Page 322 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Mixed Acid-Base Disorders 313

and development of a high-AG acidosis. Severe canine hyperchloremic acidosis, fluid therapy will induce a mixed
babesiosis caused by B. canis rossi also has been shown hyperchloremic metabolic acidosis. Parenteral nutrition
to cause this combination of disturbances. 30 The treat- in patients with diarrhea also could cause a mixed
ment in mixed hyperchloremic and high-AG acidoses hyperchloremic acidosis because of the addition of cat-
should be directed at the primary disorders responsible ionic amino acids (e.g., lysine HCl, arginine HCl). Treat-
for metabolic acidosis. Treatment with NaHCO 3 may ment should be directed toward resolving the primary
be necessary in selected patients with low pH and severe disease responsible for the acidosis. Treatment with
corrected hyperchloremia or renal failure. Limitations of NaHCO 3 is safer in hyperchloremic acidoses and should

NaHCO 3 treatment for lactic acidosis were discussed ear- be used if the pH is less than 7.10 or the [HCO 3 ] is less
lier. Sodium bicarbonate is not indicated in diabetic than 10 mEq/L. The potential causes of mixed metabolic
patients even if the pH is less than 7.0. 43,55 disorders are summarized in Box 12-7.

Mixed High-AG Metabolic Acidosis TRIPLE DISORDERS
Two different causes of high-AG metabolic acidosis may Metabolic Acidosis, Metabolic Alkalosis, and
coexist in the same patient, and this usually is a result of Respiratory Acidosis or Alkalosis
lactic or uremic acidosis superimposed on another cause
Triple disorders occur whenever a respiratory disturbance
of high-AG acidosis. The pH and [HCO 3 ] are low in

complicates a mixed metabolic acidosis and metabolic
affected patients with increased unmeasured ions and
alkalosis. The pH and [HCO 3 ] may be normal,

normal chloride gap (see Table 12-4). It is not possible
decreased, or increased, and PCO 2 is higher than expected
to differentiate between simple and mixed high-AG met-
when the mixed metabolic disturbance is complicated by
abolic acidosis if only blood gases and serum electrolytes
are assessed. Serum creatinine concentration, blood urea respiratory acidosis and lower than expected when it is
nitrogen (BUN), and plasma lactate concentration must complicated by respiratory alkalosis. Patients with low-
be measured to confirm the presence of this mixed output heart failure treated with diuretics may develop
disorder. 40 lactic acidosis and hypochloremic alkalosis. If such a
Patients with ketoacidosis may develop lactic acidosis patient develops interstitial pulmonary edema, there is a
decrease in compliance, and stimulation of ventilation
because of decreased tissue perfusion or impaired lactate
causes PCO 2 to decrease and respiratory alkalosis to
use caused by decreased insulin activity. In this circum- 1
develop. With increasing severity of the edema,
stance, lactic acidosis promotes conversion of 1
hypoventilation with respiratory acidosis may occur.
acetoacetate to b-hydroxybutyrate, which does not react
However, dogs have good collateral ventilation, and
with nitroprusside in the urinalysis dipstrip reagent pad, 57
thereby masking the ketoacidosis. 40 It has been suggested hypercapniaoccursonly infulminantpulmonaryedema.
that adding a few drops of hydrogen peroxide to the Patients with gastric dilatation-volvulus can have met-
29,37,61
urine specimen would nonenzymatically convert abolic alkalosis and lactic acidosis. These patients
b-hydroxybutyrate to acetoacetate, which then would also can develop respiratory alkalosis as a result of a
2
37
be detected by the nitroprusside reagent. 41 However, this pain-induced increase in ventilation or sepsis. Respira-
tory acidosis also can develop if ventilation is impaired by
method has been shown to be ineffective in converting 37
b-hydroxybutyrate to acetoacetate in dogs. 10 a grossly overdistended stomach. Severe babesiosis in
dogs infected with B. canis rossi also can cause triple
Treatment in this mixed disorder should be directed
disorders with respiratory alkalosis as a result of a systemic
toward resolving the primary disorder causing metabolic
inflammatory response syndrome (in a sepsis-like state),
acidosis and toward stabilizing the patient. The use and 30
lactic acidosis, and hyperchloremic acidosis. It is not
limitations of NaHCO 3 in lactic acidosis, uremic acidosis,
known why dogs with this disease develop
and ketoacidosis have been discussed previously. Patients
hyperchloremic acidosis. Other potential causes of triple
with severe acidosis (pH, <7.1) and renal failure may
benefit from small, titrated doses of NaHCO 3 . disorders are outlined in Box 12-8. The treatment of tri-
ple disorders should be directed at stabilizing the
Mixed Hyperchloremic Metabolic Acidosis patient’s clinical condition and resolving the underlying
disease process. In the majority of these cases, the meta-
This is a very rare disorder in veterinary medicine because
bolic acidosis is caused by lactic acid accumulation.
the only clinical situation that commonly causes
Therefore the principles discussed under mixed respira-
hyperchloremic acidosis is diarrhea. The pH and
tory acidosis with lactic acidosis are valid here.

[HCO 3 ] are decreased in these patients, and the
AG is normal with corrected hyperchloremia (see
Table 12-4). Fluid therapy with lactated Ringer’s solution TREATMENT
or 0.9% NaCl solution with or without KCl supplemen-
tation is a common cause of hyperchloremic acidosis in When treating a patient with a mixed disorder, always pri-
hospitalized patients. In patients with a preexisting oritize the order in which the abnormalities are managed: