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Old 02-05-2012
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Lungs Ventilation relation to PCO2

A hysterical patient is hyperventilating and doubles his Alveolar ventilation. If his initial PA Co2 was 40 mmHg, and his CO2 production stays unchanged. what will be his PA Co2 on Hyperventilation?

A) 80
B) 60
C) 20
D) 10
E) 4
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cos alveolar ventilation doubled== CO2 level halved

PaCo2--- will be halved... ie 20

PACO2 level will be doubled ie 80
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C seems correct
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PACo2 = V co2 / V A

Answer is 20 mmHg
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Quote:
Originally Posted by dr_ace_img View Post
PACo2 = V co2 / V A

Answer is 20 mmHg
can u pls explain.. im lost
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The Partial pressure of Alveolar Co2 equals the Ventilation of the Co2 by the Alveolar Ventilation.

Therefore, when we increase Alveolar ventilation (in this case hyperventilation) we cut the PA co2 by half.

Well to put it in different perspective: When the Denominator goes up (in this case Alveolar Ventilation), the PA Co2 goes down...just a simple math...you just need to know the formula!

PA Co2 = (V Co2) / (VA)

Did this help?
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