🫀 Physiological Adaptation · Lesson 1 of 10 · 7 min

Potassium: The Electrolyte That Stops Hearts

🍌 Potassium is the one electrolyte with a lethal range on both ends. Too low and the heart quivers; too high and it stops. The exam asks about both, usually in the same client.

💡 Key idea

High potassium: peaked T waves; calcium gluconate protects the heart, insulin and dextrose shift it, binders and dialysis remove it. Low potassium: flat T and U waves, digoxin toxicity risk; replace slowly, never IV push.

🧠 Why it matters

Normal potassium is 3.5 to 5.0 mEq/L. HYPERKALEMIA (above 5.0) comes from kidney failure, potassium-sparing diuretics, ACE inhibitors, acidosis, crushed tissue, burns and transfusions of older blood. ECG shows tall PEAKED T WAVES, then a widened QRS and finally a sine wave and arrest; muscle weakness and paresthesias accompany it. Treatment: IV CALCIUM GLUCONATE to stabilize the heart (it does not lower potassium), then IV REGULAR INSULIN WITH DEXTROSE and nebulized albuterol to shift potassium into cells, sodium bicarbonate if acidotic, and potassium binders, loop diuretics or dialysis to remove it; stop all potassium intake. HYPOKALEMIA (below 3.5) comes from loop and thiazide diuretics, vomiting, diarrhea, nasogastric suction and insulin; ECG shows FLATTENED T waves and U WAVES, with muscle weakness, cramps, constipation, ileus and a dangerously increased sensitivity to DIGOXIN. Replace orally with food, or IV diluted by pump at no more than about 10 mEq/hr peripherally, never by push, and check that the client has adequate urine output first. Teach high-potassium foods: bananas, oranges, potatoes, tomatoes, spinach, avocados and dried fruit.

🏥 In the real world

📈 A client with kidney failure misses dialysis for a week and arrives weak with a potassium of 7.1 and peaked T waves on the monitor. The nurse hangs calcium gluconate first, then insulin with dextrose, while dialysis is arranged. Calcium buys minutes, insulin buys hours, dialysis fixes the problem. The exam asks which comes first, and the answer is the drug that keeps the heart beating.

📌 Takeaways

Normal 3.5 to 5.0; both directions cause arrhythmias
Hyperkalemia: calcium gluconate, insulin plus dextrose, binders, dialysis
Hypokalemia: watch digoxin clients; replace by pump, never push

📖 Terms in this lesson

Hyperkalemia: Potassium above 5.0 mEq/L, which shows as peaked T waves and can stop the heart.

Hypokalemia: Potassium below 3.5 mEq/L, which shows as flat T waves and U waves and raises digoxin toxicity risk.

MURDER (hyperkalemia signs): Muscle weakness, Urine output low, Respiratory distress, Decreased cardiac contractility, ECG changes (peaked T waves), Reflexes abnormal: the signs of potassium above 5.0 mEq/L.

Potassium (K+): Normal 3.5 to 5.0 mEq/L; low brings flat T waves, U waves and digoxin toxicity, high brings peaked T waves and arrest, and below 2.5 or above about 6.0 to 6.5 is critical.

✅ Test yourself

A client with a potassium level of 6.8 mEq/L has peaked T waves. Which medication does the nurse expect to give FIRST?

Oral furosemide
IV calcium gluconate
Subcutaneous insulin
Oral potassium binder

Answer: B · IV calcium gluconate

Calcium gluconate stabilizes the cardiac membrane immediately, preventing arrhythmias while other measures lower the potassium.

A client taking furosemide and digoxin has a potassium of 2.9 mEq/L. Why is this finding especially dangerous?

Low potassium potentiates digoxin
Low potassium causes hyperglycemia
Low potassium is not clinically significant
Low potassium blocks the effect of furosemide

Answer: A · Low potassium potentiates digoxin

Hypokalemia potentiates digoxin, raising toxicity risk even at normal digoxin levels.

Which ECG change is most characteristic of hypokalemia?

Flattened T waves with U waves
Tall peaked T waves
Widened QRS complex
Shortened QT interval

Answer: A · Flattened T waves with U waves

Flattened T waves and the appearance of U waves are classic for low potassium; peaked T waves indicate high potassium.

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