Cardiopulmonary bypass (CPB) is the keystone of most of these surgeries, as it allows for the maintenance of patient circulation without the requirement for a beating heart or breathing lungs. However, in doing so, CPB creates a unique set of difficulties associated with administering and maintaining anaesthesia. Firstly, the usual route of administration of inhalational anaesthetics, such as isoflurane, via the lungs is impossible. Secondly, clinical signs used to assess depth of anaesthesia, such as heart rate and systemic arterial blood pressure, are obscured by the mechanical support of the circulation. As a consequence, maintaining and assessing the depth of anaesthesia achieved during CBP provides challenges for the anaesthetists.