A patient with chronic obstructive pulmonary disease (COPD) undergoes arterial blood gas (ABG) analysis. Which of the following ABG values is most consistent with partially compensated respiratory acidosis?

1. A

   pH 7.35, pCO₂ 49 mmHg, HCO₃⁻ 24 mEq/L

2. B

   pH 7.29, pCO₂ 50 mmHg, HCO₃⁻ 28 mEq/L

3. C

   pH 7.40, pCO₂ 40 mmHg, HCO₃⁻ 24 mEq/L

4. D

   pH 7.48, pCO₂ 30 mmHg, HCO₃⁻ 22 mEq/L

Appeared in: NORCET 10 Mains

Explanation

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• Partially compensated respiratory acidosis is characterized by a pH that is still acidic (less than 7.35), a high pCO₂ (greater than 45 mmHg), and a high HCO₃⁻ (greater than 26 mEq/L).
• The high pCO₂ is the primary respiratory problem, leading to acidosis.
• The high HCO₃⁻ indicates that the kidneys are attempting to compensate by retaining bicarbonate.
• The pH remains below the normal range, which is why the compensation is considered 'partial' and not 'full'.

Why Other Options Were Wrong

• Option A: This represents fully compensated respiratory acidosis. The pCO₂ is high (49 mmHg), but the pH has returned to the normal range (7.35), indicating the body's compensatory mechanisms have successfully balanced the acid-base status.
• Option C: All values (pH 7.40, pCO₂ 40 mmHg, HCO₃⁻ 24 mEq/L) are within the normal range.
• Option D: This represents uncompensated respiratory alkalosis. The pH is high (alkalotic), and the pCO₂ is low, which is the opposite of respiratory acidosis. The bicarbonate level is normal, indicating no compensation has occurred.

Related Visual

• Visual 1: Flowchart: A step-by-step flowchart for ABG interpretation. This would visually guide the learner through checking pH, then pCO₂, then HCO₃⁻ to determine the primary disorder and compensation status.
• Visual 2: Diagram: A tic-tac-toe grid for ABG analysis. This visual method helps organize the pH, pCO₂, and HCO₃⁻ values to quickly identify the acid-base imbalance.

Clinical Relevance

• Nursing practice connection: Knowing ABG interpretation for partially compensated respiratory acidosis helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
• In patients with COPD, chronic respiratory acidosis is a common finding due to impaired gas exchange and CO₂ retention. Nurses must be able to interpret ABGs to assess the severity of an exacerbation and the effectiveness of treatments like controlled oxygen therapy or mechanical ventilation.
• Monitoring for signs of worsening respiratory acidosis (e.g., confusion, lethargy, headache, decreased level of consciousness) is a critical nursing responsibility.
• What if? If the patient's pH was 7.36, pCO₂ was 50 mmHg, and HCO₃⁻ was 29 mEq/L, the condition would be classified as fully compensated respiratory acidosis because the pH has returned to the normal range, even though the other values are abnormal.

How to Approach the Question

• Step 1: Analyze the pH. A value below 7.35 indicates acidosis. A value above 7.45 indicates alkalosis.
• Step 2: Analyze the pCO₂. This represents the respiratory component. A high pCO₂ (greater than 45 mmHg) causes acidosis. A low pCO₂ (less than 35 mmHg) causes alkalosis. Use the ROME mnemonic (Respiratory Opposite) to see if the pH and pCO₂ are moving in opposite directions.
• Step 3: Analyze the HCO₃⁻. This represents the metabolic (renal) component. A low HCO₃⁻ (less than 22 mEq/L) causes acidosis. A high HCO₃⁻ (greater than 26 mEq/L) causes alkalosis. Use the ROME mnemonic (Metabolic Equal) to see if the pH and HCO₃⁻ are moving in the same direction.
• Step 4: Determine the primary disorder by matching the pCO₂ or HCO₃⁻ with the pH.
• Step 5: Assess for compensation. If the component that does not match the pH is abnormal, compensation is occurring. If the pH is still abnormal, it is 'partial' compensation. If the pH has returned to normal, it is 'full' compensation.

Concept Tested & Keywords

• Concept Tested: ABG interpretation for partially compensated respiratory acidosis
• Stem keywords: chronic obstructive pulmonary disease (COPD), arterial blood gas (ABG) analysis, partially compensated respiratory acidosis
• Lead-in keywords: most consistent with
• Clinical cues: Patient with COPD, a condition known to cause chronic CO₂ retention.

Question ID

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