Apnea and CO2 rise

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This is for the smarty pants in all of you ... I was asked in clinical last night - "How long would it take the CO2 to rise from 35 to 60 after the patient has become apneic?" Any guesses?

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This is for the smarty pants in all of you ... I was asked in clinical last night - "How long would it take the CO2 to rise from 35 to 60 after the patient has become apneic?" Any guesses?

3mmHg per minute of apnea

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CO2 rises about 7 torr or mmHg in the first minute, then 3 torr each minute thereafter. For a 25 torr increase- approximately 7 minutes (25-7=18/3=6, 1min + 6minutes = 7) assuming normal production of CO2.

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Can someone offer a good explanation as to why the PaCO2 increases much more (~7 mmHg) in the first minute of apnea before leveling off (~3 mmHg)? Thanks.

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