Automated Control of End-tidal Volatile Anesthetic Concentration

Overview

The new MIRUS system as well as the established AnaConDa system uses a reflector to conserve volatile anaesthetics (VA). Both systems act with commercially available ICU ventilators. In contrast to AnaConDa the MIRUS includes an automated control of end-tidal VA concentrations. In this study the investigators compared feasibility, costs and recovery times after anaesthesia with isoflurane (ISO), sevoflurane (SEVO) or desflurane (DES) in ventilated and spontaneously breathing patients.

The study was approved by the appropriate Institutional Review Board. After written informed consent 63 ASA I-III patients undergoing elective hip or knee replacement surgery under general anesthesia were included. Patients were randomly organized into 3 groups (20-22 each). Anesthesia was induced with intravenous anaesthetics. After tracheal intubation MIRUS automatically adjusted the end-tidal VA concentration to 1.0 MAC. Patients were ventilated with the Puritan Bennett 840 ICU ventilator. After 1 h of anaesthesia with 1.0 MAC the ventilator mode was switched from SIMV V+ (totally controlled ventilation, "passive patient", with a tidal volume of 8 ml/IBW) to proportional assist ventilation (PAV) with 50% support ("active patient"). At the end of surgery the MIRUS system was stopped (MAC set to 0.0) and recovery times were measured.

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