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Difficulty: MediumReduction of Risk Potential

A client with a documented history of severe chronic obstructive pulmonary disease (COPD) is brought to the emergency department by a caregiver. The caregiver reports that the client has become increasingly lethargic and confused over the past four hours. The healthcare provider orders an arterial blood gas (ABG) analysis on room air. Which of the following ABG results indicates an acute loss of compensatory mechanisms requiring immediate airway management?

  1. A
    pH 7.36, PaCO2PaCO_2 64 mm Hg, HCO3−HCO_3^- 35 mEq/L, PaO2PaO_2 60 mm Hg
  2. B
    pH 7.48, PaCO2PaCO_2 32 mm Hg, HCO3−HCO_3^- 24 mEq/L, PaO2PaO_2 68 mm Hg
  3. pH 7.24, PaCO2PaCO_2 76 mm Hg, HCO3−HCO_3^- 29 mEq/L, PaO2PaO_2 52 mm HgAnswer
  4. D
    pH 7.28, PaCO2PaCO_2 38 mm Hg, HCO3−HCO_3^- 17 mEq/L, PaO2PaO_2 85 mm Hg

Answer

The ABG result showing pH 7.24, PaCO2PaCO_2 76 mm Hg, HCO3−HCO_3^- 29 mEq/L, and PaO2PaO_2 52 mm Hg indicates an acute loss of compensatory mechanisms.
The correct answer demonstrates acute-on-chronic respiratory acidosis. The client's pH is significantly acidotic (7.24) combined with severe hypercapnia (PaCO2PaCO_2 76 mm Hg). While the bicarbonate (HCO3−HCO_3^-) is slightly elevated (29 mEq/L), reflecting underlying chronic compensation from long-standing COPD, it is entirely insufficient to buffer the acute spike in carbon dioxide. This uncompensated state, combined with the clinical presentation of lethargy and confusion, strongly suggests carbon dioxide narcosis and impending respiratory arrest.

Step-by-Step Solution

1
Analyze the client's clinical presentation and medical history.
The client has severe COPD (chronic CO2CO_2 retainer) and presents with new-onset lethargy and confusion.
Lethargy and confusion in a COPD client are classic signs of carbon dioxide narcosis, indicating an acute inability to ventilate adequately.
2
Evaluate the ABG options for signs of acute-on-chronic respiratory failure.
Identify the set of values showing a significantly acidotic pH and an acutely elevated PaCO2PaCO_2 that exceeds the buffering capacity of the chronically elevated HCO3−HCO_3^-.
A client with severe COPD typically operates in a state of fully compensated respiratory acidosis (normal pH, high PaCO2PaCO_2, high HCO3−HCO_3^-). An acute exacerbation causes a sudden spike in PaCO2PaCO_2, causing the pH to drop dramatically because the kidneys cannot increase HCO3−HCO_3^- fast enough to compensate.
3
Select the ABG matching the uncompensated acute decline.
The correct ABG shows a pH of 7.24 (acidemia), a PaCO2PaCO_2 of 76 mm Hg (severe hypercapnia), and an HCO3−HCO_3^- of 29 mEq/L (inadequate chronic compensation for the acute event).
This specific combination confirms a life-threatening respiratory failure requiring immediate intervention, distinguishing it from the client's expected baseline.

Key Concept

Interpretation of Arterial Blood Gases (ABGs) in Acute-on-Chronic Respiratory Failure
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Topics

Reduction of Risk Potential

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