A 72-year-old client with heart failure is receiving captopril 25 mg orally three times daily and spironolactone 25 mg orally daily. The morning labs show serum potassium 5.9 mEq/L (5.9 mmol/L). The client reports muscle weakness and tingling around the mouth. Which action by the nurse takes priority?

ACEi + K-sparing diuretic — hyperkalemia recognition
Captopril (ACEi) reduces aldosterone, decreasing renal K+ excretion. Combined with spironolactone (aldosterone antagonist, K-sparing), the synergistic effect is hyperkalemia — the most common life-threatening interaction in this combination. Normal K+ is 3.5-5.0 mEq/L; 5.9 mEq/L is moderate-to-severe hyperkalemia and the client has classic neuromuscular symptoms (weakness, perioral paresthesia). The greatest immediate risk is cardiac arrhythmia (peaked T waves → wide QRS → VF/asystole). The first nursing action is to obtain continuous cardiac monitoring (12-lead/ECG telemetry) AND notify the provider — these are inseparable in priority. Subsequent provider orders may include holding the offending drugs, calcium gluconate IV (membrane stabilization), insulin + D50 (intracellular shift), and a binder (kayexalate or patiromer) for elimination. Independent kayexalate or banana are not nursing-initiated priorities. Giving the next captopril dose worsens the situation.

Why option 1 is correct
Captopril is an ACE inhibitor that lowers aldosterone, reducing renal potassium excretion. Spironolactone is an aldosterone antagonist and potassium-sparing diuretic. Together they create a synergistic risk for hyperkalemia, the most dangerous interaction in this combination. A potassium of 5.9 mEq/L is moderate-to-severe hyperkalemia, and weakness plus perioral tingling are classic neuromuscular symptoms.

Immediate danger
The priority risk is dysrhythmia: peaked T waves can progress to wide QRS, ventricular fibrillation, or asystole. The nurse should obtain immediate ECG/telemetry and notify the provider. Expected orders may include holding causative drugs, IV calcium gluconate for membrane stabilization, insulin plus D50 to shift potassium intracellularly, and potassium binders for elimination.

Distractor review
Option 2: giving more captopril worsens hyperkalemia. Option 3: bananas add potassium. Option 4: kayexalate alone is not the first independent nursing priority when symptomatic hyperkalemia is present; ECG monitoring and provider notification come first.