Case example 2: A diabetic husky with a fibrosarcoma

Signalment and history: An 8-year-old 44-lb (20-kg) spayed female Siberian husky is a poorly regulated diabetic presenting for surgical excision of a grade I fibrosarcoma on the right thoracic wall. A urine dipstick test was positive for a trace amount of ketones. The results of an arterial blood gas analysis performed after premedication with 0.3 mg intravenous buprenorphine and before anesthetic induction are shown to the left.

Interpretation: The patient has hyperglycemia, hypochloridemia, and a normal pH despite decreased base excess. Oxygenation is within acceptable limits considering the altitude.

This is a case in which further investigation of the patient's metabolic status would be of interest. Abnormal chloride, keto acids, and bicarbonate can all affect the overall metabolic acid-base status. Calculation of the anion gap is as follows:

(Na+ + K+) – (Cl- + HCO3 -) =

(142 + 4.7) – (100 + 18.9) = 27.8 mmol/L

Normal anion gap values in dogs are between 12 and 25 mmol/L, so this dog exhibits a mild increase. Diabetic ketoacidosis is one of several relatively common scenarios associated with an increased anion gap. Since the patient's pH is normal, an offsetting metabolic alkalosis should be considered. In this case, the hypochloridemia would be of interest. However, evaluation of chloride is more complicated, since chloride changes can occur because of changes in body water balance or gain or loss of chloride. To correct for changes in body water, chloride should be corrected by considering changes in sodium.

Cl- corrected = Cl- measured X (Na+ normal/Na+ measured)

= 100 mmol/L X (146 mmol/L / 142 mmol/L)

= 102.8 mmol/L

Normal corrected chloride in dogs is reported as 107 to 113 mmol/L, so this patient has a true hypochloridemia. Hypochloridemia alone would result in a metabolic alkalosis. In this case, it is an offsetting metabolic acid-base disturbance (i.e. two primary metabolic conditions that are opposite in their affect on pH).

Causes of corrected hypochloridemia in dogs include pseudohypochloridemia, vomiting of stomach contents, diuretic therapy, chronic respiratory acidosis, hyperadrenocorticism, exercise, and administration of high-sodium-concentration solutions such as sodium bicarbonate. Additionally, while not commonly reported in dogs, cats with ketoacidosis may have hypochloridemia that may represent a form of compensation or may be due to osmotic diuresis. None of the above are known to have occurred in this patient, but further evaluation may be indicated.1

REFERENCE

1. de Morais HA, Biondo AW. Disorders of chloride: hyperchloridemia and hypochloremia. In: DiBartola SP, ed. Fluid, electrolyte, and acid-base disorders in small animal practice. 3rd ed. St. Louis, Mo: Saunders-Elsevier, 2006.