ABCP Perfusion Basic Science (PBSE) Practice Exam

How should DO2 and SvO2 trends be interpreted during CPB?

SvO2 trends do not relate to DO2. DO2 is independent of SvO2. Rising SvO2 always indicates tissue hypoxia. DO2 is sufficient; rising SvO2 suggests adequate delivery or reduced extraction; falling SvO2 suggests inadequate DO2 or high extraction.

Correct Answer:

DO2 is sufficient; rising SvO2 suggests adequate delivery or reduced extraction; falling SvO2 suggests inadequate DO2 or high extraction.

Explanation:

Oxygen delivery must meet tissue oxygen demand on CPB, and SvO2 shows the balance between delivery and consumption. When DO2 is sufficient, tissues don’t extract as much O2 and SvO2 stays normal or increases. A rising SvO2 therefore points to adequate delivery or a reduction in oxygen extraction (for example from cooling or lower metabolic rate). Conversely, SvO2 falling suggests DO2 is inadequate or that tissues are extracting more O2 to meet demand. So interpreting trends this way—DO2 sufficient with SvO2 rising; SvO2 falling with potential DO2 insufficiency or high extraction—is correct. Rising SvO2 does not indicate tissue hypoxia; it typically argues against it.

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