![]() => as the alveolar dead space volume increases, more relatively CO2-free gas mixes in with gases from better perfused units, thus lowering the end-tidal PCO2 The size of this difference is a simple index of the amount of alveolar dead space. In a healthy person breathing room air, the difference between arterial PaCO2 and end-tidal PCO2 is small. Normal PaCO2 = 38.3mmHg +/- 7.5mmHg (95% limits, 2 standard deviation.)ĭifference between arterial PaCO2 and end-tidal PCO2 => Thus by convention, arterial and "ideal" alveolar PCO2 values are taken to be identical. Shunt of 10% will cause an alveolar-arterial PCO2 gradient of about 0.7mmHg. => It is much lower in PCO2 because the CO2-free gas from anatomical dead space dilutes even more. Mixed expired PCO2 is the partial pressure of CO2 in the expired gas during a tidal breath. => It is lower than 'ideal' alveolar PCO2, because the almost CO2-free gas from alveolar dead space dilutes and lower the end-tidal PCO2. => ASSUMED to be representative of alveolar gas ![]() ![]() What is the end tidal CO2? How does it differ from arterial CO2 tension and the mixed expired CO2 tension? What factors influence its value? (1995)Įnd-tidal PCO2 is the partial pressure of CO2 at the end of expiration during tidal breathing. Briefly describe the potential causes of a difference between measured end-tidal and arterial partial pressure of carbon dioxide (03B11) (96B7) ![]()
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