Our data suggest that pulmonary arterial thermodilution and PiCCO may be interchangeably used for cardiac output measurement even under acute haemodynamic changes. The method described by Bland and Altman demonstrated an overestimation of cardiac output for both thermodilution methods. HemoSonic and NICO offer non-invasive alternatives and complementary monitoring tools in numerous clinical situations. Trend monitoring and haemodynamic optimizing can be applied sufficiently, when absolute measures are judged critically in a clinical context. The use of the NICO system seems to be limited during acute circulatory changes.

SummaryWe developed a closed-loop system to control the depth of anaesthesia and neuromuscular blockade using the bispectral index and the electromyogram simultaneously and evaluated the clinical performance of this combined system for general anaesthesia. Twenty-two adult patients were included in this study. Anaesthesia was induced by a continuous infusion of remifentanil at 0.4 lg.kg )1 .min )1 (induction dose) and then 0.25 lg.kg )1 .min )1 (maintenance dose) and propofol at 2 mg.kg )1 3 min later. The combined automatic control was started 2 min after tracheal intubation. The depth of anaesthesia was recorded using bispectral index monitoring using a target value of 40. The target value of neuromuscular blockade, using mivacurium, was a T1 ⁄ T1 0 twitch height of 10%. The precision of the system was calculated using internationally defined performance parameters. Twenty patients were included in the data analysis. The mean (SD) duration of simultaneous control was 129 (69) min. No human intervention was necessary during the computer-controlled administration of propofol and mivacurium. All patients assessed the quality of anaesthesia as 'good' to 'very good'; there were no episodes of awareness. The mean (SD) median performance error, median absolute performance error and wobble for the control of depth of anaesthesia and for neuromuscular blockade were )0

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The control system, reflecting the level of analgesia during general anesthesia designed and evaluated in this study, allows for a clinically practical, nearly fully automated infusion of an opioid during medium-length surgical procedures with acceptable technical requirements and an adequate precision.

The main goals of general anaesthesia should include (not exclusively) adequate hypnosis, analgesia and maintenance of vital functions. In addition, neuromuscular blockade (NMB) may be needed for a number of surgical procedures. Patient safety and cost reductions via the minimization of drug consumption and the shortening of post-operative recovery represent some of the main issues and motivations of automation of anaesthesia.Since the early eighties engineers and physicians joined efforts towards the development of sophisticated closed-loop control systems for drug delivery in the operating theatre and post-operatively.First, this paper should be seen as a review about the automatic drug delivery in anaesthesia. A summary is given about the methods of measurement, modelling and general progress of closed-loop control systems in anaesthesia. In particular, the development of the 'Rostock assistant system for anaesthesia control (RAN)' is also described. This system has been developed during the last 15 years at the University of Rostock and various systems and control-based ideas have been integrated since. With this system the multiple-input-multiple-output (MIMO) control of the depth of hypnosis and NMB has been shown to be possible as well as the closed-loop control of a deep arterial hypotension. Promising results have already been obtained from a first study, which has so far included as many as 22 patients using MIMO control.