Informed consent to participation in research is an important protector of potential subjects' rights and autonomy. Ethical research involving critically ill people is challenging because their medical condition often makes obtaining informed consent impossible. This is especially true in the prehospital setting, where additional barriers to obtaining informed consent exist. A recently published Canadian policy (Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans) specifies circumstances under which an exception to the requirement for informed consent may be granted so that vulnerable individuals are not denied the potential benefits of participating in research. This article reviews the rationale for the Tri-Council Policy Statement and illustrates some problems with its application in the context of a Canadian prehospital study on continuous positive airway pressure. A new risk analysis model and a national research ethics board are discussed as possible ways to facilitate interpretation and application of the current exception of informed consent policy.