It’s a reference to the TNG episode Chain of Command

My Lemmy client can’t do spoiler tags, but the explanation for the “four lights” part is in the plot section of the linked wiki article

If it is anything like other surgeries done at vets, the risky part with such an old animal is the sedation, not the surgery itself. And with animals you usually need to fully sedate them, as they don’t understand that they need to stay still.