Total Intravenous Anaesthesia with an Integrated Computer Control System

Copyright © IFAC Modelling and Control in Biomedical Systems, Warwick, UK, 1997

TOTAL INTRAVENOUS ANAESTHESIA WITH AN INTEGRATED COMPUTER CONTROL SYSTEM ·PE astwood, • D.A. Linkens . •• N.D. Edwardsi#,J.J. Ross# • C.S. Reilly • # DGM . . uson,.

"Intelligent Systems Laboratory, Department ofAutomatic Control & Systems Engineering, # University Department ofSurgical & Anaesthetic Sciences, Northern General Hospital, University ofSheffield, South Yorkshire, United Kingdom Facsimile: +44-(0)114 273 1729, E-mail: [email protected]

Abstract: An integrated multivariable computer control system is currently under development to assist anaesthetists in the administration of anaesthetic, analgesic and muscle rela"{ant infusions for total intravenous anaesthesia This multivariable system is the integration of several single variable systems developed by the research team. A serial multiplexer was developed by the research team to allow communication of multiple infusion and monitoring devices via a single computer serial port. Initially the system was arranged with phannacokinetic model-driven systems for the anaesthetic and analgesic agents and a Relaxograph (Datex) monitor was used for fuzzy closed-loop control of neuromuscular block (NMB) .

Keywords : System integration, Computer Control, Biomedical Systems. Biomedical Control, Closed-loop Control.

1. INTRODUCTION

anaesthesia ([avernier, et al., 1987). In contrast, our research effort is aimed towards feedback control in this domain.

The use of computers for automation in anaesthesia is recorded in the literature more than forty years ago (Soltero. et al., 1954). Since then computers are now equipped \\ith much greater computational power and can even sit on your palm. In addition anaesthetics has moved away from inhalational towards intravenous agents which are administered via infusion pumps. There can now be three separate anaesthetic infusions for control of patient awareness, analgesia and muscle relaxation. We could therefore use three separate computers to control each of these infusions. However, to assist in the development of an integrated multivariable control strategy, we have developed a serial multiplexer which allows the computer to communicate with multiple monitoring and infusion devices via a single serial port. A similar system has been reported in the literature by a Belgian research group aimed at using model-driven infusions for

It is difficult to obtain relevant, reliable on-line patient measurements in anaesthesia for feedback control. Monitoring of neuromuscular block is more reliable than those currently available for monitoring patient awareness or sensed pain (plourde, 1991 ; Newton, 1993). However, even this measurement is subject to measurement drift and inaccuracy due to changes in electrode impedance as conductive jelly dries up. In addition, patient temperature alters through a surgical procedure \....hich changes properties of the neuromuscular junction. This measurement problem has often led to the use of open-loop model-based control schemes relying heavily on clinical feedback via the supervising anaesthetist for adjustment of system setpoints (Schuttler, et al., 1988). Our aim is to utilise a combination of available on-line patient

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measurements to develop closed-loop control schemes which provide improved quality of anaesthesia and reduce the clinical workload (Klein and Davis, 1981; Schwilden, et al., 1989; Chilcoat et al., 1984). The supervising anaesthetist still serves an essential but less demanding role in interpreting clinical feedback and altering setpoints as deemed appropriate (Baer, 1991). 2. METIIODS Our serial multiplexer was designed around the Intel 80C188EB embedded processor running at a CPU clock speed of 12MHz. The two built-in serial channels of the embedded processor are utilised. A further four serial channels were made available by interfacing a PLCC-packaged Philips SC26C94 Quad UART device to the processor. Vectored interrupts are used for all si..... serial communication channels and serial data is software-buffered in 32Kb RAM both on receive and transmit operations. One channel is dedicated to communication with the computer leaving five channels for communication with other serial devices. A serially programmed 32Kb EEPROM holds system software and configuration parameters (e.g. baud rate, parity) for

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each channel. The PCB is small, measuring 150 mm by 100 mm and has minimal power requirements with battery back-up. Our initial set of equipment attached to the control system comprised a Relaxograph (Datex) for NMB monitoring, Aspect-lOO EEG bispectral index for monitoring patient awareness (Kearse, et al., 1994) and three Graseby Medical 3400 infusion pumps infusing atracurium (muscle rela'Xant), propofol (anaesthetic) and alfentanil (analgesic) (Figure 1). The Relaxograph provides feedback for closed-loop fuzzy control of the muscle rela"'
Anaesthetist

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t--~~ ~--;

Reloxograph NMB monitor

Muscle Relaxant Infusion Pump

Patient ~_-;

Serial Computer ~--I Multiplexer IE---;

Anaesthetic Infusion Pump

AnalgesiC Infusion Pump

Aspect EEG monitor

Fig. 1. An information flow diagram of the integrated computer control system which utilises a custom-designed serial multiplexer to interface multiple monitoring and infusion devices to a single computer via a single serial port.

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Schuttler, 1., S. Kloos, H. Sch\vilden and H. Stoeckel (1988). Total intravenous anaesthesia with propafol and alfentanil by computer-assisted infusion. Anaesthesia 43 (suppl), 2 - 7. Schwilden, H., H. Stoeckel and 1. Schuttler (1989). Closed-loop feedback control of propafol anaesthesia by quantitative EEG analysis in humans. Br J Anaesth 62, 290 - 296. Soltero, D., A. Faulconer and R Bickford (1954). The clinical application of automatic anesthesia. Anesthesiology 12, 574 - 582. Tavernier, A., E. Coussaert and F. Cantraine (1987). Model-based pharmacokinetic regulation in computer-assisted anesthesia using an interactive system: CARIN. Acta Anaesth Be/gica 38, 63 - 68

3. DISCUSSION

It would be desirable to add further serial channels to the multiplexer for on-line collection of more measurements such as blood pressure and heart rate. It is possible to interface another quad UART to the embedded processor. Alternatively, a second serial multiplexer could easily be connected to the second serial pon on the computer. Otherwise, we could cascade them while still only using one serial pon although thereby incurring propogation delays. TIlls integrated computer control system will provide us \vith necessary synchronised patient data for developing an integrated multivariable computer control system for use in anaesthesia. REFERENCES Baer, T. (1991). The supervisory system takes control. }vfanaging Automation 6, 40-43 . Chilcoat, R T., J.N. Lunn and W.W. Mapleson (1984). Computer assistance in the control of depth of anaesthesia. Br J Anaesth 56, 1417 1431. Kearse, L.A., P. Manberg, N. Chamoun, F. deBros and A. Zaslavsky (1994). Bispectral analysis of the EEG correlates \\ith patient movement to skin incision during propofol/nitrous oxide anesthesia. Anesthesiology 81, 1365-1370. Klein, F.F. and D.A. Da.is (1981). The use of time domain analyzed EEG in conjunction \\ith cardio\'ascular parameters for monitoring anesthetic levels. IEEE Trans BA,I E 28, 3640. Mason, D.G .. D.A. Linkens. N.D. Edwards and C.S. Reilly (1994). Automated delivery of muscle rela-..ants using fuzzy-logic control. IEEE Engineering in }vfedicine & Biology 13, 678686. Mason. D.G .. N.D. Edwards, D.A. Linkens and C.S. Reilly (1996a). Performance assessment of a fuzzy controller for atracurium-induced neuromuscular block. Br J Anaesth 76, 396400. Mason, D.G .. C.F. Swinhoe, D.A. Linkens and C.S. Reill\' CS (1996b). Development of a pharmacokinetic model-driven system for ketarnine analgesia. Int J Clinical J'vfonitoring & Computing 13, 139-142 Mason, D.G., D.A. Linkens, N.D . Edwards and C.S. ReiIly CS (1997). Development of a ponable closed-loop atracurium infusion system: Systems methodology and safety issues. 1nt J Clinical Afonitoring & Computing Newton, D.E. (1993). Depth of anesthesia. Anaesthesia 48. 367 - 368. Plourde. G. (1991). Depth of anaesthesia, Canadian J Anaesthesia 38, 270 - 274.

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