Page 167 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Disorders of Calcium: Hypercalcemia and Hypocalcemia 157

BOX 6-3 General Treatment of severe clinical signs attributable to hypercalcemia. Addi-
tional expansion of ECF volume with parenteral fluids
Hypercalcemia is then indicated, but sufficient fluid for rehydration
and volume expansion is often provided simultaneously.
Definitive Fluid therapy alone may be sufficient in some animals
Remove underlying cause to reduce the magnitude of hypercalcemia adequately
when the initial serum calcium concentration is less than
Supportive
Initial considerations 14 mg/dL, but often other treatments must be added.
Normocalcemia may be restored by fluid therapy alone
Fluids (0.9% sodium chloride)
if hypercalcemia was initially mild (12 to 13 mg/dL).
Furosemide
Physiologic saline (0.9% NaCl) is the solution of
Calcitonin
choice for correction of the intravascular volume deficit
Secondary considerations and for further slight volume expansion. Slight volume
Glucorticosteroids expansion with 0.9% NaCl promotes calcium loss in urine
Bisphosphonates
secondary to increased GFR and increased filtered load of
Tertiary considerations calcium, and competition from the additional sodium
Sodium bicarbonate ions results in reduced renal tubular calcium reabsorption
Mithramycin (severe toxicity) and enhanced calciuresis. Eleven dogs with hypercalcemia
Ethylenediamine tetra-acetic acid (EDTA) (most with malignancy and one each with primary hyper-
(severe toxicity) parathyroidism and hypervitaminosis D) were treated for
Dialysis 24 hours with IV 0.9% NaCl at 60 mL/kg. A decrease in
Future considerations serum tCa was observed in 7 of 11 dogs (1.3 mg/dL
Calcium channel blockers mean; 0.5 to 2.8 mg/dL), no change in 1 of 11, and
Somatostatin congeners an increase in 3 out of 11 (0.6 mg/dL mean; 0.1 to
Calcium receptor agonists 0.7 mg/dL). Overall there was a decrease in mean serum
Nonhypercalcemic calcitriol analogues tCa of 0.7 mg/dL, but tCa concentration did not return
to the reference range in any dog. 487
ECF volume expansion with lactated Ringer’s solution
a shift of intravascular calcium to other body (6 mg/dL calcium) in dogs results in decreased total pro-
compartments, promoting extrarenal calcium loss, reduc- tein, tCa, and iCa concentrations. Decreases in tCa con-
ing calcium transport across the gut, or some combination centration were greater (12.4%) than those observed for
of these effects. 113,315,354 iCa concentration (3.5%). 468 Thus, volume expansion
with solutions that contain some calcium can be beneficial
Initial Considerations for Treatment because the dilutional effect supersedes the effect of the
Parenteral fluids, furosemide, sodium bicarbonate, additional calcium that is administered. However, physi-
glucocorticoids, or combinations of these treatments ologic saline (0.9% NaCl) is preferred because it is devoid
effectively reduce serum calcium concentrations in most of additional calcium and contains more sodium than that
animals. Repeatable serum hypercalcemia should be con- in lactated Ringer’s solution (154 versus 130 mEq/L).
firmed before prescribing aggressive treatments. It is not Consequently, 0.9% NaCl results in a more rapid reduc-
necessary to reduce serum calcium concentration to tion in serum calcium concentration. An initial fluid vol-
within normal limits, but substantial resolution of serious ume of two to three times maintenance needs (120 to
clinical signs may occur when serum tCa concentration 180 mL/kg/day) usually corrects dehydration, provides
decreases by as little as 1 to 3 mg/dL. maintenance needs, and results in mild volume expan-
sion. The use of sodium phosphate is not recommended
Fluid Therapy because of the potential detrimental effects of soft tissue
Parenteral fluid therapy is an important first treatment for mineralization. 184
all animals with hypercalcemia. The first goal of fluid ther-
apy is to correct dehydration because hemoconcentration Diuretics (Calciuretics)
contributes to increased serum calcium concentration. In Administration of furosemide follows rehydration and
addition, the kidneys respond during ECF volume con- fluid volume expansion as second in importance for treat-
traction with more avid reabsorption of sodium and cal- ment of persistent hypercalcemia. Furosemide promotes
cium from the glomerular ultrafiltrate. Correction of enhanced urinary calcium loss, but calciuresis does not
dehydration abrogates this effect and allows calciuresis follow the use of all diuretics. In particular, thiazides
and natriuresis to occur. should not be used because they may result in
Dehydration should be corrected with intravenous hypocalciuria and potentially may aggravate hypercalce-
fluids within 4 to 6 hours of presentation in animals with mia. Pivotal work was performed in dogs that provide