Which type of shunt reversal involves unoxygenated blood being delivered into the systemic circulation?

A right-to-left shunt is characterized by unoxygenated blood being delivered into the systemic circulation. In fetal physiology, this occurs when there is an abnormal connection that allows deoxygenated blood from the right side of the heart to mix with oxygenated blood from the left side, thus entering systemic circulation without being properly oxygenated in the lungs. This type of shunt can lead to significant clinical consequences, such as cyanosis, as the systemic circulation receives a mixture that is lower in oxygen content.

In contrast, other types of shunts, like left-to-right shunts, allow oxygen-rich blood to flow from the left side of the heart into the right side, typically resulting in increased blood flow to the lungs, which does not directly deliver unoxygenated blood to the systemic circulation. Intra-abdominal and intraventricular shunts refer to other pathways that are not directly related to the main shunting patterns affecting systemic oxygenation.