In medicine, for minor procedures such as blood tests or ECG, there is the notion of implied consent. Just holding out your arm for the blood test is implied consent. To refuse, you might say, I am of sound mind and I do not consent to this procedure. Or, you are performing this procedure without my consent and against my wishes. I'm not a lawyer,and not in the US, but this is how it generally operates for practical reasons. Written informed consent is required for more invasive or significant procedures.