Use of MIRUS™ for MAC-driven application of isoflurane, sevoflurane, and desflurane in postoperative ICU patients: a randomized controlled trial

Abstract

Background: The 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.

Results: Thirty 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.

Conclusions: A 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.

Keywords: Desflurane; Inhalational sedation; Isoflurane; MAC-driven sedation; Sevoflurane.

Fig. 1

Study design. After intravenous induction of anesthesia in the operating room, patients obtained a balanced anesthesia with sufentanil and sevoflurane at 1.0 MAC via a standard anesthetic machine during surgery. At the end of surgery, sedation was switched to an intravenous regime with propofol for the transport from the operating room to the intensive care unit (ICU). After a minimum of 1-h intravenous sedation in the ICU, patients obtained isoflurane, sevoflurane, or desflurane at 0.5 MAC via MIRUS™. As soon as the criteria for a wake-up test were met, a spontaneous breathing trail was performed. Once patients passed the test the MAC was set to 0. The dark blue lines mark the course of the MAC throughout the study

Fig. 2

Awakening times. The time needed to decrease the MAC from 0.5 to 0.25 was longest for ISO (pink box) and quickest for DES (blue box). Correspondingly, awakening was quickest after DES sedation, followed SEVO (yellow box) and ISO. Median (horizontal black lines), 1st and 3rd quantile (upper and lower end of the boxes), the 95% interval (horizontal black lines) and statistical outliers (circles: outside the 95% interval) are presented. *DES is significantly quicker than ISO; ^#SEVO is significantly quicker than ISO