What is a physician's obligation to ensure that a patient receives the correct result?

The physician is not obligated to guarantee the result nor is the physician (or nurse) bound to make no mistake. What the patient is entitled to is the exercise by the practitioner of reasonable skill, care and judgment. This is described by Rand J. in Wilson v. Swanson, 1956 CanLII 1 (SCC), [1956] S.C.R. 804 at 812: An error of judgment has long been distinguished from an act of unskilfulness or carelessness or due to lack of knowledge. Although universally-accepted procedures must be observed, they furnish little or no assistance in resolving such a predicament as faced the surgeon here. In such a situation a decision must be made without delay based on limited known and unknown factors; and the honest and intelligent exercise of judgment has long been recognized as satisfying the professional obligation.