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Difficulty: MediumPhysiological Adaptation

A nurse is evaluating a client admitted with a severe exacerbation of chronic obstructive pulmonary disease (COPD). The client has become increasingly lethargic over the last hour, is difficult to arouse, and exhibits a shallow respiratory rate of 10 breaths/min. Which of the following arterial blood gas (ABG) results is most consistent with this client's current clinical presentation?

  1. A
    pH 7.37, PaCO2 58 mm Hg, HCO3 33 mEq/L, PaO2 62 mm Hg
  2. B
    pH 7.49, PaCO2 28 mm Hg, HCO3 24 mEq/L, PaO2 70 mm Hg
  3. pH 7.25, PaCO2 78 mm Hg, HCO3 34 mEq/L, PaO2 52 mm HgAnswer
  4. D
    pH 7.28, PaCO2 38 mm Hg, HCO3 15 mEq/L, PaO2 92 mm Hg

Answer

The ABG result showing pH 7.25, PaCO2 78 mm Hg, HCO3 34 mEq/L, and PaO2 52 mm Hg.
The client is hypoventilating (10 breaths/min) and exhibiting signs of CO2 narcosis (lethargy). This acute CO2 retention causes a sharp decrease in pH (acidosis). Because the client has COPD, they already have a baseline of chronically elevated HCO3 to compensate for chronically high CO2. The correct ABG demonstrates this acute uncompensated drop in pH (7.25) superimposed on chronic CO2 retention (78 mm Hg) and elevated bicarbonate (34 mEq/L).

Step-by-Step Solution

1
Analyze the client's clinical presentation.
Lethargy, difficulty to arouse, and a respiratory rate of 10 breaths/min indicate severe hypoventilation and carbon dioxide narcosis.
Identifying the physiological state is required to predict the acid-base imbalance.
2
Determine the expected primary acid-base disorder.
Hypoventilation leads to acute retention of CO2, causing respiratory acidosis (low pH, high PaCO2).
Carbon dioxide acts as an acid in the body; retention directly lowers blood pH.
3
Evaluate the underlying chronic condition (COPD).
Clients with severe COPD typically have chronically elevated PaCO2 and a compensatory high HCO3. An acute exacerbation causes the PaCO2 to spike further, dropping the pH.
Understanding baseline ABG alterations in COPD helps differentiate acute decompensation from chronic stability.
4
Select the ABG matching acute respiratory acidosis on top of chronic compensation.
The result with a low pH (7.25), severely elevated PaCO2 (78 mm Hg), and elevated HCO3 (34 mEq/L) matches this profile.
This is the only option showing an acute acidotic state driven by respiratory failure in a patient with a history of COPD.

Key Concept

In a client with COPD, acute hypoventilation leads to acute respiratory acidosis and CO2 narcosis, manifested by a severe drop in pH and a significant spike in PaCO2 above their already elevated baseline.
Estimated Time:1m 30s
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Physiological Adaptation

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