Page 178 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

168 ELECTROLYTE DISORDERS

rarely occur before whelping. 103 In 31 dogs with muscles. Symptomatic hypocalcemia resulting in death
periparturient hypocalcemia, iCa was less than the refer- of three dystrophin-deficient cats occurred following
ence range, and small breed dogs with large litters were anesthesia or mild exertion during restraint and
typical. 152 Median time from whelping to detection of subsequent acute rhabdomyolysis. 208 Hypocalcemia was
clinical signs was 14 days, but variation was wide. Clinical documented along with hyperphosphatemia, increased
signs most often included seizures, trembling, twitching, liver transaminases, and massive increases in creatine
shaking, and stiffness. Nontypical signs included panting, kinase. Hypocalcemia has been described in some dogs
behavioral changes, collapse, and whining; vomiting, diar- with fatal Vipera xanthina palestinae envenomation. 17
rhea, and choking were rare. Rectal temperature was ele- The origin of the hypocalcemia may be multifactorial,
vated, attributable to increased muscle activity. After including muscle necrosis. Renal transplantation in14cats
treatment with intravenous calcium gluconate (mean resulted in decreased iCa in the 5-day postoperative
dose, 115 mg/kg), iCa concentration normalized within period. 624 All cats also had decreased serum iMg but
25 minutes in 90% of dogs. Most dogs received more than normal tMg.
one injection of calcium gluconate, but the total calcium
dose given did not correlate to initial iCa concentration.
In one lactating bitch, severe hypocalcemia and hypomag- Small Intestinal Diseases
nesemia occurred in association with acute onset of gastric Hypocalcemia may occur in association with gastrointesti-
and bladder atony, congestive heart failure, weakness, and nal disease. Ionized calcium concentration was below the
paresis without muscle fasciculation or seizures. 16 reference range (mean, 0.99 0.19 mmol/L; reference
Puerperal tetany is rare in cats. 602 Eclampsia was range, 1.13 to 1.33 mmol/L) in 12 dogs with intestinal
317
described in four cats in which hypocalcemia developed lymphangiectasia. Tenof13dogshadhypoalbuminemia
3 to 17 days before parturition. 174 Signs of depression, with a mean of 2.12 0.70 g/dL, and “corrected”
weakness, tachypnea, and mild muscle tremors were most serum tCa was discordant with iCa measurement.
common; vomiting and anorexia were less common, and Mechanisms for hypocalcemia could include calcium/fatty
prolapse of the third eyelid occurred in some cats. Hypo- acid complexes in the intestinal lumen that could
thermia, instead of hyperthermia as seen in dogs, was decrease intestinal calcium absorption. Hypovitaminosis
observed. All cats responded to parenteral calcium gluco- D from malabsorption or hypomagnesemia may have
nate initially and to oral calcium supplementation contributed to hypocalcemia but was not evaluated.
throughout gestation and lactation. No dogs had clinical signs associated with hypocalcemia.
Ionized hypocalcemia is common in cats with urethral In five Yorkshire terriers and a shih tzu with protein-
obstruction and is likely to develop in cats that also have losing enteropathy, iCa and tMg concentrations were
hyperkalemia and metabolic acidosis. Cats with severe moderately to severely low. 92,294 Concentration of PTH
ionized hypocalcemia can exhibit compromised vital was increased (secondary hyperparathyroidism), and 25-
functions, although most survive with relief of urethral hydroxyvitamin D concentration was below the reference
obstruction. In 199 cats with urethral obstruction, iCa range. It is not clear whether the apparent elevation in
was below the reference range in 34%, normal in 47%, PTH was increased to an appropriate level in the face of
and above the reference range in 19%. 324 Of those with low iCa, or whether maximum production was suppressed
low iCa, 14% had moderate and 6% had severe hypocalce- because of the effects of hypomagnesemia. Intravenous
mia. In an earlier study, 75% of cats with urethral obstruc- supplementation with fluids containing magnesium salts
tion exhibited low iCa. 153 Most of these cats had elevated resulted in increases in PTH and iCa; 25-hydroxyvitamin
tMg, probably from reduced renal function at the time of D remained below the reference range. 92 Following
obstruction. Hypomagnesemia is not likely to account for 8 weeks of treatment for inflammatory bowel disease, cal-
the development of hypocalcemia in these cats, but iMg cium homeostasis was normal based on normal iCa, PTH,
was not measured. Calcium regulatory hormones were tMg, and 25-hydroxyvitamin D concentrations. Magne-
not evaluated in either of these studies. Alkalinizing sium repletion apparently resulted in resolution of hypo-
infusions designed to correct metabolic acidosis or for calcemia largely because of increased PTH secretion,
translocation of potassium into cells are often considered whereas 25-hydroxyvitamin D concentration was still
for treatment of cats with urethral obstruction, but these low. Resolution of weakness may have been the result of
can decrease tCa and iCa concentrations. 114 correction of hypocalcemia, hypomagnesemia, or both.
Rhabdomyolysis is sometimes associated with hypocal- Low iCa concentration with elevated PTH and low
cemia, but clinical signs of hypocalcemia are rare. Mild concentrations of both 25-hydroxyvitamin D and
hypocalcemia in dogs and cats with severe vehicular mus- calcitriol were also noted in two dogs with protein-losing
cle trauma is occasionally observed (Chew, personal enteropathy. 371 One dog was diagnosed with
observations). Hypocalcemia likely occurs as a conse- lymphangiectasia, and the other was diagnosed with
quence of translocation of calcium into the damaged chronic lymphocytic/plasmacytic enteritis.