NCLEX-RNPhysiological AdaptationMedium
A client recovering from severe diarrhea for the past 3 days reports generalized muscle weakness and leg cramps. The nurse notes hypoactive bowel sounds and an ECG showing flattened T waves with a prominent U wave. Which laboratory finding does the nurse expect?
- ASerum sodium of 152 mEq/L
- BSerum calcium of 12.0 mg/dL
- CSerum potassium of 2.9 mEq/L
- DSerum magnesium of 3.0 mg/dL
Show answer & explanationAnswer & explanation
Correct answer: C. Serum potassium of 2.9 mEq/L
Prolonged diarrhea causes significant potassium loss through the GI tract, leading to hypokalemia. Classic manifestations include muscle weakness, hypoactive bowel sounds/ileus, and ECG changes of flattened T waves with a U wave; normal serum potassium is 3.5–5.0 mEq/L, so 2.9 mEq/L is low.
Why the other options are wrong
- A. Hypernatremia causes thirst and neurologic changes, not this ECG pattern.
- B. Hypercalcemia causes constipation and shortened QT, not U waves.
- D. Elevated magnesium causes decreased reflexes and would not cause U waves.
Hypokalemia
Serum potassium below 3.5 mEq/L, often from GI losses, diuretics, or shifting into cells, causing muscle weakness and cardiac dysrhythmias.
- ECG: flattened T waves, prominent U waves, ST depression
- Causes: diarrhea, vomiting, diuretics, insulin administration
- Risk: paralytic ileus and life-threatening dysrhythmias
Memory trick: Low K = Ugly U waves and lazy bowels