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 defined by a low pH (acidosis), a high pCO2 (the respiratory cause), and a high HCO3− (the metabolic compensation).
• The pH of 7.29 is below the normal range of 7.35-7.45, indicating acidosis.
• The pCO2 of 50 mmHg is above the normal range of 35-45 mmHg, indicating the primary problem is respiratory acidosis, common in COPD due to inadequate CO2 removal.
• The HCO3− of 28 mEq/L is above the normal range of 22-26 mEq/L, showing that the kidneys are retaining bicarbonate to buffer the acid.
• Since the pH has not yet returned to the normal range despite the elevated bicarbonate, the compensation is considered 'partial'.

Why Other Options Were Wrong

• Option A: This represents fully compensated respiratory acidosis. The pH (7.35) has returned to the low end of the normal range, indicating that the body's compensatory mechanisms have successfully balanced the high pCO2.
• Option C: All values (pH 7.40, pCO2 40 mmHg, HCO3− 24 mEq/L) are within their respective normal ranges. This represents a normal ABG result.
• Option D: This represents uncompensated respiratory alkalosis. The pH (7.48) is high (alkalotic), and the pCO2 (30 mmHg) is low, which is the opposite of acidosis. The bicarbonate level is normal, indicating no compensation has occurred.

Related Visual

Clinical Relevance

• Nursing practice connection: Knowing Interpretation of Arterial Blood Gas (ABG) values for acid-base imbalances, specifically partially compensated respiratory acidosis helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
• For nurses caring for patients with COPD, recognizing the signs of respiratory acidosis is critical. Changes in mental status, such as confusion, lethargy, or somnolence, can indicate rising CO2 levels and worsening acidosis, requiring immediate intervention.
• Nursing interventions for a patient with partially compensated respiratory acidosis focus on improving ventilation. This includes encouraging deep breathing and coughing, administering bronchodilators, providing supplemental oxygen as prescribed (cautiously, to avoid suppressing the hypoxic drive), and positioning the patient to maximize lung expansion (e.g., high-Fowler's position).
• What if? If the patient's ABG showed a pH of 7.36, pCO2 of 60 mmHg, and HCO3− of 34 mEq/L, the condition would be classified as fully compensated chronic respiratory acidosis. The pH is within the normal range, indicating the kidneys have had sufficient time to retain enough bicarbonate to completely buffer the chronically elevated CO2.

How to Approach the Question

• First, recall the normal ranges for ABG values: pH (7.35-7.45), pCO2 (35-45 mmHg), and HCO3− (22-26 mEq/L).
• Analyze the term 'partially compensated respiratory acidosis'. 'Respiratory' means the pCO2 is the cause. 'Acidosis' means the pH is low (<7.35) and the pCO2 is high (>45). 'Partially compensated' means the body is trying to fix it (elevated HCO3− >26), but the pH is not yet normal.
• Step 1: Look at the pH. A value of 7.29 is acidotic.
• Step 2: Look at the pCO2 and HCO3− to determine the cause. The pCO2 is 50 mmHg (high), which matches a respiratory cause for acidosis. The HCO3− is 28 mEq/L (high), which indicates metabolic compensation.
• Step 3: Determine the level of compensation. Since the pH is still abnormal (acidotic) despite the high HCO3−, the compensation is partial.
• Evaluate each option against these criteria. Only the values in option B (pH 7.29, pCO2 50, HCO3− 28) fit the complete picture of partially compensated respiratory acidosis.

Concept Tested & Keywords

• Concept Tested: Interpretation of Arterial Blood Gas (ABG) values for acid-base imbalances, specifically partially compensated respiratory acidosis.
• Stem keywords: chronic obstructive pulmonary disease (COPD), arterial blood gas (ABG), partially compensated respiratory acidosis
• Lead-in keywords: most consistent with
• Clinical cues: The patient has COPD, a condition that predisposes them to retaining CO2, leading to chronic respiratory acidosis.

Question ID

QKTpYDtAtUgvSuZ7gdfL6r

Copy ID

Reference Book

E6 Nursing Fundamentals Potter Perry 12e Part 5 p. 56-58

E6 Nursing Fundamentals Taylor p. 785-787