Hypocalcemia

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Hypocalcemia is defined as a blood ionized calcium (iCa) level < 6.5 mg/dL (< 1.25 mmol/L) (normal 9 - 11.4 mg/dL).

Serum total calcium does not accurately predict ionized calcium status in many clinical conditions[1]. Calcium homeostasis in hypoalbuminemic critically ill dogs should be evaluated by iCa concentrations rather than total calcium or calcium adjusted for albumin or total protein[2].

Calcium is a vital intracellular and extracellular ion involved in neuronal activation, muscle contraction, enzymatic reactions, hormone secretion, and bone matrix.

Normal calcium homeostatic mechanisms maintain extracellular calcium concentrations within a narrow normal range and changes often result in abnormal skeletal and cardiac muscle activity.

Extracellular calcium exists in three forms: ionized (the biologically active form), complexed (to plasma buffers), and protein-bound (mainly to albumin). Most commonly, total calcium is measured on serum biochemical analyses and represents the sum of all calcium fractions. Serum-ionized calcium (iCa) concentration is a more accurate measure of hypercalcemia than total serum calcium or corrected serum calcium concentrations[3].

In dogs with hypocalcemia, the low concentration of calcium causes an excitatory effect on nerve and muscle cells, lowering the threshold potential and discharging repetitively without provocation. Tetany occurs as a result of spontaneous repetitive firing of motor nerve fibers.

Hypoglycemia can occur concurrently in dogs.

Although commonly observed in young dogs associated with inadequate dietary calcium, a number of disease may also cause hypocalcemia, including:

Dogs with hypocalcemia may be clinically normal, but sever hypocalcemia may cause shivering, muscle fasciculation and seizures[15].

In dogs with nutritional secondary hyperparathyroidism, clinically affected dogs often present with joint pain due to osteopenia, which can be confirmed on radiographs[16].

Treatment involves addressing the acute hypocalcemia with parenteral calcium gluconate (10 mL of 10% calcium gluconate in 250 mL of 0.9% saline administered at 2.5 mL/kg/hr for 8 – 12 hours).

Severe and persistent hypocalcemia is associated with ventricular tachyarrhythmias and fibrillation, leading to sudden death[17].

References

  1. Schenck PA & Chew DJ (2008) Calcium: total or ionized? Vet Clin North Am Small Anim Pract 38(3):497-502
  2. Sharp CR et al (2009) A comparison of total calcium, corrected calcium, and ionized calcium concentrations as indicators of calcium homeostasis among hypoalbuminemic dogs requiring intensive care. J Vet Emerg Crit Care (San Antonio) 19(6):571-578
  3. Messinger JS et al (2009) Ionized hypercalcemia in dogs: a retrospective study of 109 cases (1998-2003). J Vet Intern Med 23(3):514-519
  4. LeVine DN et al (2009) Hereditary 1,25-dihydroxyvitamin D-resistant rickets in a Pomeranian dog caused by a novel mutation in the vitamin D receptor gene. J Vet Intern Med 23(6):1278-1283
  5. Hume DZ et al (2006) Outcome of dogs with diabetic ketoacidosis: 127 dogs (1993-2003). J Vet Intern Med 20(3):547-555
  6. Krook L & Whalen JP (2011) Nutritional secondary hyperparathyroidism in the animal kingdom: report of two cases. Clin Imaging 34(6):458-461
  7. Drobatz KJ & Casey KK (2000) Eclampsia in dogs: 31 cases (1995-1998). J Am Vet Med Assoc 217(2):216-219
  8. Kimmel SE et al (2000) Hypomagnesemia and hypocalcemia associated with protein-losing enteropathy in Yorkshire terriers: five cases (1992-1998). J Am Vet Med Assoc 217(5):703-706
  9. Arbaugh M et al (2012) Evaluation of preoperative serum concentrations of ionized calcium and parathyroid hormone as predictors of hypocalcemia following parathyroidectomy in dogs with primary hyperparathyroidism: 17 cases (2001-2009). J Am Vet Med Assoc 241(2):233-236
  10. Holowaychuk MK & Monteith G (2011) Ionized hypocalcemia as a prognostic indicator in dogs following trauma. J Vet Emerg Crit Care (San Antonio) 21(5):521-530
  11. Tomsa K et al (2001) Life threatening metabolic disorders after application of a sodium phosphate containing enema in the dog and cat. Schweiz Arch Tierheilkd 143(5):257-261
  12. Kook PH et al (2009) Pancreatitis associated with clomipramine administration in a dog. J Small Anim Pract 50(2):95-98
  13. Gow AG et al (2011) Hypovitaminosis D in dogs with inflammatory bowel disease and hypoalbuminaemia. J Small Anim Pract 52(8):411-418
  14. Luschini MA et al (2010) Incidence of ionized hypocalcemia in septic dogs and its association with morbidity and mortality: 58 cases (2006-2007). J Vet Emerg Crit Care (San Antonio) 20(4):406-412
  15. Brauer C et al (2011) Metabolic and toxic causes of canine seizure disorders: A retrospective study of 96 cases. Vet J 187(2):272-275
  16. Hutchinson D et al (2012) Seizures and severe nutrient deficiencies in a puppy fed a homemade diet. J Am Vet Med Assoc 241(4):477-483
  17. Ricco ML et al (2009) Effects of hypocalcemia on electrical restitution and ventricular fibrillation. Conf Proc IEEE Eng Med Biol Soc 2009:4182-4185
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