What is the test for determining liability for failure to obtain informed consent in a medical malpractice case?

As Sharpe mentions (at p. 36), the most interesting aspect of Kelly v. Hazlett is the manner in which the finding of liability was developed. Rather than basing liability in battery, liability for failure to obtain the patient s informed consent was based on a failure to disclose risks being a breach of the physician s general duty of care to give reasonable information and advice to the patient. Where the basic nature and character of the operation performed is substantially that which the patient was advised of and agreed to, then there is not an unconsented-to invasion of the person constituting battery, regardless of any failure to disclose collateral risks associated with the operation. An action framed in battery would not succeed. However, such failure, if not justified by reasonable medical considerations, may properly be the basis for a claim in negligence should the procedure result in damage to the patient. In this theory, even where a risk is collateral but still material, if its disclosure is essential to an informed decision to undergo the operation, lack of such disclosure should vitiate the consent.