Guide — Electrolytes
Electrolyte Imbalance Recognition
Electrolyte imbalances are among the most common and clinically significant findings nurses encounter. Early recognition of abnormal patterns in vital signs, symptoms, and ECG changes allows for timely intervention and prevents life-threatening complications.
11 min read · Electrolytes
Educational use only. Electrolyte abnormalities require laboratory confirmation and provider notification. Treatment thresholds and replacement protocols vary by institution and patient-specific factors. Always follow facility policy and provider orders. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Overview
Electrolytes are minerals that carry electrical charges essential for cell membrane function, fluid balance, nerve conduction, and muscle contraction. Imbalances in even a single electrolyte can produce symptoms affecting multiple organ systems simultaneously.
Key electrolytes to recognize at the bedside:
- Potassium (K⁺): Critical for cardiac rhythm and muscle function — small changes in serum level produce significant clinical effects
- Sodium (Na⁺): Governs osmolality and fluid distribution — imbalances cause neurological symptoms
- Calcium (Ca²⁺): Essential for muscle contraction, nerve conduction, and coagulation
- Magnesium (Mg²⁺): Co-factor for hundreds of enzymes; hypomagnesemia frequently co-occurs with and perpetuates hypokalemia
Potassium (K⁺) — Normal: 3.5 – 5.0 mEq/L
| Hypokalemia (< 3.5) | Hyperkalemia (> 5.0) | |
|---|---|---|
| Causes | Vomiting, diarrhea, NG suction, diuretics (loop/thiazide), insulin, alkalosis, poor intake | Renal failure, acidosis, ACE inhibitors/ARBs, potassium-sparing diuretics, crush injury, hemolysis, K⁺ supplements |
| Symptoms | Muscle weakness, fatigue, leg cramps, ileus, polyuria, hypoactive reflexes | Muscle weakness, paresthesias, nausea, bradycardia, peaked T waves, cardiac arrest (severe) |
| ECG Changes | Flattened/inverted T waves, U wave prominence, ST depression, prolonged QU interval | Peaked (tall, narrow) T waves, widened QRS, sine wave pattern, PEA, ventricular fibrillation |
| Priority Actions | Oral or IV K⁺ replacement per order; correct concurrent hypomagnesemia; cardiac monitoring; fall precautions | Cardiac monitoring; calcium gluconate (stabilize); insulin + dextrose (shift K⁺ intracellularly); Kayexalate/dialysis (eliminate); notify provider immediately |
Critical values: K⁺ < 2.5 mEq/L or > 6.5 mEq/L require immediate provider notification and cardiac monitoring. Hypokalemia and hypomagnesemia frequently co-occur — check and replace magnesium concurrently.
Sodium (Na⁺) — Normal: 136 – 145 mEq/L
| Hyponatremia (< 136) | Hypernatremia (> 145) | |
|---|---|---|
| Causes | SIADH, excessive free water intake, heart failure, cirrhosis, hypothyroidism, diuretics | Dehydration, insufficient water intake, diabetes insipidus, excessive hypertonic fluid, diarrhea (in infants) |
| Symptoms | Headache, nausea, confusion, seizures, coma (severe) — brain swells as water moves into cells | Intense thirst, dry mucous membranes, agitation, confusion, seizures, coma — brain cells shrink |
| Priority Actions | Fluid restriction; hypertonic saline (3%) only for severe/symptomatic; correct slowly (max 8–10 mEq/L per 24 hr) to prevent osmotic demyelination | Free water replacement (D5W or hypotonic saline); correct slowly (max 10 mEq/L per 24 hr) to prevent cerebral edema; monitor neuro status |
Both hyponatremia and hypernatremia correction must be gradual — rapid correction of either disorder causes serious neurological complications. The brain adapts to gradual changes; rapid osmotic shifts cause brain damage.
Calcium (Ca²⁺) — Normal Total: 8.5 – 10.5 mg/dL; Ionized: 4.5 – 5.5 mg/dL
| Hypocalcemia (< 8.5) | Hypercalcemia (> 10.5) | |
|---|---|---|
| Causes | Hypoparathyroidism, post-thyroidectomy, vitamin D deficiency, pancreatitis, alkalosis, hypomagnesemia, massive blood transfusions (citrate binding) | Hyperparathyroidism, malignancy (bone metastases, PTHrP), prolonged immobilization, vitamin D toxicity, thiazide diuretics, sarcoidosis |
| Symptoms | Muscle cramps, tetany, perioral/extremity tingling, seizures, laryngospasm, positive Chvostek's and Trousseau's signs, prolonged QT | “Bones, stones, groans, psychic moans” — bone pain, kidney stones, constipation/nausea, confusion/depression, shortened QT, hypertension |
| ECG Changes | Prolonged QT interval (risk for torsades de pointes) | Shortened QT interval, bradycardia, heart block |
| Priority Actions | IV calcium gluconate for symptomatic hypocalcemia; oral calcium/vitamin D for mild; cardiac monitoring (QT interval); seizure precautions; Trousseau's and Chvostek's testing | IV normal saline hydration; loop diuretics to promote calciuresis; bisphosphonates for malignancy-related; treat underlying cause; monitor cardiac rhythm |
Ionized calcium is the physiologically active form. Alkalosis decreases ionized calcium even with normal total calcium levels — causing symptoms of hypocalcemia in alkalotic patients.
Magnesium (Mg²⁺) — Normal: 1.7 – 2.2 mg/dL
| Hypomagnesemia (< 1.7) | Hypermagnesemia (> 2.2) | |
|---|---|---|
| Causes | Alcoholism, malnutrition, diarrhea, prolonged diuretic use, malabsorption, DKA treatment, PPIs (long-term) | Renal failure (most common), excessive Mg²⁺ replacement, antacid/laxative overuse (especially in elderly), eclampsia treatment overdose |
| Symptoms | Muscle tremors, twitching, tetany, seizures, positive Chvostek's/Trousseau's; refractory hypokalemia and hypocalcemia; torsades de pointes (ventricular arrhythmia) | Flushing, nausea, decreased reflexes (loss of patellar reflex is early warning sign), respiratory depression, bradycardia, cardiac arrest (severe) |
| Priority Actions | IV or oral magnesium replacement per order; assess and replace concurrent hypokalemia and hypocalcemia (often co-present); cardiac monitoring | Stop Mg²⁺ sources; IV calcium gluconate (antidote — stabilizes cardiac membrane); furosemide to enhance excretion; dialysis for severe cases; assess reflexes and respiratory status serially |
Clinical key: hypomagnesemia causes refractory hypokalemia — potassium cannot be maintained until magnesium is repleted. Always check and correct magnesium when replacing potassium in hypokalemic patients.
NCLEX Pearls
- Hyperkalemia + peaked T waves = cardiac emergency — calcium gluconate first, then insulin/glucose to shift K⁺ intracellularly
- Hypokalemia + U waves on ECG = classic NCLEX finding — assess for concurrent alkalosis and diuretic use
- Hypocalcemia + positive Trousseau's (carpal spasm with BP cuff) or Chvostek's (facial twitch with cheek tap) = neuromuscular irritability from low ionized calcium
- Hypomagnesemia causes refractory hypokalemia — you cannot fix the potassium until the magnesium is replaced
- Hypermagnesemia antidote: calcium gluconate (same as hyperkalemia — calcium stabilizes cardiac membranes)
- Rapid correction of hyponatremia → osmotic demyelination syndrome (central pontine myelinolysis) — correct no faster than 8–10 mEq/L per 24 hours
- Hypercalcemia memory aid: “Bones, stones, groans, and psychic moans”
- Alkalosis drives potassium and calcium into cells, reducing serum levels of both — check electrolytes when alkalosis is present
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with Infusion Nurses Society (INS) Standards of Practice · Institute for Safe Medication Practices (ISMP) · Standard laboratory reference ranges. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →