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Difficulty: MediumPhysiological Adaptation

A client presents to the emergency department with a severe asthma exacerbation. The initial assessment reveals tachypnea with a respiratory rate of 3434 breaths/min and diffuse wheezing. An initial arterial blood gas (ABG) shows a pH of 7.527.52, PaCO2PaCO_2 of 2828 mm Hg, and HCO3−HCO_3^- of 2424 mEq/L. Two hours later, the client appears drowsy, wheezing is diminished, and the respiratory rate has decreased to 1414 breaths/min. A repeat ABG reveals a pH of 7.317.31, PaCO2PaCO_2 of 5656 mm Hg, and HCO3−HCO_3^- of 2424 mEq/L. Based on these findings, what is the most accurate clinical conclusion?

  1. A
    The client is demonstrating rapid renal compensation to correct the initial respiratory alkalosis.
  2. B
    The client's respiratory status is stabilizing, as evidenced by the decreased respiratory rate and diminished wheezing.
  3. The client is experiencing respiratory muscle fatigue, indicating impending respiratory failure.Answer
  4. D
    The client has developed metabolic acidosis as a complication of the prolonged work of breathing.

Answer

The client is experiencing respiratory muscle fatigue, indicating impending respiratory failure.
The correct answer accurately identifies that the client is tiring out. Initially, the client was hyperventilating (respiratory alkalosis) to maintain oxygenation and overcome airway resistance. The later findings of a low pH (acidosis) and high PaCO2PaCO_2 (hypercapnia), combined with a depressed level of consciousness and a decreased respiratory rate, indicate the respiratory muscles are failing. This causes carbon dioxide to rapidly accumulate, signaling impending respiratory arrest that requires immediate medical intervention, such as intubation and mechanical ventilation.

Step-by-Step Solution

1
Analyze the initial arterial blood gas (ABG) and clinical presentation.
The initial pH is 7.527.52 (alkalotic), PaCO2PaCO_2 is 2828 mm Hg (low), and HCO3−HCO_3^- is 2424 mEq/L (normal).
The client is initially hyperventilating in response to the asthma attack, causing 'blowing off' of carbon dioxide and resulting in respiratory alkalosis.
2
Evaluate the clinical changes and the repeat ABG after two hours.
The client is now drowsy with a decreased respiratory rate. The repeat ABG shows a pH of 7.317.31 (acidotic), PaCO2PaCO_2 of 5656 mm Hg (high), and HCO3−HCO_3^- of 2424 mEq/L (normal).
The client is now retaining carbon dioxide, which has led to uncompensated respiratory acidosis.
3
Correlate the laboratory findings with the clinical picture to draw a conclusion.
The transition from hyperventilation to hypoventilation, along with drowsiness and diminished wheezing, indicates respiratory muscle fatigue.
The client is exhausted and no longer able to maintain the effort required to breathe against airway resistance, leading to CO2 accumulation and impending respiratory failure.

Key Concept

In an acute asthma exacerbation, a transition from respiratory alkalosis (hyperventilation) to respiratory acidosis (carbon dioxide retention), accompanied by a decreasing respiratory rate, diminished wheezing, and drowsiness, is an ominous clinical sign indicating severe respiratory muscle fatigue and impending respiratory failure.
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Topics

Physiological Adaptation

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