ICU sedation poses many problems. The action and side-effects of intravenous drugs in the severely ill patient population of an ICU are difficult to control. The incidence of post-traumatic stress disorder after long-term sedation is high. The recent focus on propofol infusion syndrome entails restrictions in the use of this drug. On the other hand, volatile anaesthetics very selectively suppress consciousness but leave many autonomic functions intact. In the absence of perception and disturbed information processing the number of adverse experiences should be lower, leading to a better psychological outcome. Respiration and intestinal motility are not depressed, facilitating modern therapeutic concepts such as early enteral feeding and augmentation of spontaneous breathing. Awakening after inhalational ICU sedation is quick and predictable, extubation can be planned and organized, and the time during which the patient needs very close observation will be short. Technological advances have greatly simplified the application of inhalational anaesthetics. New anaesthesia ventilators offer ventilatory modes and high flow generation comparable to ICU ventilators. However, they are not yet licensed for stand-alone use. The introduction of a volatile anaesthetic reflection filter for the first time enables the concept of inhalational sedation to be performed with very little effort by many ICUs. This 'anaesthetic conserving device' (AnaConDa) is connected between the patient and a normal ICU ventilator, and it retains 90% of the volatile anaesthetic inside the patient just like a heat and moisture exchanger. In this chapter possible advantages of the new concept and the choice of the inhalational agent are discussed. The technical prerequisites are explained, and the practice and pitfalls of inhalational ICU sedation in general and when using the AnaConDa are described in detail.