Which of the following will alter the position or slope of the CO2-ventilatory response curve EXCEPT?

Which of the following will alter the position or slope of the CO2-ventilatory response curve EXCEPT?

• A. Hypoxemia
• B. Fentanyl
• C. N2O
• D. Ketamine

Answer: (D)

The CO2-ventilatory response curve shows how minute ventilation changes as PaCO2 rises. Its position and slope reflect how strongly the respiratory system responds to CO2. Factors that affect central chemoreceptor sensitivity or peripheral chemoreceptor input can shift this curve or change its steepness. Hypoxemia makes the carotid bodies more responsive to CO2, so for a given PaCO2 ventilation increases more. That moves the curve to show a higher ventilatory response at lower CO2 levels (a leftward/steeper appearance). Fentanyl depresses the brainstem respiratory centers and blunts the CO2 response, reducing sensitivity and shifting the curve to the right with a flatter slope. Nitrous oxide, especially in combination with other anesthetics, can dampen central respiratory drive, producing a rightward shift or decreased slope as well. Ketamine, unlike the others, tends to preserve or even enhance respiratory drive and CO2 responsiveness, so it does not meaningfully alter the curve’s position or slope. Therefore, ketamine is the one that does not alter the CO2-ventilatory response curve.

The CO2-ventilatory response curve shows how minute ventilation changes as PaCO2 rises. Its position and slope reflect how strongly the respiratory system responds to CO2. Factors that affect central chemoreceptor sensitivity or peripheral chemoreceptor input can shift this curve or change its steepness.

Hypoxemia makes the carotid bodies more responsive to CO2, so for a given PaCO2 ventilation increases more. That moves the curve to show a higher ventilatory response at lower CO2 levels (a leftward/steeper appearance). Fentanyl depresses the brainstem respiratory centers and blunts the CO2 response, reducing sensitivity and shifting the curve to the right with a flatter slope. Nitrous oxide, especially in combination with other anesthetics, can dampen central respiratory drive, producing a rightward shift or decreased slope as well. Ketamine, unlike the others, tends to preserve or even enhance respiratory drive and CO2 responsiveness, so it does not meaningfully alter the curve’s position or slope.

Therefore, ketamine is the one that does not alter the CO2-ventilatory response curve.