BackgroundThe MIRUS™ (TIM, Koblenz, Germany) is an electronical gas delivery system, which offers an automated MAC (minimal alveolar concentration)-driven application of isoflurane, sevoflurane, or desflurane, and can be used for sedation in the intensive care unit. We investigated its consumption of volatile anesthetics at 0.5 MAC (primary endpoint) and the corresponding costs. Secondary endpoints were the technical feasibility to reach and control the MAC automatically, the depth of sedation at 0.5 MAC, and awakening times. Mechanically ventilated and sedated patients after major surgery were enrolled. Upon arrival in the intensive care unit, patients obtained intravenous propofol sedation for at least 1 h to collect ventilation and blood gas parameters, before they were switched to inhalational sedation using MIRUS™ with isoflurane, sevoflurane, or desflurane. After a minimum of 2 h, inhalational sedation was stopped, and awakening times were recorded. A multivariate electroencephalogram and the Richmond Agitation Sedation Scale (RASS) were used to assess the depth of sedation. Vital signs, ventilation parameters, gas consumption, MAC, and expiratory gas concentrations were continuously recorded.ResultsThirty patients obtained inhalational sedation for 18:08 [14:46–21:34] [median 1st–3rd quartiles] hours. The MAC was 0.58 [0.50–0.64], resulting in a Narcotrend Index of 37.1 [30.9–42.4] and a RASS of − 3.0 [− 4.0 to (− 3.0)]. The median gas consumption was significantly lowest for isoflurane ([ml h−1]: isoflurane: 3.97 [3.61–5.70]; sevoflurane: 8.91 [6.32–13.76]; and desflurane: 25.88 [20.38–30.82]; p < 0.001). This corresponds to average costs of 0.39 € h−1 for isoflurane, 2.14 € h−1 for sevoflurane, and 7.54 € h−1 for desflurane. Awakening times (eye opening [min]: isoflurane: 9:48 [4:15–20:18]; sevoflurane: 3:45 [0:30–6:30]; desflurane: 2:00 [1:00–6:30]; p = 0.043) and time to extubation ([min]: isoflurane: 10:10 [8:00–20:30]; sevoflurane: 7:30 [4:37–14:22]; desflurane: 3:00 [3:00–6:00]; p = 0.007) were significantly shortest for desflurane.ConclusionsA target-controlled, MAC-driven automated application of volatile anesthetics is technically feasible and enables an adequate depth of sedation. Gas consumption was highest for desflurane, which is also the most expensive volatile anesthetic. Although awakening times were shortest, the actual time saving of a few minutes might be negligible for most patients in the intensive care unit. Thus, using desflurane seems not rational from an economic perspective.Trial registration Clinical Trials Registry (ref.: NCT03860129). Registered 24 September 2018—Retrospectively registered.

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.

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