On Automation in Anesthesia

137 Pages·2013·5.93 MB·English

by  Kristian Soltész

On Automation in Anesthesia
Soltesz, Kristian
2013
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Citation for published version (APA):
Soltesz, K. (2013). On Automation in Anesthesia. [Doctoral Thesis (monograph), Department of Automatic
Control]. Department of Automatic Control, Lund Institute of Technology, Lund University.
Total number of authors:
1
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LUND UNIVERSITY
PO Box 117
221 00 Lund
[phone]
On Automation in Anesthesia
Kristian Soltész
DepartmentofAutomaticControl
Department of Automatic Control
Lund University
PO Box 118
SE-221 00 Lund
Sweden
PhD Thesis
ISRN LUTFD2/TFRT--1096--SE
ISSN 0280–5316
ISBN 978-91-7473-484-3
(cid:13)c 2013 by Kristian Soltész. All rights reserved.
Printed in Sweden by Media-Tryck.
Lund 2013
SzeretettNagytatámnak

Abstract
The thesis discusses closed-loop control of the hypnotic and the analgesic
components of anesthesia. The objective of the work has been to develop a
system which independently controls the intravenous infusion rates of the
hypnotic drug propofol and analgesic drug remifentanil. The system is de-
signed to track a reference hypnotic depth level, while maintaining adequate
analgesia. This is complicated by inter-patient variability in drug sensitiv-
ity, disturbances caused foremost by surgical stimulation, and measurement
noise. A commercially available monitor is used to measure the hypnotic
depthofthepatient,whileasimplesoftsensorestimatestheanalgesicdepth.
Bothinductionandmaintenanceofanesthesiaareclosed-loopcontrolled,us-
ingaPIDcontrollerforpropofolandaPcontrollerforremifentanil.Inorder
to tune the controllers, patient models have been identified from clinical
data, with body mass as only biometric parameter. Care has been taken
to characterize identifiability and produce models which are safe for the in-
tended application. A scheme for individualizing the controller tuning upon
completion of the induction phase of anesthesia is proposed. Practical as-
pects such as integrator anti-windup and loss of the measurement signal are
explicitly addressed. The validity of the performance measures, most com-
monly reported in closed-loop anesthesia studies, is debated and a new set
of measures is proposed. It is shown, both in simulation and clinically, that
PID control provides a viable approach. Both results from simulations and
clinicaltrialsarepresented.Theseresultssuggestthatclosed-loopcontrolled
anesthesia can be provided in a safe and efficient manner, relieving the reg-
ulatory and server controller role of the anesthesiologist. However, outlier
patient dynamics, unmeasurable disturbances and scenarios which are not
considered in the controller synthesis, urge the presence of an anesthesiolo-
gist. Closed-loop controlled anesthesia should therefore not be viewed as a
replacement of human expertise, but rather as a tool, similar to the cruise
controller of a car.
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Acknowledgments
ItiswiththedirectorindirecthelpfromseveralpersonsthatIhavecometo
write this thesis. With the reservation of forgetting anyone of you, I would
explicitly like to acknowledge the following persons.
My supervisor professor Tore Hägglund has been ever supporting in my
work. Your engagement and mentoring has meant a lot to me. You have
always encouraged me and contributed to an atmosphere in which it has
been truly enjoyable to work. You have also served as a role model, in a
much broader context than that of automatic control.
Professor Karl Johan Åström has been a great source of inspiration and
has been the source of several key ideas around which I have worked.
The administrative staff at the department, being Britt-Marie Mårtens-
son, Ingrid Nilsson, Eva Schildt, Agneta Tuszynski, Eva Westin, Monika
Rasmusson and Lizette Borgeram have all been very kind, knowledgeable
and helpful.
At the University of British Columbia I would like to acknowledge pro-
fessor Guy Dumont and post doctoral fellows Jin-Oh Hahn and Klaske van
Heusdenforintroducingmetoaninterestingresearchtopic.Iwouldalsolike
to thank Dr. Mark Ansermino and the staff at the anesthesia department of
the British Columbia Children’s Hospital in Vancouver.
I would like to thank all fellow PhD students at the department for in-
teresting discussions. In particular my former office mate Magnus Linderoth
hasprovidedmaterialfordiscussionsofalmosteverything,includingrelevant
topics.
ResearchengineersRolfBraun,PontusAndersson,AndersBlomdell,Leif
Andersson and Anders Nilsson have taught me many interesting things re-
lated to computers, lab processes and workshop machines which I am sure
will come to use regularly.
Finally I would like to thank my wife Ingrid, my family and my friends
in Lund and Vancouver.
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Acknowledgments
Financial Support
The Swedish Research Council through the LCCC Linnaeus Center is grate-
fully acknowledged for financial support.
8
Contents
Preface 11
Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 17
1.1 Clinical Anesthesia . . . . . . . . . . . . . . . . . . . . . . . 17
1.2 Drug Dosing Regimens . . . . . . . . . . . . . . . . . . . . . 25
1.3 The Traditional Patient Model . . . . . . . . . . . . . . . . . 31
2. Models for Control 41
2.1 Equipment Models . . . . . . . . . . . . . . . . . . . . . . . 41
2.2 Propofol Patient Model . . . . . . . . . . . . . . . . . . . . . 46
2.3 Remifentanil Patient Model . . . . . . . . . . . . . . . . . . 65
3. Control of Anesthesia 67
3.1 Performance Measures . . . . . . . . . . . . . . . . . . . . . 67
3.2 The iControl Study . . . . . . . . . . . . . . . . . . . . . . . 75
3.3 Simulation Studies . . . . . . . . . . . . . . . . . . . . . . . 84
3.4 Control of Analgesia . . . . . . . . . . . . . . . . . . . . . . 93
4. Discussion 102
4.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
4.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
References 105
Nomenclature 116
Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
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