A patient with an acute exacerbation of chronic obstructive pulmonary disease (COPD) has an Arterial Blood Gas (ABG) analysis that confirms respiratory acidosis. The nurse anticipates that this acid-base imbalance will most likely cause which corresponding electrolyte disturbance?

1. A

   Hyponatremia

2. B

   Hypercalcemia

3. C

   Hypokalemia

4. D

   Hyperkalemia

Appeared in: NORCET 9 Prelims-2025

Explanation

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• In acute respiratory acidosis, there is an excess of hydrogen ions (H⁺) in the blood, making it acidic.
• The body's immediate buffering system moves these excess H⁺ ions from the blood into the intracellular fluid to reduce the acidity.
• To maintain electrical balance (electroneutrality), for every H⁺ ion that enters a cell, a positively charged potassium ion (K⁺) must leave the cell and enter the bloodstream.
• This shift of potassium from the intracellular to the extracellular space leads to an increase in the serum potassium level, a condition known as hyperkalemia.

Why Other Options Were Wrong

• Option A: Hyponatremia (low sodium) is primarily associated with disturbances in water balance (e.g., SIADH, excessive fluid intake) rather than the primary compensatory shifts of acute respiratory acidosis.
• Option B: Hypercalcemia (high calcium) is not the most likely or immediate electrolyte disturbance. While acidosis can increase the level of ionized (active) calcium, the effect on total serum calcium is minimal and hyperkalemia is a more prominent and clinically significant finding.
• Option C: Hypokalemia (low potassium) is the opposite of what occurs in acidosis. This condition is characteristic of alkalosis.

Related Visual

• Visual 1: Diagram - A simple diagram showing a body cell and the surrounding blood vessel. Arrows should depict H⁺ ions moving from the blood into the cell and K⁺ ions moving from the cell into the blood, with the title 'Ion Exchange in Acidosis'.

Clinical Relevance

• Nursing practice connection: Knowing Relationship between Acid-Base Imbalances and Electrolyte Disturbances helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
• Hyperkalemia is a critical finding because it can cause life-threatening cardiac dysrhythmias, such as peaked T waves, widened QRS complex, and ultimately ventricular fibrillation or asystole.
• Nurses caring for patients with acute respiratory acidosis (e.g., from a COPD exacerbation) must prioritize monitoring serum potassium levels and observing the patient's cardiac rhythm on a heart monitor.
• What if? If the patient's ABG showed respiratory alkalosis instead (e.g., from hyperventilation due to anxiety or pain), the nurse would anticipate the opposite effect: hypokalemia, as K⁺ would shift into the cells.

How to Approach the Question

• First, identify the primary acid-base disorder from the question stem: 'respiratory acidosis'.
• Recall the fundamental principle of how the body buffers acute acidosis at the cellular level.
• Remember the key ion exchange: The body pushes acid (H⁺) into cells to get it out of the blood.
• To maintain electrical balance, a positive ion must come out. The main intracellular positive ion is potassium (K⁺).
• Therefore, acidosis causes K⁺ to shift out of cells, leading to high serum potassium (hyperkalemia).
• Evaluate the options and select the one that matches this physiological process.

Concept Tested & Keywords

• Concept Tested: Relationship between Acid-Base Imbalances and Electrolyte Disturbances
• Stem keywords: chronic obstructive pulmonary disease (COPD), respiratory acidosis, Arterial Blood Gas (ABG), electrolyte disturbance
• Lead-in keywords: most likely cause
• Clinical cues: acute exacerbation
• Clinical cues: respiratory acidosis confirmed by ABG

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