Why does pulmonary embolism give normal C02 level?

[scilearner]

Hello everyone,

This has bothered me for sometime now.

Ok Pulmonary embolism , now decreased perfusion into a part of lung. No blood available for oxygen from lung to diffuse into. Blood has decreased oxygen. That is fine but since no blood is reaching the lungs, the carbon dioxide should also be retained in blood, shouldn't this elevate carbon dioxide in blood. Ok I understand body now goes into relfex tachypnoea to get more oxygen in mean time, and this will also push carbon dioxide out. But how can this reduce carbon dioxide level, if the lung is not receiving carbon dioxide from blood anyway, due to decrease perfusion. Thanks

[Prometheus]

Generally hypoxia kills much faster then type II respiratory failure, so maybe in the long term we would see CO2 retention but death or medical intervention prevent it from happening.

 

Another speculation could be that the dissociation curves for the two gases are different such to allow adequate CO2 exchange but insufficient O2 exchange (as an initial check you could look at the dissociation curves to see if this is theoretically possible).