Which condition is least likely to lower mixed venous oxygen saturation (SVO2)?

Mixed venous oxygen saturation (SVO2) represents the amount of oxygen remaining in the blood after it has circulated through the body and delivered oxygen to tissues. Several conditions can affect SVO2, generally either by increasing oxygen consumption or decreasing oxygen delivery.

In the case of cyanide poisoning, it primarily affects the ability of cells to utilize oxygen. Cyanide inhibits the enzyme cytochrome c oxidase in the mitochondrial electron transport chain, preventing cells from using oxygen effectively for metabolism. This means that even though oxygen may be present and potentially saturating hemoglobin, cells cannot utilize it, leading to a situation where the blood returning to the lungs may still have a high oxygen content. As a result, SVO2 can remain normal or even elevated in cases of cyanide poisoning due to this inability to use the available oxygen, making it less likely for this condition to lower SVO2.

In contrast, anemia, hypoxemia, and shivering can lower SVO2 levels. Anemia decreases the oxygen-carrying capacity of the blood, leading to lower delivery of oxygen to tissues and therefore potentially lower SVO2. Hypoxemia, or reduced oxygen levels in the blood due to various reasons such as lung disease or altitude, also