This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Maintenence level of Mixed venous oxygen saturation in shock must be 
Select and explain. 
A. >70%, B. 50-70%, C. 40-50%, D. <40%
B: 50-70%
Answer: B: 50-70% 
Explanation: Mixed venous oxygen saturation The percentage saturation of oxygen returning to the hea from the body is a measure of the oxygen delivery and extraction by the tissues. Accurate measurements is analysis of blood drawn from a long central line placed in the right atrium Normal mixed venous oxygen saturation levels are 50-70%. Levels below 50% indicate inadequate oxygen delivery and increased oxygen extraction by the cells. This is consistent with hypovolemic or cardiogenic shock. Ref: Bailey and love 27th edition Pgno: 17