Page 184 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

174 ELECTROLYTE DISORDERS

a veterinary clinic. This could explain the phenomenon of possible because the amino-terminal portions of PTH
mild stress-induced seizures or tetany in dogs that have are highly conserved, function in vivo in animals, and
hypocalcemia, as the alkalosis shifts some calcium to the would be unlikely to elicit an immune response.
protein-bound state, causing more severe ionized Hypocalcemia severe enough to cause clinical signs
hypocalcemia. should be anticipated in dogs undergoing parathyroidec-
tomy as treatment for hypercalcemia related to a parathy-
TREATMENT OF HYPOCALCEMIA roid gland adenoma. Animals with very high
Puerperal tetany is the condition most likely to require concentrations of serum calcium, PTH, and serum ALP
correction of hypocalcemia acutely, but chronic treat- maybeatgreaterriskofdevelopingpostoperativehypocal-
ment is not needed. Hypoparathyroidism is the only con- cemia. Postoperative hypocalcemia in this instance is the
dition requiring acute and chronic treatment to alleviate consequence of acute hypoparathyroidism resulting from
clinical signs of hypocalcemia. Other conditions chronic suppression of remaining parathyroid glands and
associated with hypocalcemia are transient or result in calcium uptake into “hungry” bones. Hypocalcemia
minimal decreases in serum calcium concentration, do should be anticipated in cats that undergo bilateral thy-
not cause obvious clinical signs, and only occasionally roidectomy, because up to 30% of cats can be expected
necessitate calcium replacement therapy. No treatment to have transiently lowered serum calcium concentrations.
is indicated for hypocalcemia attributable entirely to Therapy should be instituted before the development
hypoalbuminemia or hypoproteinemia, assuming that of tetany. Preemptive therapy to increase serum calcium
the iCa fraction is normal. concentration may be a good choice for animals with
Treatment is individualized based on severity of clinical marked hypocalcemia with no apparent clinical signs or
signs, magnitude of hypocalcemia, rapidity of decline in for those in which serum calcium concentration is steadily
serum calcium concentration, and trend of serial serum or rapidly declining. Prophylactic therapy to prevent
calcium measurements (i.e., further decrease or stability). hypocalcemia in dogs undergoing surgery for hyperpara-
Aggressive treatment is prescribed for patients with severe thyroidism should be considered, especially in dogs with
clinical signs of hypocalcemia, patients with severe ion- severe hypercalcemia. Active vitamin D metabolites
ized hypocalcemia with or without signs, and patients should be started before surgery in these instances
in which serum calcium concentration is steadily or rap- because there is a lag time until maximal effect is achieved.
idly declining. Acute, subacute, and chronic rescue treat- Vitamin D metabolites given at the time of surgery or
ment regimens are available using supplementation with just after surgery fail to prevent development of
calcium salts and vitamin D metabolites. The goal of ther- hypocalcemia.
apy is to increase serum calcium concentration to a level Autotransplantation of normal parathyroid glands is a
that alleviates the signs of hypocalcemia, minimizes the treatment option used to minimize postoperative hypo-
likelihood of the development of hypercalcemia, and calcemia when it is obvious that damage has been done
reduces the magnitude of hypercalciuria (especially in to the parathyroid glands during surgery (bilateral
patients with hypoparathyroidism). It is usually not nec- extracapsular thyroidectomy). Autotransplantation of
essary or desirable to return serum calcium concentration normal parathyroid glands was studied in experimental
completely to normal because many clinical signs improve cats following bilateral extracapsular thyroparathy-
dramatically with slight increases in serum calcium con- roidectomy. 425 External parathyroid glands were
centration, and the consequences of overcorrection can harvested and dissected from thyroid tissue, and small
be serious. For suspected temporary postsurgical hypo- pieces of parathyroid tissue were embedded into the
parathyroidism, it is desirable to keep the serum calcium sternohyoideus muscle. Cats showed an average decrease
concentration relatively low to maximize compensatory of 44% in serum tCa with the nadir occurring 1.9 days fol-
hypertrophy of remaining parathyroid glands. lowing surgery. Hypocalcemia was present for a median
In patients with hypoparathyroidism, no treatment of 14 days in cats having parathyroidectomy and
regimen completely compensates for the full range of autotransplantation in this study compared with a median
physiologic actions of the absent PTH. Vitamin D metab- of 71 days in cats of a previous report involving parathy-
olite treatment corrects the low intestinal absorption of roidectomy without autotransplantation. 188 Seven of
calcium but does not completely protect the kidneys from eight cats with autotransplantation of parathyroid glands
hypercalciuria as would occur in the presence of PTH. regained normocalcemia within 20 days without oral
Similarly, vitamin D metabolites do not exert as powerful calcium salt supplementation. 425
an effect on bone in the absence of PTH. Replacement
therapy with once-daily subcutaneous injections of Acute Management of Hypocalcemia
human PTH (1-34) in human subjects was highly effec- Causing Tetany or Seizures
tive in providing good 24-hour control of serum calcium Tetany or seizures caused by hypocalcemia require treat-
concentration. 616 Use of synthetic human amino-termi- ment with intravenously administered calcium salts. Cal-
nal PTH for the treatment of veterinary patients is cium is administered to effect, at a dosage of 5 to 15 mg/