American Board of Surgery Qualifying Exam (ABS QE) Practice Test

Which type of shock typically presents with low mixed venous oxygen saturation (mVO2)?

1. Hypovolemic shock

2. Cardiogenic shock

3. Distributive shock

4. Septic shock

The correct answer is: Hypovolemic shock

The type of shock that typically presents with low mixed venous oxygen saturation (mVO2) is associated with hypovolemic shock. In hypovolemic shock, there is a significant reduction in intravascular volume, which leads to inadequate tissue perfusion and oxygen delivery. As the body attempts to maintain vital organ function, oxygen extraction by the tissues increases due to decreased delivery. This results in a lower than normal mVO2 because the tissues are not receiving sufficient blood flow or oxygen to meet their metabolic demands, leading to increased extraction of oxygen from the limited volume of circulating blood. In contrast, in cardiogenic shock, the heart's ability to pump efficiently is compromised, which can lead to various abnormalities in oxygen delivery and extraction, but the mVO2 may not be low because the issue arises from inadequacy in the pump rather than a lack of volume. Distributive shock, such as in septic shock, often has adequate cardiac output but suffers from significant peripheral vasodilation, leading to heterogeneous blood flow and potentially normal or elevated mVO2 despite the presence of shock. In septic shock specifically, the dysfunction in oxygen utilization can create a different profile in mVO2 that may not be indicative of low levels as seen in hyp