**Question:** Maintenance level of Mixed Venous Oxygen Saturation in shock must be

A. 70%
B. 80%
C. 74%
D. 90%

**Core Concept:**

Mixed venous oxygen saturation (SvO2) is a measure of the amount of oxygen in the blood returning to the heart from the body's tissues. In shock, there is impaired cardiovascular function leading to inadequate blood flow and oxygen delivery to tissues. Maintaining a sufficient level of SvO2 helps ensure that oxygen is delivered to the tissues and supports adequate organ function.

**Why the Correct Answer is Right:**

The correct answer is **C. 74%**. SvO2 is typically maintained between 70% and 76% in a stable patient. In the context of shock, the maintenance level of SvO2 should be slightly higher to compensate for the decreased tissue perfusion and ensure adequate oxygen delivery to tissues.

**Why Each Wrong Option is Incorrect:**

A. 70% (too low) - Maintaining a lower SvO2 can lead to tissue hypoxia and exacerbate shock's adverse effects.
B. 80% (too high) - A higher SvO2 than necessary can indicate impaired tissue perfusion and is not ideal.
D. 90% (too high) - Similar to option B, maintaining a higher SvO2 than necessary can indicate impaired tissue perfusion and is not ideal.

**Clinical Pearl:**

In shock, maintaining a SvO2 between 74% and 76% allows for an appropriate balance between ensuring adequate tissue oxygenation and avoiding potential complications due to excess oxygen delivery. Close monitoring of SvO2 is essential in managing shock to ensure optimal oxygen delivery to tissues and maintain organ function.