The best strategy by far for avoiding having JWs finding you via the hospital records is to NEVER EVER TELL THEM that you are / were a JW. When they ask if you belong to a religion, JUST SAY NO.
I've encountered JW Elders™ at the hospital where I work. They are provided with a special "Pastoral Care" badge that authorizes them to be in the hospital, LOOKING UP ALL THE JW PATIENTS ostensibly to provide "pastoral visits". While they don't have access to your chart, they can just show up at your bedside and observe the surroundings - even if you are sound asleep or unconscious. If you've consented to a blood transfusion, and are unconscious / asleep when they show up and they see blood hanging and infusing into you, you are automatically Disassociated By Your Actions™.
Don't give them the satisfaction. They will get a print-out from pastoral services listing all JW patients. If you aren't on their list, they can't find you.