The MIRUS™ system enables automated end-expired control of volatile anaesthetics. The device is positioned between the Y-piece of the breathing system and the patient's airway. The system has been tested in vitro and to provide sedation in the ICU with end-expired concentrations up to 0.5 MAC. We describe its performance in a clinical setting with concentrations up to 1.0 MAC. In 63 ASA II-III patients undergoing elective hip or knee replacement surgery, the MIRUS™ was set to keep the end-expired desflurane, sevoflurane, or isoflurane concentration at 1 MAC while ventilating the patient with the PB-840 ICU ventilator. After 1 h, the ventilation mode was switched from controlled to support mode. Time to 0.5 and 1 MAC, agent usage, and emergence times, work of breathing, and feasibility were assessed. In 60 out of 63 patients 1.0 MAC could be reached and remained constant during surgery. Gas consumption was as follows: desflurane (41.7 ± 7.9 ml h), sevoflurane (24.3 ± 4.8 ml h) and isoflurane (11.2 ± 3.3 ml h). Extubation was faster after desflurane use (min:sec): desflurane 5:27 ± 1:59; sevoflurane 6:19 ± 2:56; and isoflurane 9:31 ± 6:04. The support mode was well tolerated. The MIRUS™ system reliable delivers 1.0 MAC of the modern inhaled agents, both during mechanical ventilation and spontaneous (assisted) breathing. Agent usage is highest with desflurane (highest MAC) but results in the fastest emergence. Trial registry number: Clinical Trials Registry, ref.: NCT0234509.

No abstract

To identify the better volatile anaesthetic delivery system in an intensive care setting, we compared the circle breathing system and two models of reflection systems (AnaConDa™ with a dead space of 100 ml (ACD-100) or 50 ml (ACD-50)). These systems were analysed for the parameters like wash-in, consumption, and wash-out of isoflurane and sevoflurane utilising a test lung model. The test lung was connected to a respirator (circle breathing system: Aisys CS™; ACD-100/50: Puriton Bennett 840). Set parameters were volume-controlled mode, tidal volume-500 ml, respiratory rate-10/min, inspiration time-2 sec, PEEP-5 mbar, and oxygen-21%. Wash-in, consumption, and wash-out were investigated at fresh gas flows of 0.5, 1.0, 2.5, and 5.0 l/min. Anaesthetic target concentrations were 0.5, 1.0, 1.5, 2.0, and 2.5%.  Wash-in was slower in ACD-100/-50 compared to the circle breathing system, except for fresh gas flows of 0.5 and 1.0 l/min. The consumption of isoflurane and sevoflurane in ACD-100 and ACD-50 corresponded to the fresh gas flow of 0.5-1.0 l/min in the circle breathing system. Consumption with ACD-50 was higher in comparison to ACD-100, especially at gas concentrations > 1.5%. Wash-out was quicker in ACD-100/-50 than in the circle breathing system at a fresh gas flow of 0.5 l/min, however, it was longer at all the other flow rates. Wash-out was comparable in ACD-100 and ACD-50. Wash-in and wash-out were generally quicker with the circle breathing system than in ACD-100/-50. However, consumption at 0.5 minimum alveolar concentration was comparable at flows of 0.5 and 1.0 l/min.