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Difficulty: MediumReduction of Risk Potential

A 58-year-old client is admitted with a severe acute asthma exacerbation. The client is diaphoretic, restless, and using accessory muscles to breathe. The nurse reviews two sets of arterial blood gas (ABG) results drawn two hours apart on room air:

Initial ABG: pH 7.51, PaCO2 28 mm Hg, PaO2 74 mm Hg
Current ABG: pH 7.37, PaCO2 44 mm Hg, PaO2 59 mm Hg

Based on these clinical findings and the ABG trend, which action should the nurse anticipate immediately to reduce the risk of a severe physiological complication?

  1. Preparing the client for immediate endotracheal intubation and mechanical ventilationAnswer
  2. B
    Initiating a rapid intravenous fluid bolus to treat impending hypovolemic shock
  3. C
    Documenting the values as clinical improvement and continuing current therapies
  4. D
    Positioning the client flat in a supine position to promote uniform gas exchange

Answer

The correct action is to prepare the client for immediate endotracheal intubation and mechanical ventilation.
The initial ABG demonstrated respiratory alkalosis, which is an expected compensatory response to hypoxemia in early asthma attacks as the client hyperventilates. However, the subsequent ABG shows a rising PaCO2 (now 44 mm Hg) and a falling pH (7.37), despite continued severe clinical distress. This phenomenon, known as 'pseudonormalization', indicates that the client's respiratory muscles are severely fatigued and they are no longer able to maintain the excessive work of breathing. This is a critical warning sign of impending acute respiratory failure and respiratory arrest. The nurse must immediately prepare to secure the airway through intubation and mechanical ventilation to reduce the risk of a fatal outcome.

Step-by-Step Solution

1
Analyze the initial ABG results.
The initial results show a high pH and low PaCO2, indicating respiratory alkalosis.
This is a normal compensatory mechanism during an early asthma attack as the client hyperventilates to maintain oxygenation.
2
Analyze the current ABG results in relation to the client's physical presentation.
The current results show a 'normal' pH (7.37) and PaCO2 (44 mm Hg), but a worsening PaO2 (59 mm Hg), while the client remains in severe physical distress.
Contextualizing lab values with physical assessment is essential for accurate clinical judgment.
3
Synthesize the data to determine the physiological state.
The rising PaCO2 indicates the client is losing the ability to hyperventilate due to severe respiratory muscle fatigue (pseudonormalization).
If the asthma were resolving, the physical distress would also be subsiding. Persistent distress with rising CO2 means impending respiratory failure.

Key Concept

Pseudonormalization of ABGs in Asthma
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Topics

Reduction of Risk Potential

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