This section describes the general law of consent to treatment, capacity with respect to treatment decisions, and substitute decision-making in Ontario.
A. Consent to Treatment
1. The Common Law
The common law has long established that health care practitioners must first obtain the consent of a patient before any treatment is provided. Consent may be obtained in either written or oral form, or may be assumed from a patient’s conduct. A failure to obtain consent from a patient or to disclose relevant information may lead to an action in battery. For example, in the case of Allan v. New Mount Sinai Hospital, the issue before the court was whether the plaintiff had consented to the administration of anaesthesia to her arm by the defendant anaesthetist, Dr. Hellman. Linden J. summarized the then common law of consent, and its application to the facts of that case, as follows:
The administration of an anaesthetic is a surgical operation. To do so would constitute a battery, unless the anaesthetist is able to establish that his patient has consented to it. …. An actual, subjective consent, however, is not always necessary if the doctor reasonably believes that the patient has consented. Thus, if a patient holds up an arm for a vaccination, and the doctor does one, reasonably believing that the patient is consenting to it, the patient cannot complain afterwards that there was no consent: O’Brien v. Cunard S.S. Co., Ltd. (1891), 28 N.E. 266. Silence by a patient, however, is not necessarily a consent. Whether a doctor can reasonably infer that a consent was given by a patient, or whether he cannot infer such consent, and must respect the wishes of the patient, as foolish as they may be, always depends on the circumstances.
While our Courts rightly resist advising the medical profession about how to conduct their practice, our law is clear that the consent of a patient must be obtained before any surgical procedure can be conducted. Without a consent, either written or oral, no surgery may be performed. This is not a mere formality; it is an important individual right to have control over one’s own body, even where medical treatment is involved. It is the patient, not the doctor, who decides whether surgery will be performed, where it will be done, when it will be done and by whom it will be done. Dr. Hellman, when told by Mrs. Allan not to use her left arm, had an obligation to comply with her wishes. If he thought it inadvisable, it was his duty to discuss the matter with her and try to convince her to change her mind. The expert evidence of Dr. Renwick was to the effect that this would be the usual thing to do. Dr. Hellman was not entitled to say that he knew what he was doing, and proceed to inject the needle into Mrs. Allan’s left arm contrary to her express wishes.
To be legally valid, the patient’s consent must also be informed: the consent must be obtained after the nature of the treatment has been explained to the patient and the patient has been advised of the risks involved and about any available alternatives to the proposed treatment. Informed consent requires that the patient be “given the proper time and environment in order to assess the information.”
A patient retains the ability to withdraw consent. Withdrawal of consent has been deemed to be valid when a patient is capable of understanding the nature and consequences of withdrawing consent. A health practitioner who continues to provide treatment after consent has been withdrawn may also be liable for battery.
The guiding principle at common law was, and continues to be, the concept of individual autonomy. Courts of different levels have repeatedly cited this concept, including the Ontario Court of Appeal decision in Malette v Shulman:
The doctrine of informed consent holds that no medical procedure may be undertaken without the patient’s consent, obtained after the patient has been provided with sufficient information to evaluate the risks and benefits of the proposed treatment and other available options. The doctrine presupposes the patient’s capacity to make a subjective treatment decision, based on her understanding of the necessary medical facts provided by the doctor and on her assessment of her own personal circumstances.
In 1980, the cases of Hopp v Lepp and Reibl v Hughes were heard by the Supreme Court of Canada and “had a monumental effect on consent litigation in Canada.” The decision of Hopp v Lepp clarified the standard of informed consent such that: “even if a certain risk is a mere possibility which ordinarily need not be disclosed, yet if its occurrence carries serious consequences, as for example, paralysis or even death, it should be regarded as a material risk requiring disclosure.” Thereafter, even remote risks of death had to be disclosed to patients.
In Reibl v Hughes, the patient had consented to undergo elective surgery, namely an endarterectomy to reduce future risk of stroke, but this consent was not informed. The Supreme Court established that, since the plaintiff had consented, the plaintiff could not sue for assault and battery, but could sue in negligence. The Court reasoned that, in essence, the allegation against the physician was that the consent had been obtained negligently – by not providing the information that was pertinent, including the possibility of stroke arising from the elective surgery. The result of this decision was that the plaintiff was required to prove causation on the negligence standard, which asks “what the average reasonable person in the patient’s position would have done in the circumstances.” The plaintiff, Mr. Reibl, was clear that had he been provided with the appropriate information, he would have foregone the elective surgery until such time as his retirement pension vested a year and a half later.
In the very recent Supreme Court of Canada decision in Cuthbertson v. Rasouli (“Rasouli”), McLachlin, C.J., writing for the majority of the Court reviewed the established common law backdrop in Ontario for consent to treatment:
At common law, medical caregivers must obtain a patient’s consent to the administration of medical treatment: Reibl v. Hughes,  2 S.C.R. 880; Hopp v. Lepp,  2 S.C.R. 192. The physician cannot override the patient’s wishes to be free from treatment, even if he believes that treatment is in the vital interests of the patient. The patient’s consent must be given voluntarily and must be informed, which requires physicians to ensure the patient understands the nature of the procedure, its risks and benefits, and the availability of alternative treatments before making a decision about a course of treatment. The requirement for informed consent is rooted in the concepts of an individual’s right to bodily integrity and respect for patient autonomy: see Fleming v. Reid (1991), 4 O.R. (3d) 74 (C.A.).
The common law of consent to medical treatment works well for patients who have the capacity to decide on consent to treatment, in the sense of being able to understand the nature, purpose, and consequences of the proposed treatment. The patient’s autonomy interest — the right to decide what happens to one’s body and one’s life — has historically been viewed as trumping all other interests, including what physicians may think is in the patient’s best interests.
However, the traditional common law approach to medical treatment is more problematic when a patient is incapable of appreciating the nature, purpose, and consequences of the proposed treatment. As explained in Malette v. Shulman (1990), 72 O.R. (2d) 417 (C.A.), at pp. 423-24, the common law doctrine of informed consent “presupposes the patient’s capacity to make a subjective treatment decision based on her understanding of the necessary medical facts provided by the doctor and on her assessment of her own personal circumstances”. When such capacity is lacking, the patient is not in a position to exercise his autonomy by consenting to or refusing medical treatment.
If a patient is incapable, disputes over consent to treatment at common law are resolved in the courts. The focus shifts from the patient’s autonomy interest, which is compromised or extinguished, to whether receiving treatment is in the best interests of the patient. In emergency situations, where tre