 The combination of remifentanil and propofol infusions is a widely used method of total intravenous anaesthesia. 1 Target controlled infusion TCI is a pharmacokinetic PK infusion system using data from a large population of patients to calculate and deliver stable concentrations of a drug based on a three compartment PK model. Both propofol and remifentanil are ideal drugs for delivery in this way because of their quick distribution, metabolism and excretion. 2 Remifentanil is a potent synthetic opioid receptor MOR agonist with a short recovery irrespective of the duration of its administration. This is due to it being quickly broken down by non-specific esterases in blood and tissues. 3 Remifentanil like all opioids is not very hypnotic in clinically relevant concentrations. 4 