Which of the following cannot be explained by hypokalemia: lower extremity weakness, drowsiness, respiratory rate of 10 breaths per minute, or hypoactive bowel sounds?

Drowsiness Cannot Be Explained by Hypokalemia

Drowsiness is the clinical finding that cannot be explained by hypokalemia. Hypokalemia primarily affects excitable tissues—skeletal muscle, cardiac muscle, and smooth muscle—but does not cause central nervous system depression or altered mental status 1, 2, 3.

Why Each Finding Can or Cannot Be Explained by Hypokalemia

Lower Extremity Weakness: EXPLAINED

• Hypokalemia directly causes skeletal muscle weakness, including flaccid paralysis in severe cases, through impaired muscle membrane excitability 2, 3, 4
• The neuromuscular manifestations include muscle weakness, paresthesias, and depressed deep tendon reflexes 2
• Severe hypokalemia can progress to complete flaccid paralysis and rhabdomyolysis 5, 4

Drowsiness: NOT EXPLAINED

• Hypokalemia does not cause altered mental status, drowsiness, or central nervous system depression 1, 2, 3
• The classic manifestations of hypokalemia involve cardiac arrhythmias, neuromuscular weakness, and gastrointestinal dysmotility—not CNS depression 2, 3, 4
• If drowsiness is present, you must search for alternative explanations such as hypercapnia, metabolic encephalopathy, medication effects, or other electrolyte disturbances 1, 2

Respiratory Rate of 10: EXPLAINED

• Severe hypokalemia causes respiratory muscle weakness, which can lead to hypoventilation and respiratory failure 2, 3
• Respiratory difficulties occur due to weakness of the diaphragm and intercostal muscles 2
• A respiratory rate of 10 breaths per minute represents hypoventilation from respiratory muscle dysfunction, not CNS depression 2, 3

Hypoactive Bowel Sounds: EXPLAINED

• Hypokalemia impairs smooth muscle function throughout the gastrointestinal tract, causing decreased motility 5, 6, 4
• This can manifest as ileus, constipation, and hypoactive bowel sounds 6, 4
• Gastrointestinal complications are well-recognized structural and functional defects caused by potassium deficiency 6

Critical Clinical Distinction

The key differentiating feature is that hypokalemia affects excitable tissues (muscle and cardiac conduction) but does not directly impair consciousness or alertness 1, 2, 3. When you encounter a patient with hypokalemia and drowsiness:

• Investigate concurrent causes such as hypercapnia from respiratory muscle weakness, sepsis, medication effects, or other metabolic derangements 1, 2
• Do not attribute altered mental status to hypokalemia alone—this represents a diagnostic pitfall that can delay recognition of life-threatening conditions 2, 3
• The drowsiness may be a consequence of severe respiratory failure (from hypokalemia-induced muscle weakness causing CO₂ retention), but it is not a direct effect of low potassium on the CNS 2, 3