First and foremost, a physician must owe a duty of care to patients before his or her competency in performing that duty can be judged. In U. S. jurisprudence, a person has no affirmative duty to assist injured individuals in the absence of a special relationship with them (such as doctor-patient, attorney-client, guardian-ward, etc.). A doctor dining in a restaurant has no duty to come forward and assist a fellow customer who is suffering a heart attack. If the doctor merely continues with his meal and does nothing to help, the ailing person would not have an action for malpractice against him, not-withstanding their harm. However, once a doctor voluntarily decides to assist others or come to their aid, he or she becomes liable for any injury that results from any negligence during that assistance.
Once the requisite doctor-patient relationship is established, the doctor owes to the patient the duty of care and treatment with that degree of skill, care, and diligence as possessed by or expected of a reasonably competent physician under the same or similar circumstances. The "circumstances" include the area of medicine in which the physician practices, the customary or accepted practices of other physicians in the area (the "locality rule"), the level of equipment and facilities available at the time and in that locality, and the exigent circumstances, if any, surrounding the treatment or medical service rendered. The requisite degree of skill and expertise under the circumstances is established by "expert testimony" from other practicing physicians who share the same or similar skill, training, certification, and experience as the allegedly negligent physician.
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