Ending suffering vs. preventing it
Thank you, Marko. I checked out the link you shared, and can see that in many cases it would make sense to use that scale.
What we've been hoping to do is prevent his suffering rather than ending it after it starts, as we've been told by two vets now that sooner would be better than later in our boy's situation. The infection will destroy the bone between the sinus and brain and can result in sudden behavior changes (aggression mostly), confusion, seizures, paralysis and other symptoms.
Already he often has trouble breathing. I can only imagine how it would feel if he were in extreme distress in the middle of the night and we were unable to help him. We are already struggling with enough guilt and grief.