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USMLE – Hyperkalemia

1. Plasma K+ >5.0 mmol/L (if >7.5 mmol/L, life-threatening)
2. Caused by increased release from cells (intravascular hemolysis, tumor lysis syndrome, rhabdomyloysis); decreased clearance by kidney due to acute or chronic kidney failure; excess intake (often iatrogenic)

Signs and Symptoms
1. Weakness up to flaccid paralysis
2. Cardiac excitability

Characteristic Test Findings
1. Peaked T waves
2. Prolonged PR interval
3. Widening of QRS
4. Absent P waves
5. Ventricular arrhythmias (ventricular tachycardia, ventricular fibrillation)

Associated Conditions
1. Metabolic acidosis (due to intracellular buffering of H+)
2. Hyperglycemia
3. Digitalis toxicity
4. Hemolysis
5. Hyperaldosteronism (Conn’s disease)
6. Addison disease
7. K+ sparing diuretics (spironolactone)
8. ACE inhibitors
10. Cyclosporine
11. Trimethoprim
12. Pentamidine

Hyperkalemia partially depolarizes cardiac cell membranes

1. Aim is to shift K+ into cells and promote K+ loss
2. 25-50 g of Kayexalate (sodium polystyrene sulfonate) with 100 mL of 20% sorbitol by mouth or enema (cation exchange agent)
3. 1 ampule of calcium gluconate (decreases membrane excitability), 50 g IV glucose, and 10-20 units of regular insulin IV (causes K+ to shift into cells)
4. Beta-2-adrenergic agonists via IV or nebulizer (effect lasts 2-4 h)
5. Dialysis with low K+ dialysate
6. Alkali therapy with 3 ampules of NaNCO-3 per liter IV

Tips for USMLE Step 1, Step 2 CK and Step 3
If question mentions peaked T waves on EKG, think hyperkalemia (or anterior cardiac ischemia)

Lillian Thompson By Lillian Thompson

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