Answer and Explanation 22

22.  B is the correct answer.  The pulmonary artery is the last place the blood goes before it is reoxygenated and thus the most accurate place to obtain a mixed venous blood gas.  The pulmonary vein and aorta have oxygenated blood already and the femoral vein will give a sample but it will tend to reflect the local metabolic activity but still can be helpful clinically.