Refer to "Reporting injuries, diseases and dangerous occurrences in health and social care Guidance for employers" http://www.hse.gov.uk/pubns/hsis1.pdf Clinical decisions If a person is injured as a result of an accident arising directly from the conduct of any operation, examination or other medical treatment being carried out by or under the supervision of a registered medical practitioner (RMP) or dentist, the injury is not reportable (RIDDOR regulation 10(1)). The supervision does not need to be direct for the exemption to apply – it is sufficient that the procedure being carried out was laid down by an RMP. Reportable A patient suffers a major injury as a result of a power failure during an operation (not caused by the conduct of the operation). Not reportable:- During a surgical operation, a surgeon removes the wrong organ. The patient subsequently dies. A patient suffers a seizure following a medical procedure. The nursing assistant was following a procedure laid down by an RMP. A paramedic administers a drug to a patient who subsequently dies as a result of an allergic reaction. This would not be reportable, whether or not the correct procedure was being followed. A patient known to be allergic to penicillin is nevertheless given a penicillin-based drug under the supervision of an RMP and subsequently dies.

I never cease to be 'intrigued' by some 'hypothetical' questions. I haven't trawled the information in the link provided by jay but hopefully the answer is in there somewhere. However, as this appears to be a RIDDOR question, and I am curious as to the reference/relevance to vicarious liability.