 11 for results were obtained in another study also adding
further discussion of compensation. NH 4 Cl to the diet 31 and with dietary phosphoric acid
supplementation. 19 Contrary to what happens in dogs
RESPIRATORY COMPENSATION IN and humans, the feline kidney apparently is unable to
METABOLIC PROCESSES adapt to metabolic acidosis and does not increase produc-
Metabolic acidosis is characterized by an increase in tion of ammonia or glucose from glutamine during acido-

[H ], a decrease in serum [HCO 3 ] and blood pH, sis. 31 Based on these studies, cats may not compensate for
þ
and a secondary decrease in PCO 2 as a result of secondary metabolic acidosis to the same extent (if at all) as do dogs
hyperventilation. The expected decrease in PCO 2 in dogs and humans. Thus formulas for dogs or humans should
with metabolic acidosis may be estimated as 0.7 mm Hg not be extrapolated for use in cats. The clinical finding

for each 1-mEq/L decrease in [HCO 3 ]. 16 Cats with of metabolic acidosis and normal PCO 2 in a cat should