In your last post, you wrote (bolding is mine): "Was two questions enough? Maybe, maybe not. However, the pt refused and SIGNED. Sounds like informed consent to me. Kidney failure? Serious, yes. Ambulance ride necessary? No."
The whole point is that a signature does not imply informed consent, nor does it indicate that the patient was competent to refuse. People can be stoned, drunk, crazy, confused, stroking out, demented, overdosed, hypoglycemic, hypoxic, hyponatremic, encephalopathic, concussed, bleeding into their brain, or any combination of those things and still manage to scribble a signature on a refusal form. Every lawyer and medical-legal consultant knows that, so a signature actually means very little.
In order to prove that their refusal was in fact informed and that they did in fact appear competent, you have to document what happened and what was said and how you assessed the patient and the situation. If your documentation shows that your assessment of their competence was limited to two questions and you were only on scene for 5 minutes - when the person was clearly very sick and you should clearly have had reason to be suspect of their mental competence, and then they end up in the hospital a couple hours later, profoundly hypotensive and with severe uremic encephalopathy, you are pretty much screwed unless your documentation thoroughly outlines a very extensive assessment and attempts to convince the patient to change their mind. Because otherwise, it is going to look an awful lot to anyone looking at the situation that you were negligent in your assessment and in your attempt to get them to accept medical attention. The fact that they signed the form isn't going to help you much.
There is all the difference in the world between taking a refusal from someone who doesn't look sick at all and/or gives you no reason to question their competence, and taking a refusal from someone who is obviously very sick and may not really understand what is going on. Doing the latter without doing everything in your power to accurately assess their mental status and convince them that they really need medical attention is ethically questionable and legally risky, whether you have a signature or not.