A client has a serum potassium level of 6.8 mEq/L (severe hyperkalemia). Which finding is the nurse's priority concern?

Severe HYPERKALEMIA (normal potassium 3.5-5.0 mEq/L) is a medical emergency because of its effect on the HEART — it causes CARDIAC DYSRHYTHMIAS. ECG changes progress: PEAKED T waves → widened QRS → and potentially fatal arrhythmias (ventricular fibrillation, cardiac arrest/asystole). NCLEX physiological/electrolytes. The cardiac effects make hyperkalemia life-threatening — this is the priority concern. TREATMENT (severe): calcium gluconate (protects the heart), insulin with glucose and/or sodium bicarbonate (shift K+ into cells), and measures to remove potassium (diuretics, dialysis, potassium-binding agents). Causes: renal failure, potassium-sparing diuretics, tissue damage. Recognizing the cardiac danger of hyperkalemia (and its ECG changes) is a heavily tested NCLEX concept.