A characteristic feature of cyanide poisoning is bright red venous blood. This occurs because hemoglobin is unable to release the oxygen during peripheral blood circulation.
Arteriolization of venous blood refers to an elevated hemoglobin saturation, much higher than normal.
Usually oxygen saturation of arterial blood is > 95% while that of venous blood is around 70% reflecting oxygen dissociation in the capillaries.
With cyanide poisoning the oxygen saturation of mixed venous blood may be > 90%.
The differential diagnosis would include a large arteriovenous shunt in the extremity from which the venous blood is drawn.
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