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Difficulty: HardPhysiological Adaptation

An emergency department nurse is evaluating a young adult who presented with a severe acute asthma exacerbation. Upon arrival, the client exhibited audible wheezing, prominent intercostal retractions, and a respiratory rate of 36 breaths/min. The baseline arterial blood gas (ABG) results on room air were:

ParameterValue
pH7.50
PaCO226 mm Hg
HCO323 mEq/L
PaO270 mm Hg

One hour after the administration of continuous nebulized bronchodilators and intravenous corticosteroids, the nurse reassesses the client. The client is now lethargic, the respiratory rate has decreased to 12 breaths/min, and lung sounds are significantly diminished bilaterally with no audible wheezing. The repeat ABG results are:

ParameterValue
pH7.27
PaCO264 mm Hg
HCO324 mEq/L
PaO252 mm Hg

Which intervention is the most appropriate priority action based on these clinical changes?

  1. Alert the healthcare provider and prepare the airway equipment for immediate intubation and mechanical ventilation.Answer
  2. B
    Continue the current treatment plan and document the clinical improvement in respiratory rate and work of breathing.
  3. C
    Administer a prescribed dose of intravenous sodium bicarbonate to reverse the developing metabolic acidosis.
  4. D
    Switch the oxygen delivery to a non-rebreather mask at 15 L/min and draw a third ABG sample in one hour.

Answer

Alert the healthcare provider and prepare the airway equipment for immediate intubation and mechanical ventilation.
The correct action is to prepare for immediate intubation and mechanical ventilation. During a severe asthma exacerbation, a shift from respiratory alkalosis (due to hyperventilation) to respiratory acidosis (rising PaCO2, falling pH) signals that the client has exhausted their respiratory muscles and can no longer maintain adequate ventilation. The physical signs of lethargy, a normalized or slow respiratory rate, and a lack of wheezing ('silent chest') confirm impending respiratory failure and the critical need for an advanced airway.

Step-by-Step Solution

1
Analyze the initial ABG and clinical presentation.
The client initially presented in respiratory alkalosis (pH 7.50, low PaCO2) due to hyperventilation, which is a common early compensatory mechanism to overcome airway resistance in an asthma attack.
Understanding the baseline establishes the trajectory of the client's respiratory status.
2
Analyze the follow-up ABG results.
The repeat ABG shows uncompensated respiratory acidosis (pH dropped to 7.27, PaCO2 sharply rose to 64 mm Hg) and worsening hypoxemia (PaO2 52 mm Hg).
Identifying the acid-base shift is critical to recognizing alveolar hypoventilation.
3
Correlate the laboratory findings with the physical assessment.
The lethargy, decreased respiratory rate, and absence of wheezing ('silent chest') perfectly align with the hypercapnia. The client's respiratory muscles have fatigued, resulting in an inability to move air.
Clinical assessment validates the lab values and reveals the severity of the decompensation.
4
Determine the highest priority nursing intervention.
Immediate endotracheal intubation and mechanical ventilation are required because the client is in acute respiratory failure and can no longer maintain their own airway or ventilation.
Airway and breathing are the highest priorities; without mechanical support, the client will progress to cardiac arrest.

Key Concept

Recognition of impending respiratory failure and 'silent chest' in acute asthma exacerbation.
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Topics

Physiological Adaptation

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