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Difficulty: HardPhysiological Adaptation

A client with a documented history of severe chronic obstructive pulmonary disease (COPD) presents to the emergency department with acute confusion and worsening dyspnea. Initial room air arterial blood gas (ABG) values are pH 7.28, PaCO2 66 mm Hg, HCO3 31 mEq/L, and PaO2 52 mm Hg. The healthcare provider prescribes supplemental oxygen at 4 L/min via nasal cannula. One hour later, which of the following repeat ABG results most strongly indicates a life-threatening complication directly caused by the prescribed therapy?

  1. pH 7.19, PaCO2 84 mm Hg, HCO3 32 mEq/L, PaO2 96 mm HgAnswer
  2. B
    pH 7.33, PaCO2 60 mm Hg, HCO3 31 mEq/L, PaO2 65 mm Hg
  3. C
    pH 7.52, PaCO2 42 mm Hg, HCO3 31 mEq/L, PaO2 92 mm Hg
  4. D
    pH 7.27, PaCO2 68 mm Hg, HCO3 30 mEq/L, PaO2 54 mm Hg

Answer

The ABG showing pH 7.19, PaCO2 84 mm Hg, HCO3 32 mEq/L, and PaO2 96 mm Hg.
In clients with severe COPD who chronically retain carbon dioxide, administering excessive supplemental oxygen (resulting here in a PaO2 of 96 mm Hg) can lead to oxygen-induced hypercapnia. This occurs due to a worsening ventilation-perfusion (V/Q) mismatch and the Haldane effect. The resulting acute spike in PaCO2 (from 66 to 84 mm Hg) causes a sharp drop in pH (from 7.28 to 7.19), leading to life-threatening acute respiratory acidosis and potential CO2 narcosis.

Step-by-Step Solution

1
Analyze the client's baseline and underlying condition.
The client has severe COPD with baseline hypercapnia (PaCO2 66) and metabolic compensation (HCO3 31).
Understanding baseline pathophysiology is essential to evaluate the response to clinical interventions.
2
Identify the primary risks of the prescribed intervention.
Providing oxygen at 4 L/min to a severe COPD client risks hyper-oxygenation, which can worsen ventilation-perfusion mismatch and reduce the respiratory drive (Haldane effect).
Oxygen therapy in severe COPD must be carefully titrated, typically aiming for a PaO2 of 60-70 mm Hg or SpO2 88-92%.
3
Evaluate the options for signs of this specific respiratory complication.
The option with an abnormally high PaO2 (96 mm Hg), rapidly rising PaCO2 (84 mm Hg), and dropping pH (7.19) perfectly mirrors oxygen-induced hypercapnia.
This confirms that excessive oxygen has severely compromised the client's ventilation, leading to life-threatening acute-on-chronic respiratory acidosis.

Key Concept

Oxygen-induced hypercapnia in Chronic Obstructive Pulmonary Disease (COPD)
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Topics

Physiological Adaptation

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