ATI TEAS (Test of Essential Academic Skills) Version 7ScienceHard
A patient with a history of chronic obstructive pulmonary disease (COPD) presents with worsening shortness of breath and hypoxemia. The nurse administers supplemental oxygen. Which physiological principle explains why excessive oxygen administration can be detrimental to a patient with COPD?
- AIncreased oxygen causes vasoconstriction in the pulmonary arteries, increasing pulmonary vascular resistance.
- BExcess oxygen increases the affinity of hemoglobin for carbon dioxide, impairing CO2 offloading.
- CSupplemental oxygen directly damages alveolar sacs, reducing their elasticity and gas exchange capacity.
- DHigh oxygen levels suppress the chemoreceptors' hypoxic drive to breathe, leading to hypoventilation.
Show answer & explanationAnswer & explanation
Correct answer: D. High oxygen levels suppress the chemoreceptors' hypoxic drive to breathe, leading to hypoventilation.
In patients with chronic hypercapnia (high CO2) like those with COPD, the body's primary respiratory drive shifts from sensing CO2 levels to sensing oxygen levels (hypoxic drive). Administering high flow oxygen can suppress this hypoxic drive, leading to decreased respiratory rate and depth (hypoventilation), which can further increase CO2 and worsen acidosis.
Why the other options are wrong
- A. While oxygen does cause pulmonary vasoconstriction in healthy individuals, the primary concern in COPD is respiratory drive suppression, not increased pulmonary vascular resistance.
- B. The Bohr effect describes how increased CO2 and acidity decrease hemoglobin's affinity for O2, and the Haldane effect describes how oxygenation of blood decreases hemoglobin's affinity for CO2. Neither explains direct impairment of CO2 offloading due to *excessive* O2 in this context.
- C. While prolonged high concentrations of oxygen can be toxic to lung tissue (oxygen toxicity), this is a separate mechanism from the immediate concern of respiratory drive suppression in COPD.
Hypoxic Drive
A respiratory drive in which the body uses oxygen levels, instead of carbon dioxide levels, to regulate breathing, typically found in individuals with chronic hypercapnia.
- Normally, CO2 levels are the primary stimulus for breathing.
- In COPD, chronic high CO2 blunts chemoreceptor sensitivity to CO2.
- Low O2 then becomes the main signal to breathe; high O2 can remove this signal, leading to hypoventilation.
Memory trick: COPD's CO2 Crushes Control, Oxygen Overtakes.