What Are Electrolytes?

Electrolytes are electrically charged salts and metal compounds measured in the serum. Five of the most significant and clinically important electrolytes in dogs and cats include sodium, potassium, chloride, magnesium, and calcium. Calcium, sodium, and chloride are the major electrolytes in extracellular fluid; potassium and magnesium are major electrolytes in intracellular fluid alongside proteins.¹ These compounds keep the intracellular and extracellular compartments in osmotic equilibrium, and those solutes that are osmotically active (sodium, chloride, and potassium) determine water distribution and balance.² Along with muscle and nerve functions, they maintain membrane potentials and act as cofactors in enzyme-mediated reactions.²

The Impact of Electrolyte Imbalance

Too often, we casually glance over electrolyte imbalances on a patient's biochemistry profile. Yet, these blood abnormalities are often one of the first signs veterinarians may have, leading to a diagnosis of cardiovascular, kidney, and gastrointestinal disease and many endocrinopathies. Let's dive deeper into electrolytes and what clinical signs a patient may demonstrate with an electrolyte disturbance.

Sodium

Sodium is the predominant extracellular cation in our patients, and its primary role is maintaining serum osmolality.³ The kidney is primarily responsible for sodium balance through several hormones, the renin-angiotensin-aldosterone system, and atrial and brain natriuretic peptides.^3-5 When we see imbalance, patients can be hypo- or hypernatremia; however, both present neurologically, with disorientation, head pressing, ataxia, behavior changes, seizures, or coma.⁶

Potassium

Potassium is the predominant intracellular cation, and it maintains resting membrane potentials or the degree of cellular excitability.⁷ Similar to sodium, we can see clinical disease with both hypokalemia and hyperkalemia. Hypokalemic and hyperkalemic patients can both present with neuromuscular weakness and cardiac conduction abnormalities. However, hypokalemic patients will demonstrate ventricular tachycardia and ventricular fibrillation, whereas hyperkalemic patients will present with bradycardia and, in severe cases, atrial standstill.^8-9

Magnesium

Magnesium is also an intracellular cation that has gained more recent attention in veterinary medicine. It has many roles in the body, including protein synthesis, activation of T cells, acting as a co-enzyme for the sodium-potassium adenosine triphosphatase pump, and depolarization of myocardial cells and neurons.^10-12 This electrolyte imbalance acts most commonly like a deficiency, and this should be suspected in patients with mental depression, hemolysis, anorexia, nausea, ileus, muscle weakness, cardiac arrhythmias, and even refractory hypokalemia and hypocalcemia.^10-11

Chloride

Chloride is about two-thirds of the extracellular fluid anions and significantly influences acid-base balance. There are technically no clinical signs of hypo- or hyperchloremia, but this imbalance can result in acid-base disruption and complications discussed later. Recent research suggests hypochloremia could serve as a marker of disease severity and therapeutic response in dogs with acute congestive heart failure.¹³

Calcium

Calcium is a mineral that has many functions in the body besides structural integrity of bones and teeth. It assists in nerve conduction and muscle contraction, assists proteins in the clotting cascade, and binds with other chemicals within the body. Our patients receive calcium from intestinal absorption in conjunction with vitamin D and from bone resorption when levels are low. This syndrome, hypocalcemia, is frequently seen in our patients with pancreatitis, kidney failure, parathyroid gland failure, and antifreeze poisoning. These patients show muscle twitching, anorexia, weakness, seizures, and can be fatal.¹⁴ Alternatively, hypercalcemia can be due to hypoadrenocorticism, a parathyroid gland tumor, neoplasia, anal gland adenocarcinoma, and also kidney failure. These patients can look very similar to the hypocalcemic pet except excessive calcium can also cause polyuria, polydipsia, as well as uroliths or nephroliths.

How Electrolyte Testing Can Lead to a Diagnosis

Many veterinarians tend to pay more attention to the major organ function tests or enzyme changes in blood work results. However, the electrolyte imbalances found in lab work can be one of the subtle but critical clues leading to a more specific diagnosis of kidney disease, heart disease, or gastrointestinal disorders. Remember that it may not be the absolute value of imbalance, but the pattern of electrolyte changes pointing to disease. A perfect example of this is the change in sodium to potassium ratio, which can strongly suggest canine hypoadrenocorticism.

There are other examples of this. For instance, diarrhea due to disease in the gastrointestinal tract can cause decreased sodium and bicarbonate serum levels. Diseased kidneys cannot eliminate excessive phosphorus and potassium in the urine; one or both of these electrolytes may be elevated in lab work. Elevated potassium may indicate urinary obstruction or cardiovascular disease, often seen as cardiac arrhythmias.

Electrolyte Testing as a Monitoring Tool

Electrolyte levels on lab work are not just important for diagnosis but are equally helpful when used as a monitoring tool. Whether a patient is being managed for chronic kidney disease, hypoadrenocorticism, chronic inflammatory diseases of the gastrointestinal tract, or some of the other endocrine disorders involving the parathyroid gland, resolution of electrolytes not only can indicate successful treatment but can also help improve the patient's quality of life.

Timely Electrolyte Testing Is Essential

While some electrolyte disorders are mild, many of the electrolyte imbalances discussed result in significant clinical signs that can indicate severe to life-threatening diseases such as an Addisonian crisis, diabetic ketoacidosis, autoimmune hemolytic anemia, or cardiac arrhythmia from urinary obstruction. A 2017 study even suggested that disturbances in sodium, potassium, corrected chloride, or ionized calcium concentrations above or below the midpoint of the reference interval are associated with death in dogs evaluated in an emergency room or intensive care unit.¹⁵ The earlier veterinarians can intervene, assess electrolyte levels, and request additional diagnostic testing, the quicker a diagnosis can be reached and interventional therapy can begin.

References

1. Madhavan Unny, N., Zarina, A., Beena, V. (2023). Fluid and Electrolyte Balance. In: Das, P.K., Sejian, V., Mukherjee, J., Banerjee, D. (eds) Textbook of Veterinary Physiology. Springer, Singapore.
2. Chapter 14 - Clinical Pathology, A Comprehensive Guide to Toxicology in Nonclinical Drug Development (Second Edition), Academic Press, 2017, Chapter 14, Pages 325-374.
3. Sakr Y, Rother S, Ferreira AM, et al. Fluctuations in serum sodium level are associated with an increased risk of death in surgical ICU patients. Crit Care Med 2013;41:133-142.
4. Burkitt Creedon JM. Sodium disorders. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine, 2nd ed. St. Louis: Elsevier; 2015:263-268.
5. Dibartola SP. Disorders of sodium and water: hypernatremia and hyponatremia. In: Dibartola SP, ed. Fluid, Electrolyte and Acid-Base Disorders in Small Animal Practice, 4th ed. St. Louis: Elsevier; 2012:45-79.
6. Burkitt Creedon JM. Sodium disorders. Electrolyte and acid base disturbances, 2nd ed. In: Silverstein DC, Hopper K (eds). : Saunders Elsevier; 2015
7. Riordan LL, Schaer M. Potassium disorders. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine, 2nd ed. St. Louis: Elsevier; 2015:269-273.
8. Dibartola SP, De Morais HA. Disorders of potassium: hypokalemia and hyperkalemia. In: Dibartola SP, ed. Fluid, Electrolyte and Acid-Base Disorders in Small Animal Practice, 4th ed. St. Louis: Elsevier; 2012:92-119.
9. Tag TL, Day TK. Electrocardiographic assessment of hyperkalemia in dogs and cats. J Vet Emerg Crit Care 2008;18:61-67.
10. Humphrey S, Kirby R, Rudloff E. Magnesium physiology and clinical therapy in veterinary critical care. J Vet Emerg Crit Care (San Antonio) 2015;25:210-225.
11. Martin LG, Allen-Durrance AE. Magnesium and phosphate disorders. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine, 2nd ed. St. Louis: Elsevier; 2015:281-288.
12. al-Ghamdi SM, Cameron EC, Sutton RA. Magnesium deficiency: pathophysiologic and clinical overview. Am J Kidney Dis 1994;24:737-752.
13. Roche-Catholy M, Van Cappellen I, Locquet L, Broeckx BJG, Paepe D, Smets P. Clinical relevance of serum electrolytes in dogs and cats with acute heart failure: A retrospective study. J Vet Intern Med. 2021 Jul;35(4):1652-1662.
14. Dias C, Carreira LM. Serum ionised calcium as a prognostic risk factor in the clinical course of pancreatitis in cats. J Feline Med Surg (2015) 17:984–90.
15. Goggs R, De Rosa S, Fletcher D. Electrolyte disturbances are associated with non-survival in dogs – a multivariable analysis. Frontiers in Veterinary Science (2017), 4: 135.