New technical developments for inhaled sedation

Abstract

The circle system has been in use for more than 100 years, whereas the first clinical application of an anaesthetic reflector was reported just 15 years ago. In thecircle system, all breathing gas is rebreathed after carbon dioxide absorption. Areflector, on the other hand, with the breathing gas flowing to and fro, specifically retains the anaesthetic during expiration and resupplies it during the next inspiration. Ahigh reflection efficiency (number of molecules resupplied/number of molecules exhaled, RE 80-90%) decreases consumption. In analogy to the fresh gas flow of acircle system, pulmonary clearance ((1-RE)× minute ventilation) defines the opposition between consumption and control of the concentration.It was not until reflection systems became available that volatile anaesthetics were used routinely in some intensive care units. Their advantages, such as easy handling, and better ventilatory capabilities of intensive care versus anaesthesia ventilators, were basic preconditions for this. Apart from AnaConDa™ (Sedana Medical, Uppsala, Sweden), the new MIRUS™ system (Pall Medical, Dreieich, Germany) represents asecond, more sophisticated commercially available system.Organ protective effects, excellent control of sedation, and dose-dependent deep sedation while preserving spontaneous breathing with hardly any accumulation or induction of tolerance, make volatile anaesthetics an interesting alternative, especially for patients needing deep sedation or when intravenous drugs are no longer efficacious.But obviously, the outcome is most important. We know that deep intravenous sedation increases mortality, whereas inhalational sedation could prove beneficial. We now need prospective clinical trials examining mortality, but also the psychological outcome of those most critically ill patients sedated by inhalation or intravenously.