Hyperkalemia
Nephrology
Illness script · Nephrology
Hyperkalemia
Serum potassium >5.5 mEq/L causing life-threatening cardiac and neuromuscular dysfunction via altered membrane potential.
This illness script for Hyperkalemia covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Chronic kidney disease / AKI (most common cause — impaired renal excretion)
- ACE inhibitors, ARBs, potassium-sparing diuretics (spironolactone, triamterene)
- Adrenal insufficiency (aldosterone deficiency)
- Massive tissue destruction: rhabdomyolysis, tumor lysis, hemolysis
- Type IV renal tubular acidosis (hyporeninemic hypoaldosteronism — common in diabetics)
- Pseudohyperkalemia: prolonged tourniquet use, hemolyzed sample — always repeat
02
Presentation
- Often asymptomatic until severe (>6.5 mEq/L)
- Muscle weakness, fatigue, ascending paralysis in severe cases
- Palpitations, bradycardia, cardiac arrest
- ECG changes in order: peaked T waves → prolonged PR → wide QRS → sine wave → VF/asystole
- Peaked (tall, narrow, symmetric) T waves are the earliest ECG finding
- GI symptoms: nausea, cramping, diarrhea
03
Pathophysiology
- ↑ extracellular K⁺ reduces resting membrane potential, making cells less excitable
- Delayed cardiac repolarization → conduction abnormalities and fatal arrhythmias
- In acidosis, H⁺/K⁺ exchange shifts K⁺ extracellularly (~0.6 mEq/L rise per 0.1 pH drop)
- Insulin and catecholamines normally drive K⁺ into cells; their absence worsens hyperkalemia
04
Diagnostics
- Serum BMP: repeat if hemolysis suspected (pseudohyperkalemia)
- 12-lead ECG immediately for all hyperkalemia — guides urgency of treatment
- Urine K⁺, TTKG, aldosterone/renin to evaluate etiology
- ABG: concurrent acidosis shifts K⁺ extracellularly
- BUN/Cr to assess renal function as most common cause
05
Management
- Cardiac membrane stabilization: IV calcium gluconate (or calcium chloride) if ECG changes — acts in minutes
- Redistribute K⁺ into cells: IV insulin + dextrose (onset 15–30 min), albuterol nebulization
- Eliminate K⁺: loop diuretics (if urine output), sodium polystyrene/patiromer/sodium zirconium (GI binding)
- Hemodialysis: definitive, most effective — use for AKI/CKD with refractory or severe hyperkalemia
- Hold offending agents (ACE-I, ARBs, NSAIDs, K⁺-sparing diuretics); restrict dietary K⁺
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Pseudohyperkalemia
No ECG changes; repeat properly collected sample is normal — always verify before treating
Hypokalemia (misread ECG)
Hypokalemia shows U waves and flat T waves; hyperkalemia shows peaked narrow T waves
Addison's Disease
Hyperkalemia + hyponatremia + hypotension + skin hyperpigmentation → check AM cortisol/ACTH stim
Type IV RTA
Hyperkalemia + normal anion gap metabolic acidosis in diabetic/elderly with low aldosterone — no AKI required
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.