No, medical malpractice cases cannot be reopened once they’ve been settled. Once a settlement is reached, both parties sign a release in which they forfeit the right to take any legal action in the future in relation to the incident.
In fact, this is true for any type of civil case. You get one shot–no matter the circumstances. That’s why it’s crucial that you secure trustworthy counsel (especially in such cases of medical malpractice), and that you fully understand the extent of your losses.