The nurse would anticipate which of the following ABG results in a client experiencing a prolonged, severe asthma attack?
A. Decreased PaCO2, increased PaO2, and decreased pH.
B. Increased PaCO2, decreased PaO2, and decreased pH.
C. Increased PaCO2, increased PaO2, and increased pH.
D. Decreased PaCO2, decreased PaO2, and increased pH.
Correct Answer: B. Increased PaCO2, decreased PaO2, and decreased pH.
As the severe asthma attack worsens, the client becomes fatigued and alveolar hypotension develops. This leads to carbon dioxide retention and hypoxemia. The client develops respiratory acidosis. Therefore, the PaCO2 level increases, the PaO2 level decreases, and the pH decreases, indicating acidosis.
Option A: Respiratory acidosis is a very common acid-base disturbance in acute severe asthma and is widely considered to be an ominous finding. Its early recognition and treatment are important and decisive for the final outcome, as it can lead to respiratory failure and arrest if prolonged.
Option C: Hypercapnia in asthma, in addition to the severity of the disease, is also associated with the therapeutic administration of oxygen. Thus, in patients with severe asthma exacerbation, a significant increase (?4 mmHg) in transcutaneous PCO2 (PtCO2) was observed in a higher proportion in those receiving high oxygen mixtures (>8 L/min), compared to those who received titrated oxygen (to achieve oxygen saturation of 93–95%)
Option D: Lee et al. noted that PaCO2 was significantly higher and the arterial blood pH lower in asthmatics who died, and delays in providing mechanical ventilation led to worse outcomes. Another mechanism implicates the Haldane effect, in which oxygen displaces the CO2 dissociation curve to the right, increasing PaCO2, which cannot be normalized as patients with severe COPD are unable to increase ventilation.
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