The issue in a medical negligence action is whether the defendant deviated from approved or appropriate practice. It is an error, usually, to think that the plaintiff will succeed if he/she proves that there would have been no injury had the defendant followed a different course of action. (The exceptional case where it would not be an error would be one where the court was persuaded that the conventional practice carried such obvious defects that it was indefensible and where the court effectively condemns the defendant and the practice.)
A plaintiff must prove the liability of the defendant. This is not equivalent to proving causation. Liability may arise where proof of an error in judgment or management is established, but the plaintiff must go in to prove that that error was the cause, or a cause, of the untoward outcome for the patient.