Contents
Why Electrolytes Are Heavily Tested
- Electrolyte shifts cause arrhythmias, weakness, seizures, and altered mental status
- The CCRN loves ECG changes and the order of correction
- Potassium and magnesium are the most arrhythmogenic
- Always correct magnesium — you often cannot fix K⁺ or Ca²⁺ until Mg is repleted
Potassium Overview
- Normal: 3.5–5.0 mEq/L — a narrow, dangerous window
- Critical for cardiac membrane stability
- Both high and low K⁺ cause life-threatening arrhythmias
- Acidosis raises serum K⁺; alkalosis and insulin lower it
Hyperkalemia (>5.0)
- Causes: renal failure, acidosis, cell lysis, K⁺-sparing drugs
- ECG: peaked T waves → widened QRS → sine wave → arrest
- Stabilize membrane: IV calcium first if ECG changes
- Shift into cells: insulin + dextrose, albuterol, bicarb (if acidotic)
- Remove: diuretics, GI binders, dialysis
Test what you just learnedJump to CCRN-style practice questions on this topic — instant feedback with full rationales.
Start Free Practice →Hypokalemia (<3.5)
- Causes: diuretics, GI losses (vomiting/diarrhea), alkalosis, poor intake
- ECG: flattened T waves, U waves, ST depression
- Symptoms: muscle weakness, cramps, arrhythmias, ileus
- Replace K⁺ (IV no faster than ~10 mEq/hr peripherally; on a monitor for higher rates) and correct Mg
Sodium Overview
- Normal: 135–145 mEq/L; primarily a WATER balance problem
- Sodium disorders are about free-water excess or deficit
- Mental status changes track the rate of change, not just the number
- Correct slowly to avoid neurologic injury
Hyponatremia (<135)
- Causes: SIADH, heart/liver failure, diuretics, water intoxication
- Symptoms: headache, nausea, confusion, seizures (cerebral edema)
- Correct SLOWLY (≤~8–10 mEq/L per 24 hr)
- Too-rapid correction → osmotic demyelination syndrome
Hypernatremia (>145)
- Usually a free-water DEFICIT (dehydration, diabetes insipidus, poor intake)
- Symptoms: thirst, restlessness, lethargy, seizures
- Replace free water and treat the cause; correct slowly
- Rapid correction can cause cerebral edema
Calcium Imbalances
- Normal ionized Ca²⁺ matters; albumin affects total calcium
- Hypocalcemia: tetany, ↑DTRs, Chvostek & Trousseau signs, prolonged QT, laryngospasm
- Hypercalcemia: weakness, confusion, constipation, shortened QT, stones/bones/groans
- Hypocalcemia is common after massive transfusion (citrate) and in pancreatitis
Magnesium Imbalances
- Hypomagnesemia: arrhythmias (torsades), tremor, refractory hypokalemia/hypocalcemia
- Hypermagnesemia: ↓DTRs, hypotension, respiratory depression, bradycardia
- Give Mg for torsades de pointes
- Calcium gluconate is the antidote for symptomatic hypermagnesemia
ECG Effects & Nursing Priorities
- Peaked T waves = hyperkalemia; U waves = hypokalemia
- Prolonged QT = hypocalcemia / hypomagnesemia (torsades risk)
- Shortened QT = hypercalcemia
- Cardiac monitoring during replacement; recheck levels; correct Mg first
Can you answer these 3 CCRN questions?
Here are 3 questions in the style of our premium bank. The full rationale explains exactly why the right answer is right — and why the distractors trap most test-takers.
Premium Practice Question
A patient with renal failure has a K⁺ of 7.0 with peaked T waves and a widening QRS. The FIRST intervention is:
- Insulin and dextrose
- IV calcium gluconate
- Sodium polystyrene sulfonate
- Albuterol nebulizer
Rationale: With ECG changes from severe hyperkalemia, IV calcium is given first to stabilize the myocardium; shifting and removal therapies follow....
Unlock full rationale + 692 more questions
Premium Practice Question
A patient with chronic hyponatremia (Na⁺ 116) is corrected too quickly. The nurse monitors for:
- Cerebral edema
- Osmotic demyelination syndrome
- Hyperkalemia
- Hypocalcemic tetany
Rationale: Overly rapid correction of chronic hyponatremia can cause osmotic demyelination syndrome; sodium should be raised no more than about 8–10 mEq/L in 24 hours....
Unlock full rationale + 692 more questions
Premium Practice Question
A patient has recurrent torsades de pointes. In addition to defibrillation if pulseless, the priority medication is:
- IV potassium
- IV magnesium sulfate
- IV calcium chloride
- Amiodarone
Rationale: Magnesium sulfate is the treatment of choice for torsades de pointes, which is often associated with hypomagnesemia and a prolonged QT....
Unlock full rationale + 692 more questions
Related CCRN Guides
Frequently Asked Questions
Which electrolyte imbalances are the most dangerous?
Potassium and magnesium disturbances are the most arrhythmogenic and immediately life-threatening. Severe hyperkalemia and hypomagnesemia (torsades) are classic CCRN emergencies.
What are the ECG changes of hyperkalemia and hypokalemia?
Hyperkalemia produces peaked T waves that progress to a widened QRS and a sine-wave pattern. Hypokalemia produces flattened T waves, U waves, and ST depression.
Why must hyponatremia be corrected slowly?
Correcting chronic hyponatremia too quickly (more than about 8–10 mEq/L in 24 hours) can cause osmotic demyelination syndrome, an irreversible neurologic injury. Conversely, correcting hypernatremia too fast risks cerebral edema.
Why is magnesium corrected first?
Low magnesium causes refractory hypokalemia and hypocalcemia, so potassium and calcium often cannot be normalized until magnesium is replaced. Magnesium is also the treatment for torsades de pointes.
What are Chvostek and Trousseau signs?
They are signs of hypocalcemia. Chvostek sign is facial twitching when the facial nerve is tapped; Trousseau sign is carpal spasm when a blood pressure cuff is inflated on the arm.
Want the full CCRN experience?
Practice with 695+ exam-style questions, adaptive flashcards, and AI-powered weak-area drilling inside the Zero Deficit app.
Start Free →