Today's Veterinary Practice

SEP-OCT 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEWED 44 SEPTEMBER/OCTOBER 2018 REVIEWED PEER Electrolyte disturbances are frequently encountered in veterinary patients and may warrant close evaluation and monitoring. Diseases of the kidneys and gastrointestinal tract and endocrinopathies often result in changes to electrolytes. 1-3 Accurate initial assessment and serial monitoring for trends in electrolyte disturbances are essential to guide appropriate treatment of the underlying condition. However, in certain situations, biochemical analysis and electrolyte results may be misleading and overstate or even fail to identify crucial electrolyte disturbances. This article discusses situations in which normal laboratory results may lead to failure to diagnose, and thus treat, common electrolyte disturbances in clinical practice. SODIUM Sodium is the principal extracellular cation in dogs and cats and is primarily responsible for maintaining serum osmolality. 4 It is generally maintained within a relatively narrow range in dogs and cats, despite large variations in both sodium and water intake. 2-4 The kidney regulates sodium balance through various mechanisms, including the renin-angiotensin-aldosterone system, neurohormonal mechanisms, and atrial and brain natriuretic peptides. 2-4 Serum osmolality is determined by the concentrations of sodium, urea, and glucose. However, only sodium and glucose are considered effective osmoles, meaning they do not freely cross cell membranes. 2,3 "Pseudohyponatremia" describes hyponatremia in a patient with a normal or increased serum osmolality. This can occur in patients with hyperlipidemia, hyperproteinemia, or hyperglycemia or after mannitol infusion. 2,3 The most common cause of pseudohyponatremia in veterinary patients is hyperglycemia secondary to diabetes mellitus. 2 Because glucose is an effective osmole, hyperglycemia can precipitate an increase in extracellular fluid water, causing a dilutional decrease in serum sodium concentrations. 2,3 In people with hyperglycemia, each 100-mg/dL increase in glucose decreased serum sodium concentrations by 1.6 mEq/L up to blood glucose concentrations of 440 mg/dL, but correction was even greater at higher blood glucose concentrations. 5 Thus, a normal serum sodium concentration in a severely hyperglycemic patient should be closely evaluated and a corrected serum sodium concentration should be calculated as follows: 2 Na + (corr) = Na + (meas) + 1.6([measured glucose – normal glucose]/100) For example, a diabetic patient with a blood glucose concentration of 1000 mg/dL and a "normal" measured Are Normal Electrolytes Really Normal? Leonel Londoño, DVM, DACVECC, Jennifer Martinez, DVM University of Florida College of Veterinary Medicine, Gainesville, Florida CRITICAL CARE Guidi

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