Page 957 - Small Animal Internal Medicine, 6th Edition

CHAPTER 53 Electrolyte Imbalances 929

necessary to prevent the recurrence of clinical signs. An IV cat, although reference ranges may vary between laborato-
continuous-rate infusion (CRI) of calcium, in addition to ries. Young dogs (<12 months) especially of large and giant
VetBooks.ir oral calcium, vitamin D, or both, is recommended for breeds and young cats (<6 months) have higher serum phos-
phorus concentrations than adults, which should gradually
animals with disorders causing prolonged severe hypocalce-
mia (e.g., primary hypoparathyroidism, postparathyroidec-
ranges) by 12 months of age. Bone growth and an increase
tomy for primary hyperparathyroidism). For IV CRI, calcium decrease to adult values (e.g., typical laboratory reference
gluconate should be administered at an initial dosage of 60 in renal tubular reabsorption of phosphorus mediated by
to 90 mg of elemental calcium/kg/day. Ten milliliters of 10% growth hormone are believed to contribute to this age effect.
calcium gluconate provides 93 mg of elemental calcium. Hyperphosphatemia can result from increased intestinal
Approximately 1, 2, or 3 mg/kg/h elemental calcium is pro- phosphorus absorption, decreased phosphorus excretion in
vided when 10, 20, or 30 mL of 10% calcium gluconate, the urine, or a shift in phosphorus from the intracellular to
respectively, is added to 250 mL of fluids and administered the extracellular compartment. Translocation of phosphorus
at a maintenance rate of 60 mL/kg/day (2.5 mL/kg/h). between intracellular and extracellular compartments is
Calcium salts should not be added to fluids that contain similar to that of potassium. The most common cause of
lactate, acetate, bicarbonate, or phosphates because calcium hyperphosphatemia in dogs and cats is decreased renal
salt precipitates can result. The serum calcium concentration excretion secondary to kidney disease (Box 53.8).
should be monitored every 8 to 12 hours and the calcium
infusion adjusted accordingly with the goal of gradually BOX 53.8
decreasing and then discontinuing the infusion once the
serum total calcium concentration is consistently greater Causes of Hyperphosphatemia in Dogs and Cats
than 8 mg/dL, or the serum ionized calcium concentration Physiologic Causes
is greater than 0.9 mmol/L.
Long-term maintenance therapy may be necessary to Young growing animal*
control hypocalcemia. It is most commonly required for the Increased Input
control of primary hypoparathyroidism and hypoparathy- Hypervitaminosis D*
roidism after bilateral thyroidectomy in cats with hyperthy- Excess supplementation
roidism. Oral vitamin D administration is the primary mode Cholecalciferol rodenticides
of treatment for the management of chronic hypocalcemia Jasmine toxicity
(see Box 53.7). Vitamin D works by stimulating intestinal Excess dietary intake
calcium and phosphorus absorption and, together with para- Osteolytic bone lesions (neoplasia)
thyroid hormone, by mobilizing calcium and phosphorus
from bone. Oral calcium supplements are needed early in Decreased Loss
maintenance therapy in addition to vitamin D. Acute or chronic kidney disease*
The aim of maintenance therapy is to keep the serum Uroabdomen
calcium concentration between 9 and 10 mg/dL (dog) and Hypoparathyroidism*
Hyperthyroidism
between 8 and 9 mg/dL (cat), which controls clinical signs, Hyperadrenocorticism
lessens the risk of hypercalcemia, and provides some stimu- Acromegaly
lus for remaining or ectopic parathyroid tissue to become
functional. The serum calcium concentration should be Transcellular Shifts (ICF to ECF)
monitored closely (initially q24-48h) and adjustments in Metabolic acidosis
therapy made accordingly. Vitamin D therapy is required Tumor cell lysis syndrome
permanently in animals with primary hypoparathyroidism Tissue trauma or rhabdomyolysis
and in animals that have undergone total parathyroidectomy. Hemolysis
Vitamin D therapy usually can be tapered and discontinued Iatrogenic Causes
if only partial or transient parathyroid damage has occurred.
Regardless, calcium supplementation often may be tapered IV phosphorus administration
Phosphate-containing enemas
and stopped. (See Chapter 47 for more information on the Diuretics: furosemide and hydrochlorothiazides
treatment of hypocalcemia.) Appropriate use and selection
of diets to support gestation and lactation are critical for Laboratory Error
optimizing successful reproduction in cats and dogs and to Lipemia
help prevent and treat calcium imbalances. Hyperproteinemia

HYPERPHOSPHATEMIA ECF, Extracellular fluid; ICF, intracellular fluid; IV, intravenous.
*Common causes.
Etiology Modified from DiBartola SD, Willard MD: Disorders of phosphorus:
hypophosphatemia and hyperphosphatemia. In DiBartola SP,
Hyperphosphatemia is present when the serum phosphorus editor: Fluid, electrolyte, and acid-base disorders in small animal
concentration is greater than 6.0 mg/dL in the adult dog and practice, ed 4, St Louis, 2012, Saunders Elsevier.