An advance decision allows you to identify which treatments you would like to refuse in certain circumstances, such as a wish to not be resuscitated. It must define the exact medications you would like to decline in situations that have to be clearly set out.
It is good practice to get your advance decision in writing, so that your loved ones and all those involved in your care can have a copy.
Not only should you review it regularly, but you should also know that if you ever need to make any changes to it, this can be done whenever you like. When you have clearly communicated and recorded these changes, ensure that you sign and date it.