Hemoglobin (hb) and oxygen gas form a complex (hbo2) that carries oxygen throughout the human body. unfortunately, carbon monoxide also binds to hemoglobin so that equilibrium is established. carbon monoxide poisoning occurs when the concentration of hbo2 in the blood is reduced.

The equation of the equilibrium should look like this:
HbO2 + CO--> HbCO + O2

Poisoning occurs when the concentration of hbo2 in the blood is reduced because CO will cause the reaction move to the right.
Remove the victim to an area of fresh air will stop the CO gas that diffuses into the blood from the lungs. Since the supply of the CO stopped, the reaction to the right will move slower.
Administering (a high pressure) oxygen will cause the reaction shift to the left because there are more O2 than CO. The oxygen will unbind the CO from haemoglobin, so it could be released in the lungs.