Improved efficiency of the new Mirus™ system challenged by ventilatory settings-a bench study

Abstract

The Mirus™ system (Technologie Institut Medizin GmbH, Germany) enables target-controlled delivery of volatile anaesthetics with open system ventilators. Its interface, positioned between Y-piece and the patient, injects anaesthetic vapor during inspiration, while adsorbing anaesthetic and resupplying it during the next inspiration. A newly introduced interface (Lisa-44) was evaluated under body temperature pressure saturated and normocapnic conditions using a test lung. Volume-controlled ventilation was applied with a 500 mL tidal volume, 10 bpm respiratory rate, and inspiratory flow (IF) times of 2.5 s and 0.5 s. Isoflurane (sevoflurane) target concentrations were stepwise increased to 1.5 MAC and then decreased. An external gas monitor recorded real-time anaesthetic concentrations. End-tidal concentrations (EC) and area under the curve (AUC) were analyzed for each breath. Accuracy and precision were assessed using Bland-Altman plots. Consumption was calculated and compared to historical controls. Mirus EC measurements correlated well with external gas monitor readings. ECs fluctuated around targets, with higher targets requiring more frequent injections and larger AUCs. Anaesthetic consumption was lower than historical controls and comparable to the Sedaconda ACD. At 0.3–0.5 MAC, hourly isoflurane consumption ranged from 1.0 to 1.7 mL (sevoflurane: 3.8–6.1 mL). However, very short IF times significantly increased consumption, reaching 43 mL sevoflurane at an EC of 2.6 vol%, with prolonged injections extending into the expiration phase. The new system demonstrates high accuracy, precision, and improved efficiency, suggesting reduced anaesthetic consumption in clinical use. However, high concentrations combined with very short IF times substantially increase consumption, indicating potential limitations.