What is the legal standard of care for medical malpractice?

In Ryan v. Victoria (City) 1999 CanLII 706 (SCC), [1999] 1 S.C.R. 201 Major J. for the court framed the legal concept of standard of care as follows: Conduct is negligent if it creates an objectively unreasonable risk of harm. To avoid liability, a person must exercise the standard of care that would be expected of an ordinary, reasonable and prudent person in the same circumstances. The measure of what is reasonable depends of the facts of each case, including the likelihood of a known or a foreseeable harm, the gravity of that harm, and the burden or cost which would be incurred to prevent the injury. In addition, one may look to external indicators of reasonable conduct, such as custom, industry practice, and statutory or regulatory standards.