Definition

Serum potassium concentration <3.5 mEq/L (normal range: 3.5–5.5 mEq/L).

Pathophysiology

• Potassium is primarily an intracellular electrolyte (98% of total body potassium is intracellular); serum levels, however, may not accurately reflect total body concentrations.
• It is predominantly responsible for the maintenance of intracellular fluid volume and required for normal function of many enzymes.
• The resting cellular membrane potential is determined by the ratio of intracellular to extracellular potassium concentration and maintained by the Na⁺, K⁺-ATPase pump. Conduction disturbances in susceptible tissues (cardiac, nerve, and muscle) are caused by rapid shifts in this ratio causing myoneural membrane hyperpolarization.
• Hypokalemia can be caused by decreased intake, loss (via the gastrointestinal tract or kidneys), or translocation of potassium from the extracellular to the intracellular fluid space.

Systems Affected

• Neuromuscular-muscle weakness, including skeletal and muscles of respiration.
• Cardiac-electrocardiac changes and arrhythmias.
• Renal-hyposthenuria, nephropathy, and renal failure.
• Metabolic-acid-base balance (metabolic alkalosis); glucose homeostasis.

Signalment

• Dogs and cats with predispositions to increased potassium loss, translocation of potassium, or decreased intake of potassium.
• Young Burmese cats with recurrent hypokalemic periodic paralysis episodes.

Signs

• Generalized muscle weakness or paralysis
• Muscle cramps
• Lethargy and confusion
• Vomiting
• Anorexia
• Carbohydrate intolerance and weight loss
• Polyuria
• Polydipsia
• Decreased bowel motility (humans; maybe dogs and cats)
• Hyposthenuria
• Ventroflexion of the neck (cats and dogs)
• Respiratory muscle failure

Causes

Risk Factors

• Acidifying diets with negligible potassium
• Diuresis or dialysis with potassium-deficient fluids
• Chronic illness (sustained anorexia and muscle wasting)

Differential Diagnosis

• PU/PD, hyperglycemia, and glucosuria-rule out diabetes mellitus.
• PU/PD, azotemia, and isosthenuria-rule out chronic renal failure and nephropathy.
• Vomiting, metabolic alkalosis, and hypochloremia-rule out upper gastrointestinal obstruction.
• Metabolic acidosis with urine pH >6.5-rule out renal tubular acidosis.
• Urethral obstruction-rule out post-obstructive diuresis.
• Young Burmese cat with episodic muscle weakness-rule out hypokalemic periodic paralysis.

Laboratory Findings

CBC/Biochemistry/Urinalysis

• Hyperglycemia, glucosuria, ± ketonuria, ± ketoacidosis in patients with diabetes mellitus.
• Normocytic, normochromic, nonregenerative anemia in patients with chronic renal failure.
• Elevated BUN and creatinine, with isosthenuria in patients with chronic renal failure or hypokalemic nephropathy.
• Low total CO₂ or HCO₃^– in patients with renal tubular acidosis (RTA) or renal failure.
• Normal anion gap metabolic acidosis in RTA.
• Urine pH >6.5 in patients with distal tubular acidosis.
• High total CO₂ or HCO₃^– in patients with metabolic alkalosis.

Other Laboratory Tests

• Increased aldosterone and decreased renin in patients with primary hyperaldosteronism.
• Elevated urinary fractional excretion of potassium in patients with chronic renal failure or hypokalemic nephropathy.
• ACTH stimulation tests are used to diagnose adrenal gland disorders.

Imaging

• Radiography, ultrasonography are helpful to diagnose gastrointestinal tract obstructions (mass or foreign bodies), pancreatitis, chronic renal failure workup, adrenal gland diseases (hyperadrenocorticism, hyperaldosteronism, and adrenal tumors).
• Upper gastrointestinal barium study to additionally diagnose gastrointestinal obstructions (anatomic or functional).
• Computed tomography or magnetic resonance imaging to further diagnose adrenal gland diseases.

Other Diagnostic Procedures

Upper gastrointestinal endoscopy to diagnose upper gastrointestinal disorders.

Drug(s) Of Choice

• Oral supplementation with potassium gluconate (e.g., Tumil-K) is effective in mildly affected patients. The initial dosage is 1/4 teaspoon (2 mEq) per 4.5 kg body weight in food twice daily.

• Parenteral supplementation is required in anorectic or vomiting patients or in patients with moderate-to-severe hypokalemia (<3.0). Potassium chloride is added to intravenous fluids according to Table 1, best delivered via infusion pump or with a pediatric fluid administration set (60 drops/mL/minute). Monitor and taper accordingly.

Contraindications

• Glucose supplementation
• Insulin administration
• Sodium bicarbonate administration
• Untreated hypoadrenocorticism
• Hyperkalemia
• Renal failure or severe renal impairment
• Acute dehydration
• Severe hemolytic reactions
• Impaired gastrointestinal motility

Precautions

Administer with caution, avoid oversupplementation, monitor frequently.

Possible Interactions

Concurrent potassium supplementation with ACE inhibitors (e.g., enalapril), potassium-sparing diuretics (e.g., spironolactone), prostaglandin inhibitors (e.g., nonsteroidal anti-inflammatory drugs), beta-blockers (e.g., atenolol), or cardiac glycosides (e.g., digoxin) can cause adverse effects.

Alternative Drug(s)

Potassium phosphate can be used in patients with concurrent hypophosphatemia where one-half of the potassium dose is administered in the form of potassium phosphate solution.

Patient Monitoring

Check serum potassium every 6–24 hours based on severity of hypokalemia.

Possible Complications

Electrolyte disturbances and arrhythmias. It is essential to close the IV fluid outflow valve and thoroughly mix the fluid contents while adding potassium chloride solution to the parenteral fluid bag.

Associated Conditions

• Hypokalemic nephropathy
• Hypophosphatemia
• Hypomagnesemia
• Metabolic alkalosis

Age-Related Factors

None

Zoonotic Potential

None

Pregnancy/Fertility/Breeding

N/A

See Also

• Alkalosis, Metabolic
• Diarrhea chapters
• Hypochloremia
• Renal Failure, Chronic
• Renal Tubular Acidosis
• Vomiting, Chronic

Abbreviations

• ACE = angiotensin converting enzyme
• ACTH = adrenocorticotropic hormone
• ATPase = adenosine triphosphate
• CO₂ = carbon dioxide
• HCO₃^– = bicarbonate
• K⁺ = potassium
• Na⁺ = sodium
• PU/PD = polyuria/polydipsia