Page 177 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Disorders of Calcium: Hypercalcemia and Hypocalcemia 167

azotemia. 27 In 73 cats with CRF, none had hypocalcemia not any specific diagnosis. 644 The impact of hypocalcemia
based on tCa, but 3% of cats with moderate CRF and 23% on patient survival has not yet been determined, although
of cats with advanced CRF did have hypocalcemia. In 47 in one study, hypocalcemia and higher levels of PTH were
cats with CRF, 14% with moderate CRF and 56% with more frequently associated with fatality. 106
advanced CRF had ionized hypocalcemia. Mean iCa for Ionized calcium concentration decreased in experi-
cats with advanced CRF was significantly lower than mental dogs with hemorrhage-caused hypotension and
values from normal cats or cats with mild and moderate continued to decline during replacement of blood vol-
CRF. Hypocalcemia was underappreciated when based ume with citrated whole blood. 56 Hemorrhage also
on results of tCa measurement, especially with advancing decreases iCa concentration in clinical dogs. Massive
azotemia. transfusions in 10 dogs resulted in significant ionized
AIRF and postrenal failure can result in hypocalcemia hypocalcemia. 282
that is more likely to be symptomatic because the degree Cardiopulmonary resuscitation (CPR) may result in
of hyperphosphatemia is often greater than that observed hypocalcemia. Dogs developed ionized hypocalcemia
in CRF. Dogs with AIRF had a mean serum tCa concen- within 5 minutes of starting CPR in dogs with prolonged
tration of 9.8 1.7 mg/dL, but iCa was not reported. 589 cardiac arrest and continued to decrease after 20
Secondary hyperparathyroidism is common in associa- minutes. 93,415 Serum tCa was not concordant with
tion with renal failure, and is characterized by low or changes in iCa because mean serum tCa did not change,
normal ionized calcium with elevated circulating concen- and iCa concentrations were negatively associated with
tration of serum PTH. In a study of 54 dogs with chronic lactate concentrations. Decreased iCa was most likely
kidney disease, secondary hyperparathyroidism was pres- related to formation of complexes with lactate.
130
ent in 76% of all dogs. In nonazotemic kidney disease In horses with enterocolitis, decreased iCa was
(IRIS stage 1), 36% of dogs already had developed sec- identified in nearly 80% of patients. 575 Ionized hypocalce-
ondary hyperparathyroidism. With mild azotemia (IRIS mia was associated with decreased iMg, increased serum
stage 2), 50% ofdogs had developedsecondary hyperpara- phosphorus, decreased fractional urinary excretion of cal-
thyroidism, and with moderate azotemia (IRIS state 3), cium, and increased PTH in 71% of cases. Hypocalcemia
96% had secondary hyperparathyroidism. By the time in 29% of these horses was a result of inadequate secretion
severe azotemia was present (IRIS state 4), 100% of dogs of PTH, although impaired mobilization of calcium from
had developed secondary hyperparathyroidism. bone and loss or sequestration of calcium within the gas-
trointestinal tract could not be excluded.
Emergency and Critical Care Acute pancreatitis may be associated with hypocalcemia.
Ionized hypocalcemia is common in critically ill humans in In46catswithacutepancreatitis,iCaconcentrationwaslow
the intensive care setting and is more common in septic in 61% of cats. 295 Suggested mechanisms that may account
patients. 106,333,644 The magnitude of hypocalcemia is forlowiCainacutepancreatitisincludesequestrationofcal-
correlated to severity of illness. Hypocalcemia with critical cium into peripancreatic fat (saponification), increased free
illness also occurs in veterinary patients. 145,257 The causes fatty acids, increased calcitonin secondary to hyperglu-
of hypocalcemia in critical illness appear to be multifacto- cagonemia, and PTH resistance or deficit resulting from
rial because sepsis, systemic inflammatory response syn- the effects of hypomagnesemia. 45,145,277,505
drome, hypomagnesemia, blood transfusions, and AIRF In dogs with diabetes mellitus, 47% had ionized hypo-
have been associated with hypocalcemia. 145,332,636,644 In calcemia. 244 Normal iCa concentrations were noted in
humans, hypocalcemia associated with critical illness 49.4% of dogs from this study, and 3.5% had ionized
involves decreased PTH secretion, hypercalcitonism, hypercalcemia. Acute pancreatitis was diagnosed in 13%
and altered calcium binding to proteins. 465 The cause of of these dogs, which could be the mechanism in some
the hypocalcemia is not related to enhanced urinary cal- but not all of those with hypocalcemia. In a study of
cium excretion, decreased bone mobilization, or blunted 127 dogs with diabetic ketoacidosis, 52% exhibited ion-
secretion of PTH in septic patients. 333 The presence of ized hypocalcemia. 286 Dogs that did not survive had
proinflammatory cytokines during sepsis is related to the lower iCa concentrations than those that did survive.
development of hypocalcemia in septic patients. 333 PTH Puerperal tetany (eclampsia) typically occurs between
is commonly elevated in this population even when 1 and 3 weeks postpartum in females of small dog breeds
normocalcemia exists. 106,333 In a study of 141dogs admit- and is attributed to loss of calcium into milk during lac-
ted to an intensive care unit, 16% showed hypocalcemia tation, although parathyroid gland dysfunction has not
based on iCa concentration. 257 Hypocalcemia was been conclusively excluded. 21,179 Proposed mechanisms
associated with longer intensive care unit and hospital for hypocalcemia include a poor dietary source of cal-
stays, but was not associated with decreased survival. Dogs cium, major loss of calcium during lactation, fetal skeletal
with sepsis were more likely to exhibit hypocalcemia. ossification, and abnormal parathyroid gland function,
Up to 88% of hospitalized human patients had including parathyroid gland atrophy. Hypophosphatemia
decreased iCa that correlated to severity of illness but may accompany the hypocalcemia, and clinical signs