(p. 202) Inhalational anaesthetic agents in critical illness 

Inhalational anaesthetic agents have limited applications in the intensive care unit (ICU), as their delivery requires specific equipment, which are not routinely available. Sevoflurane and isoflurane are the two agents eligible for this purpose. They both show good clinical tolerance and versatility, but may raise cerebral blood flow above 1 minimum alveolar concentration. This property makes them unsuitable for sedation in patients suffering from acute brain injury. Sevoflurane is known to be partly metabolized via the cytochrome pathway in inorganic fluoride. This latter accumulates in a dose- and time-dependent manner, especially in a closed circuit with soda lime. However, no clinical renal injury has been proven, despite several studies reporting on sevoflurane in ICUs. A fresh gas flow above 2 L/min is required to limit inorganic fluoride build-up. Halogenates have been proven to allow efficient sedation in ICU patients for up to several days. They may be considered as therapeutic agents especially in refractory status asthmaticus. Insufficient data exist to recommend halogenates to treat status epilepticus. Nitrous oxide, in 50% oxygen, may serve to allow sedation/analgesia for short and moderately procedures. Xenon, an inert gas that discloses anaesthetic properties with extremely fast onset and recovery, and also has no haemodynamic side effects remains confined to the operating theatre. It requires specific anaesthetic machines and is, at present, too expensive to represent a routine inhalational anaesthetic agent.