A client is in danger of respiratory arrest following the administration of a narcotic analgesic. An arterial blood gas value is obtained. The nurse would expect PaCO2 to be which of the following values?
A. 15 mm Hg
B. 30 mm Hg
C. 40 mm Hg
D. 80 mm Hg
Correct Answer: D. 80 mm Hg
A client about to go into respiratory arrest will have inefficient ventilation and will be retaining carbon dioxide. The value expected would be around 80 mm Hg. All other values are lower than expected. When shunt is predominant above other mechanisms, the hypoxemia is more severe and refractory to oxygen therapy, meaning that high levels of inspiratory oxygen fraction (FIO2 >50-60%) are needed to reach PaO2 values between 60 and 70mmHg, as in ARDS.
Option A: In cases of significant alveolar dead space (large areas of pulmonary parenchyma without perfusion), such as in pulmonary emphysema, there may be both hypoxemia and hypercapnia due to alveolar hypoventilation and V/Q mismatch, especially if the ventilatory pump could not compensate the baseline disturb.
Option B: The hypoxic ARF is defined by PaO2 levels < 55-60mmHg, in-room air or with indication for oxygen therapy with no CO2 retention. The pulmonary causes of hypoxemia or hypercapnia include dead space, impairment of gas diffusion, V/Q mismatch, and shunt. It is not always possible to determine which is the predominant mechanism in a clinical scenario. Different levels of V/Q disorders may coexist in the patient’s pulmonary parenchyma.
Option C: The hypercapnic ARF is characterized by increased PaCO2 levels above 45-50mHg with resultant acidemia; pH<7.34. The hypercapnic ARF is invariably associated with alveolar hypoventilation with resulting in mild hypoxemia. In the hypoxemic type, however, the main alteration is the increased D(A-a)O2 caused by the pulmonary parenchyma disease and ventilation/perfusion (V/Q) mismatch.
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