Hyperkalemia Emergency: ECG Changes, Calcium Gluconate, and Rescue Protocol

Potassium is the primary intracellular cation, with approximately 98% of total body potassium residing inside cells. The normal serum potassium range in dogs and cats is 3.5-5.5 mEq/L. This narrow extracellular concentration is tightly regulated by the Na+/K+-ATPase pump, renal excretion (principal cells of the collecting duct), aldosterone, insulin, and acid-base status.

The ratio of intracellular to extracellular potassium determines the resting membrane potential of excitable cells, particularly cardiomyocytes. Even small changes in extracellular K+ concentration can have profound effects on cardiac conduction, making hyperkalemia a true cardiotoxic emergency.

Understanding the underlying cause is essential for definitive treatment. The major categories include:

Decreased renal excretion: Urinary obstruction (the single most common cause in cats), anuric or oliguric acute kidney injury, bilateral ureteral obstruction, ruptured bladder (uroabdomen), and hypoadrenocorticism (Addison's disease) with mineralocorticoid deficiency.

Transcellular shift: Metabolic acidosis (H+ moves intracellularly, K+ moves out), massive tissue injury or crush syndrome, reperfusion injury, and tumor lysis syndrome.

Iatrogenic: Excessive potassium supplementation, potassium-sparing diuretics (spironolactone), ACE inhibitors in patients with renal disease, and administration of stored packed red blood cells (potassium leaks from aging RBCs).

The ECG changes of hyperkalemia follow a predictable, progressive pattern that correlates roughly with serum potassium concentration. Recognizing these changes enables rapid intervention before cardiac arrest.

It is critical to understand that individual variation exists; some patients develop life-threatening arrhythmias at K+ levels that others tolerate. The rate of rise matters as much as the absolute value. Acute hyperkalemia is far more dangerous than chronic hyperkalemia at the same concentration.

Treatment of severe hyperkalemia follows a systematic, time-sensitive protocol with three goals: cardioprotection, intracellular potassium shifting, and potassium elimination.

Step 1 — Calcium Gluconate 10% (Cardioprotection): Administer 0.5-1.0 mL/kg IV slowly over 10-15 minutes with continuous ECG monitoring. Calcium raises the threshold potential of cardiomyocytes, restoring the difference between resting and threshold potentials. It does NOT lower serum potassium; it buys time (approximately 20-30 minutes of cardioprotection). If bradycardia worsens during infusion, stop and reassess.

Step 2 — Regular Insulin + Dextrose (Intracellular Shift): Administer regular insulin at 0.25-0.5 U/kg IV followed by a dextrose bolus of 1-2 g per unit of insulin given (typically 50% dextrose diluted 1:2). Insulin activates the Na+/K+-ATPase, driving potassium intracellularly. Onset is within 15-30 minutes; effect lasts 4-6 hours. Monitor blood glucose closely.

Step 3 — Sodium Bicarbonate (If Acidotic): If metabolic acidosis is present (pH <7.2), administer sodium bicarbonate 1-2 mEq/kg IV slowly over 15-20 minutes. Alkalinization drives H+ out of cells and K+ into cells. Do not use empirically without documented acidosis.

Step 4 — IV Fluid Therapy (Dilution + Renal Excretion): Initiate 0.9% NaCl at a volume and rate appropriate for the patient. Crystalloid fluids dilute serum K+ and promote renal potassium excretion. Avoid lactated Ringer's solution, which contains 4 mEq/L potassium.

Step 5 — Treat the Underlying Cause: Relieve urinary obstruction, treat Addison's crisis with dexamethasone and DOCP, address acute kidney injury, or manage uroabdomen surgically.

After initial stabilization, recheck electrolytes every 1-2 hours until potassium normalizes. Continuous ECG monitoring is essential during the acute phase. Monitor blood glucose every 30-60 minutes after insulin administration to detect and treat hypoglycemia. Once K+ is below 6.0 mEq/L and ECG changes have resolved, transition to maintenance monitoring every 4-6 hours.

Use the Potassium Sliding Scale Calculator to determine appropriate supplementation rates once potassium normalizes and the patient transitions to maintenance fluid therapy, as post-correction hypokalemia is common.

Feline urethral obstruction is the most common cause of severe hyperkalemia in small animal emergency practice. Approximately 71% of blocked cats present with hyperkalemia, and up to 12% have K+ levels above 8.0 mEq/L. The approach is: stabilize first, unblock second. Administer calcium gluconate and begin IV fluids before attempting catheterization. Many severely hyperkalemic cats require 15-30 minutes of stabilization before they are safe for sedation and catheterization.