If a patient is manually ventilated after a period of apnea, what pattern of end-tidal CO2 is expected?

• A. High at first and persisting for several minutes of ventilation
• B. High at first, followed by a steady decrease
• C. Fluctuation of high to low for several cycles
• D. Low at first, followed by a steady rise

Answer: (D)

The correct answer indicates that when a patient is manually ventilated after a period of apnea, the end-tidal CO2 levels are initially low and then rise steadily. This is due to several physiological processes that occur after a period without breathing.

During apnea, the patient is not inhaling or exhaling, leading to a build-up of carbon dioxide (CO2) in the blood, but the CO2 is not being eliminated. When ventilation resumes, the initial low reading of end-tidal CO2 is primarily due to the fact that the patient has not had any air flow, leading to diluted CO2 levels in the airway. As the ventilation begins, the lungs will start to clear out the accumulated CO2 from the alveoli.

The steady rise in end-tidal CO2 follows as fresh air is introduced and normal gas exchange resumes, allowing for a gradual increase in CO2 elimination through the lungs. This rise will continue as the ventilation persists, reflecting the increasing concentration of CO2 being expelled.

In contrast, the other options describe scenarios that do not accurately represent the expected physiological response following a period of apnea.