Page 169 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Disorders of Calcium: Hypercalcemia and Hypocalcemia 159

hypercalcemia was created by twice daily SQ injections of more calcium becomes bound to serum proteins, and
PTH to achieve a target serum tCa of 13 to 15 mg/dL. there is increased binding of calcium to bicarbonate. 468
Furosemide at 2.5 to 15 mg/kg was given IM twice daily Decreases in ionized and tCa concentrations after bicar-
for 4 to 7 days, and saline was added to the diet to match bonate infusions have been observed in dogs 380 and
the volume of urinary loss. Diuresis, natriuresis, and cats. 114 Based on studies in normal cats, a slow IV bolus
calciuresis followed furosemide treatment, but there of sodium bicarbonate from 0.5 to 4.0 mEq/kg 114,314
was no change in serum tCa. Calciuresis was eight times results in a 5% to 12% decrease in ionized calcium (0.2
greater with IV furosemide in the acute treatment model to 0.7 mg/dL). This effect is dose dependent and lasts
compared with the chronic treatment model. 120 to 180 minutes. A small component of this effect
Furosemide IV was compared for its effect in normal is from decreases in serum albumin and serum proteins,
6
adult Greyhounds by bolus or CRI. The same total dose as well as increases in serum or plasma pH, which change
was given with intermittent bolus furosemide IVat 3 mg/ the number or affinity of calcium binding sites. Some of
kg at 0 and 4 hours and at 0.66 mg/kg loading dose this effect may also be from increased binding to
followed by 0.66 mg/kg/hr over 8 hours. Urine sodium circulating complexes (HCO 3 ). 114 Too much alkalinity
and calcium losses were greater and urinary potassium loss can promote tissue mineralization during the presence
less when furosemide was given by CRI compared with of hypercalcemia, so this treatment is given to effect for
intermittent bolus. Cacliuresis, based on total milligrams only a very short while. Reduction in serum calcium con-
of calcium excreted, was 1.6 times greater when furose- centration is slight after administration of sodium bicar-
mide was given by CRI compared with an intermittent bonate alone, but the effect increases with larger doses.
bolus. Unfortunately, serum calcium was not measured Sodium bicarbonate infusion is most likely to be helpful
because of technical errors during the study. CRI may be in combination with other treatments.
safer than intermittent bolus treatments with furosemide
due to more continuous delivery of furosemide to Steroids
nephrons with less variability in serum and tubular drug Glucocorticosteroids can contribute to a significant
concentrations achieved. Restlessness was observed in reduction in serum iCa concentration in hypercalcemic
Greyhounds receiving the CRI of furosemide but not animals with lymphoma, apocrine gland adenocarcinoma
for those with the intermittent boluses. This observation of the anal sac, multiple myeloma, thymoma, hypoadre-
has not been made before in humans, dogs, or horses. nocorticism, hypervitaminosis D, hypervitaminosis A,
Whether this is specific to Greyhounds or occurs in other or granulomatous disease, but they have little effect on
breeds of dogs is not known. serum iCa concentration in animals with other causes
It is important to maintain hydration at all times. of hypercalcemia (Box 6-4). Some cats with IHC also
Proper hydration ensures more delivery of furosemide have a substantial decrease in serum iCa concentration
to the proximal tubules where it must be secreted in order after glucocorticoid treatment. Steroids exert their effects
to exert its subsequent effect in the ascending limb of the mainly by reducing bone resorption, decreasing intestinal
loop of Henle. Large magnitude diuresis occurs with the calcium absorption, and increasing renal calcium
bolus followed by high-dose CRI furosemide methods. It excretion. 328
can be challenging to keep up with this magnitude of Cytotoxicity against neoplastic lymphocytes after
diuresis and adequately replace the volume loss with glucocorticoids can result in a dramatic and rapid
enough IV fluids. Ongoing dehydration results in wors- reduction in serum calcium concentration in dogs with
ening of the hypercalcemia from contraction of the ECFV lymphoma. Whenever possible, however, glucocorticoids
and may pose a risk for ischemic renal injury. Lower dose should be withheld from animals for which a diagnosis
regimens are most often employed by clinicians at 1 mg/
kg followed by 1 mg/kg/hour CRI furosemide. Alterna-
tively, furosemide at 2 to 4 mg/kg two to three times BOX 6-4 Steroid-Sensitive
daily can be given IVor IM, but this is less effective in low- Causes of
ering serum calcium. Serum magnesium can decrease Hypercalcemia
substantially during aggressive furosemide induced diure-
sis, so this should be measured and replacement salts Lymphoma or Leukemia
given in IV fluids as needed.
Multiple myeloma
Thymoma
Sodium Bicarbonate Vitamin D toxicity
Infusion of sodium bicarbonate has been advocated for Vitamin A toxicity
acute or crisis management of hypercalcemia, but most Granulomatous disease
often it is mentioned for use in the presence of metabolic Hypoadrenocorticism
acidosis. 6,113,314 Serum iCa concentration is reduced as Idiopathic hypercalcemia in cats
acidosis is corrected or mild alkalosis is created because