Cyanide poisoning and arterial oxygen content

[petitebrownie]

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One of the Uworld questions indicated that cyanide would cause arterial PaO2, SaO2 and CaO2 to remain unchanged but venous oxygen content rises while the arterial-venous oxygen gradient falls. Wouldn't the dissolved oxygen (PaO2) decrease with cyanide poisoning??

 

[mw18]

I believe the PaO2 is unchanged because that's happening at the lung, whereas the Cyanide poisoning is happening at the cellular level in mitochondria blocking complex IV. So this prevents diffusion of O2 from blood to tissue, because it won't use it. This blood not being used results in higher O2 content in the venous side.