Physiologic parameters during a choking episode! - USMLE Forums
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Old 08-01-2011
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Lungs Physiologic parameters during a choking episode!

A man has been hospitalized for 2 weeks for exacerbation of multiple sclerosis. While dining one evening in his bed, he chokes on a piece of food and the nurse is alerted. The Heimlich maneuver is performed and it is found that a large piece of steak was caught in this man's trachea. Which of the following is most accurate about the man during the choking incident?
A. PaO2 = 40; PaCO2 = 45
B. PaO2 = 100; PaCO2 = 40
C. PaO2 = 150; PaCO2 = 0
D. V/Q → infinity
E. Physiological dead space was increased
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Old 08-01-2011
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Old 08-01-2011
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A....? but how come PaCo2 have not risen more than 45 mm hg?
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Old 08-02-2011
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A. PaO2 = 40; PaCO2 = 45
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Correct Answer answer

The correct answer is A.
Complete obstruction of the airway leads to the creation of an intrapulmonary shunt. In this case, the lungs are not being ventilated, but they are still being perfused. Thus V/Q → 0.

If the lungs are not being ventilated, the arterial pressures of O2 and CO2 will approach that of mixed venous blood. This occurs because gas from venous blood can not be exchanged in the pulmonary vasculature.

PaO2 = 100; PaCO2 = 40 - these are the normal values for O2 and CO2.

PaO2 = 150; PaCO2 = 0 - arterial oxygen does not approach values above 100. This is more consistent with the alveolar pressures generated in dead space
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