A client's values contain 3 normal PO2 values. The values are 40mmHg, 100mmHg and 160mmHg. Which sample is (a) arterial blood?____________ (b)venous blood?____________ and (c) inspired air?_______________. From your answer, predict the PO2 in the alveoli.
We are looking at pO2 values of 40, 100, and 160 mmHg. These are values of the partial pressure of oxygen either in the air or dissolved in blood. The standard atmospheric air pressure is 760 mmHg, and oxygen makes up ~21% of the atmospheric gasses. That means that 760 * 0.21 = 160 mmHg is the partial pressure of oxygen in the air. So the 160 mmHg value is for (c), the inspired air (air inhaled into the lungs).
The other two choices are arterial blood and venous blood. Since arterial blood has come directly from the lungs with fresh oxygen and venous blood has already been traveling around the entire body, we know that more oxygen will be contained in the arterial blood than the venous blood. That means 100 mmHg is the value for (a) and 40 mmHg is the value for (b).
Based on these numbers, one can predict that the pO2 in the alveoli will be close to that of arterial blood. The lining of the alveoli is where gas diffusion of O2 and CO2 between the lungs and arterial blood takes place. So the pO2 in the alveoli should be around 100 mmHg.