Which statement best describes a cause of hypercapnia in diving?

• A. Excess CO2 in the system
• B. Increased oxygen delivery
• C. Reduced CO2 production
• D. Overhydration

Answer: (A)

Hypercapnia means there’s more carbon dioxide in the body than can be eliminated. In diving, it most often comes from excess CO2 in the breathing gas or from not removing CO2 effectively—such as when a closed-circuit rebreather scrubber isn’t working properly or gas flow is inadequate, so you end up rebreathing your own exhaled CO2. That’s why the statement describing excess CO2 in the system is the best match. Increasing oxygen delivery doesn’t by itself cause CO2 buildup, reduced CO2 production would lower CO2 levels, and overhydration isn’t a primary driver of CO2 retention in this context.