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

What finding is characteristic of high mVO2 in distributive shock?

1. Increased cardiac output

2. Increased systemic vascular resistance

3. Low pulmonary capillary wedge pressure

4. Normal acid secretion

The correct answer is: Increased cardiac output

In distributive shock, which includes conditions such as septic shock, there is a profound alteration in the body's hemodynamics. A characteristic finding in this type of shock is increased cardiac output despite the presence of low systemic vascular resistance due to widespread vasodilation. High mixed venous oxygen saturation (mVO2) indicates that there is an elevated delivery of oxygen to tissues, which often occurs because the body compensates for the decreased effectiveness of blood flow through peripheral tissues—leading to increased cardiac output. The heart works harder and pumps more blood in an attempt to maintain adequate oxygen delivery to the tissues amidst a low systemic vascular resistance state. In terms of the other options, an increase in systemic vascular resistance would typically indicate improved perfusion pressures and is not characteristic of distributive shock, where resistance is low. Low pulmonary capillary wedge pressure often reflects the loss of preload due to vasodilation and fluid shifts, not necessarily indicating high mVO2. Normal acid secretion does not relate directly to the hemodynamic changes seen in distributive shock and mixed venous oxygen saturation levels. Thus, increased cardiac output is the hallmark finding associated with high mVO2 in the context of distributive shock, showcasing the body's compensatory mechanisms in response to reduced