Page 951 - Small Animal Internal Medicine, 6th Edition

CHAPTER 53 Electrolyte Imbalances 923

creatinine concentrations, should be considered normal. The
TABLE 53.3 serum total calcium concentration does not fluctuate with
VetBooks.ir Guidelines for Potassium Supplementation in IV Fluids age in cats, but the serum ionized calcium concentration
may be higher (<0.1 mmol/L) in cats younger than 2 years

FLUID INFUSION
Most automated and in-house serum chemistry analyzers
SERUM K TOTAL mEq OF MAXIMUM of age than in older cats.
+
+
(mEq/L) K /L OF FLUIDS RATE (mL/kg/h)* measure the total serum calcium concentration, which con-
sists of biologically active, ionized calcium (55%), protein-
>3.5 20 25 bound calcium (35%), and calcium complexes (10%). A
3.0-3.5 30 16 drawback to this is that alterations in the plasma protein
2.5-3.0 40 12 concentration may alter the total serum calcium concen-
2.0-2.5 60 8 tration, yet the ionized calcium concentration remains
<2.0 80 6 normal. For this reason, serum albumin and total protein
concentrations should be measured when the total serum
*Total hourly potassium administration should not exceed 0.5 mEq/ calcium concentration is determined in the dog. Simple
kg body weight. quantitative changes in albumin and total plasma proteins
do not cause hypocalcemia or hypercalcemia in dogs, even
though total serum calcium levels may appear to be low
of the serum potassium concentration is important during or high on the biochemistry panel. Historically, the follow-
treatment and should initially be done every 6 to 12 hours ing formulas have been used to estimate the total serum
depending on the severity of the hypokalemia and the rate calcium concentration in dogs with hypoalbuminemia or
of potassium administration. Adjustments in potassium hypoproteinemia:
therapy should be made accordingly, with the goal of estab-
(
(
lishing a normal serum potassium concentration and then Adjusted calcium mgdL) = Serum calcium mgdL)
(
.
maintaining the serum potassium concentration in the − Serum albumin gdL)+ 35
normal range as treatment is withdrawn. Clinical signs of
hypokalemia usually resolve within 1 to 5 days after correc- or
tion of hypokalemia.
(
(
Depending on the underlying cause, long-term oral Adjusted calcium mgdL) = Serum calcium mgdL)
04
.
[
potassium supplementation may be required to prevent − (. × Serum tottal protein gdL])+ 33
recurrence of hypokalemia. Potassium gluconate powder or
capsules are commonly used as an oral dietary potassium These formulas are not used in dogs younger than 24
supplement for dogs and cats with minimal gastrointestinal weeks of age, because high values may be obtained, nor are
side effects. The recommended dose is 2.2 mEq of potassium they used in cats, because there is no linear relationship
per 100 calories of required energy intake per day or 2 mEq between serum total calcium and serum albumin and total
of potassium per 4.5 kg of body weight twice a day. Subse- protein concentration in cats. These formulas yield a rough
quent adjustments in dosage are made on the basis of clinical estimate of the total serum calcium concentration and were
response and serum potassium concentrations. Fruits such developed without verification by serum ionized calcium
as kiwi and bananas are also a good source of potassium. Ten measurements. Subsequent studies identified a poor correla-
inches (25 cm) of banana contains approximately 10 mEq of tion between adjusted total calcium results and correspond-
potassium. ing serum ionized calcium concentrations, suggesting that
adjusted total serum calcium concentrations are not reliable
indicators of calcium homeostasis, and that measurement of
HYPERCALCEMIA serum ionized calcium concentration is preferred, especially
in animals with hypoproteinemia.
Identification The biologically active, ionized fraction of calcium can be
Hypercalcemia is present if the serum calcium concentra- determined directly; this approach bypasses the influence of
tion is greater than 12 mg/dL (dog) and 11 mg/dL (cat) or plasma proteins on the total serum calcium concentration.
if the serum ionized calcium concentration is greater than Ionized calcium measurements are superior to serum total
1.5 mmol/L (dog) and 1.3 mmol/L (cat), although refer- calcium measurements for assessing calcium in dogs and
ence ranges may vary between laboratories. The serum total cats. Automated equipment that uses a calcium ion-selective
and ionized calcium concentrations are higher in puppies electrode allows accurate measurement of ionized calcium
than in adult dogs. A mild increase in serum total calcium in blood, plasma, or serum. Ionized calcium results can be
(i.e., <13 mg/dL), ionized calcium (i.e., <1.55 mmol/L), and affected by many variables, including method of sample
phosphorus (i.e., <10 mg/dL) concentrations in a clinically collection (samples collected anaerobically provide more
healthy puppy, together with an increase in serum alka- precise results); amount and type of heparin, if used (may
line phosphatase activity and normal urea nitrogen and underestimate or overestimate ionized calcium results);