Carbon monoxide, a product of combustion, is a toxic gas that has an extremely high affinity for hemoglobin (much higher than that of oxygen for hemoglobin); consequently, as soon as it dissolves in the liquid part of blood at low partial pressure, it diffuses quickly into red blood cells and binds to hemoglobin. In carbon monoxide (CO) poisoning, even with very low partial pressure of inspired CO, CO rapidly binds to hemoglobin (Hgb), leaving a lower fraction of oxygen binding sites on Hgb available to be occupied by oxygen. What would you expect to find if you measure the arterial PO2 of a person with CO poisoning

The arterial PO2 of a person is decreasing because of carbonmonoxide poisoning due to higher affinity to hemoglobin than oxygen. The PO2 in the blood of arteries are used up by the cells and then there is higher concentration of carbonmonoxide in the blood as compared to oxygen. Due to this higher amount of carbonmonoxide in the blood, many complications occur such as headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion.