Potassium (K⁺)
Normal: 3.5–5.0 mEq/L
Hypokalemia (<3.5)
Causes: Diuretics (furosemide), vomiting, diarrhea, alkalosis
Signs: Muscle weakness, leg cramps, U waves on ECG, constipation
ECG: Flattened T waves, U waves, ST depression
⚠️ Danger: Cardiac arrest (V-fib)
💊 Treatment: Oral/IV KCl; NEVER IV push; max 10 mEq/hr peripheral; cardiac monitor
Hyperkalemia (>5.0)
Causes: Renal failure, ACE inhibitors, K-sparing diuretics, crush injuries
Signs: Muscle twitching → weakness → paralysis, bradycardia
ECG: Tall peaked T waves, widened QRS, sine wave
⚠️ Danger: Cardiac arrest (asystole)
💊 Treatment: Calcium gluconate, insulin + D50, kayexalate, dialysis
Sodium (Na⁺)
Normal: 136–145 mEq/L
Hyponatremia (<136)
Causes: SIADH, water intoxication, diuretics, heart failure
Signs: Confusion, headache, seizures, muscle cramps, nausea
⚠️ Danger: Cerebral edema, seizures, brain herniation
💊 Treatment: Fluid restriction (SIADH), hypertonic saline 3% (severe) — correct slowly <10-12 mEq/24h
Hypernatremia (>145)
Causes: Dehydration, diabetes insipidus, excessive sodium
Signs: Extreme thirst, dry mucous membranes, agitation, seizures
⚠️ Danger: Brain cell shrinkage, hemorrhage
💊 Treatment: Hypotonic fluids (0.45% NS or D5W); correct slowly
Calcium (Ca²⁺)
Normal: 8.5–10.5 mg/dL
Hypocalcemia (<8.5)
Causes: Hypoparathyroidism, renal failure, post-thyroidectomy
Signs: Trousseau sign, Chvostek sign, tetany, seizures, prolonged QT
ECG: Prolonged QT interval
⚠️ Danger: Laryngospasm, cardiac arrest
💊 Treatment: IV calcium gluconate; oral calcium + vitamin D; seizure precautions
Hypercalcemia (>10.5)
Causes: Hyperparathyroidism, malignancy, immobility
Signs: "Stones, Bones, Groans, Moans" — kidney stones, bone pain, abd pain, confusion
ECG: Shortened QT
⚠️ Danger: Cardiac arrest, renal failure
💊 Treatment: IV NS hydration, loop diuretics, bisphosphonates, calcitonin
Magnesium (Mg²⁺)
Normal: 1.5–2.5 mEq/L
Hypomagnesemia (<1.5)
Causes: Alcoholism, malnutrition, diuretics, diarrhea
Signs: Tremors, hyperreflexia, seizures, dysrhythmias
ECG: Flat T waves, prolonged PR/QT
⚠️ Danger: Torsades de pointes, seizures
💊 Treatment: IV magnesium sulfate; correct Mg BEFORE K will correct
Hypermagnesemia (>2.5)
Causes: Renal failure, excessive MgSO4, antacids
Signs: Hyporeflexia, lethargy, hypotension, respiratory depression
ECG: Prolonged PR, widened QRS
⚠️ Danger: Respiratory arrest, cardiac arrest
💊 Treatment: Stop Mg source, IV calcium gluconate, ventilatory support
Frequently Asked Questions
What ECG changes occur with hyperkalemia?
Tall peaked T waves, widened QRS, eventually sine wave. Can progress to cardiac arrest. Treatment: calcium gluconate, insulin + D50, kayexalate, dialysis.
What ECG changes occur with hypokalemia?
Flattened T waves, U waves, ST depression. Treatment: oral or IV KCl (never IV push; max 10 mEq/hr peripheral) with cardiac monitor.
What are the signs of hypocalcemia?
Trousseau sign, Chvostek sign, tetany, seizures, and prolonged QT. Treatment: IV calcium gluconate plus seizure precautions.
Why must magnesium be corrected before potassium?
Hypomagnesemia blocks the Na-K ATPase pump, so replacing K without correcting Mg causes the K to be wasted. Always check and correct Mg first.