An Overview of TCI and TIVA. By Anthony R. Absalom, M.D. and Michel M. R. F. Struys, M.D., Ph.D. Ghent, Belgium, Academia Press, 2005. Pages: 88. Price: Approximately 15.00 Euros (U.S. $28.50).
“An Overview of TCI and TIVA” was written by two pioneers in the field of targeted drug delivery in anesthesia. Despite its small size, this book is a rich source of information on the structure, function, and clinical applications of target-controlled infusion (TCI) systems. Discussions on manually controlled infusion regimens of the most popular agents are not omitted either. A large number of data are presented in a concise yet comprehensive manner, and helpful clinical guidance is often provided. Important pharmacokinetic and pharmacodynamic principles, which relate to the operational standards of TCI systems, are analyzed in chapters II and III, whereas explicit references to pharmacokinetic and pharmacodynamic functions are made throughout the book. The language, although nonmathematical, relays a scientific strength. The presentation is simple, but not simplistic. The text has the appearance of “class notes” rather than a formal manual; however, this feature enhances the tutorial dynamics of the book and should attract individuals involved in learning such as anesthesia residents and specialists flirting with total intravenous anesthesia (TIVA). Although not stylish, the 21 figures and diagrams are succinct and help the reader visualize drug disposition and understand TCI dynamics for commonly used agents. The few errors in the figures and text are easily noticeable and not misleading.
In their opening remarks, the authors argue the potential advantages of TIVA over inhalation anesthesia. Although current technology still operates far from realizing the concept of an “intravenous vaporizer,” TCI systems have been developed and are being improved continually to enable accurate and efficient anesthetic control.
In chapter I, the authors focus on the definition, development, and functional components of TCI systems. A distinction is made between open-loop operators and closed-loop control systems, while a simple case of plasma controlled infusion is analyzed through the bolus-elimination-transfer principle. The authors, with references from the relevant literature, argue that TCI is preferable to manually controlled infusions because of the improved safety and efficacy of intravenous anesthetic. However, there is still an obvious lack of compelling evidence that a TCI approach is clinically superior to manual control of anesthesia. A description of the different types of controls used in TCI systems is missing. The authors represent two different schools on control methodology used in TCI applications: One is the proportional-integral-derivative technique, and the other is model-based, patient-adaptive control. Issues such as the engineering principles of various control methods or characteristics of optimum control for TCI applications could have been discussed. Despite its attractive simplicity, the general level of the book is high, and some additional, in-depth analysis of the issues above would certainly interest at least research-oriented readers.
In chapter II, a short introduction to basic kinetic principles is followed by comments on pharmacokinetic models for commonly used TCI agents. The authors do not elaborate on the kinetics of individual agents, but they do provide useful clinical information mostly by comparing different pharmacokinetic models for the same agent. For example, the effect of covariates like age, weight, and sex on the kinetics of various agents is discussed, while five tables at the end of the book provide a complete account of the most popular pharmacokinetic and pharmacodynamic models for commonly used agents. The next three sections of this chapter, “Accuracy of target-controlled infusion systems,”“Which patient weight should be used for TIVA and TCI?” and “Effect-site targeting, time to peak effect and ke0,” go further and deeper in TCI analysis. Such high-quality, processed knowledge is difficult to dissect out of a “busy” textbook or the technical text of a scientific paper. Creative anesthetists and junior investigators will find these sections especially appealing. The authors analyze, among others, the TCI mechanics of effect site targeting using different time constants but the same pharmacokinetic sets. Clinical meaning is provided through plenty of paradigms and graphs.
Chapter III deals with the pharmacodynamics of propofol and opioids. Sedation and anesthesia are examined separately, while much space is devoted to reporting concentrations for various end points from different studies. The value of this report is doubtful, because the interindividual variability in pharmacodynamics is high and the authors rightfully advice TCI operators to use titration. Surrogate measures of drug effect and methods of pharmacodynamic analysis are missing. Nonetheless, important pharmacodynamic information (e.g. , time to peak effect principle and effect site targeting) was presented as part of the effect site targeting discussion in chapter II. The section on pharmacodynamic interactions and their potential clinical implications is nicely written.
Chapter IV is dedicated to practical aspects of TIVA and TCI operation. Sections dealing with manually controlled infusions for propofol and opioids will certainly interest anesthetists residing in the United States, because their access to TCI technology is limited to the investigational arena. The presented material, though, is inadequate. Obvious reasons are the complicated calculations required for the various infusion algorithms and the limited research in the field. The clinical management of blood– and effect site–targeting infusions in “healthy” and “high-risk” patients is described in an instructive manner, while six case studies presented in the last chapter are also helpful to that end. Much of the perioperative information not directly related to the management of TIVA could have been omitted. On the other hand, enrichment of this series with more challenging cases (e.g. , awake fiberoptic intubation in normal-weight or obese patients, awake craniotomy, patients with sleep-disordered breathing, and postoperative pain management) would be more likely to set off the clinical benefits and problems of automated drug delivery.
In conclusion, I found this booklet quite valuable. Anesthetists who ask questions about the physiology and clinical applications of TCI systems will find most of the answers they need in this book. TIVA lovers will get the stimulation to try something new. Junior investigators in the field will find certain parts of the text very enlightening, as well as thought provoking.
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