Target-controlled infusion devices: are we missing much?

Abstract

Total intravenous anesthesia is probably less popular in North America than in other parts of the world, perhaps because of limited access in Canada and the United States to target-controlled infusion (TCI) devices to deliver intravenous drugs, such as propofol and remifentanil. The principle of operation of commercially available TCI devices, such as the Diprifusor , (Astra-Zeneca Pharmaceuticals, Macclesfield, UK) is rather simple. The operator selects a target plasma concentration of drug (e.g., propofol) that the patient requires for a specified procedure, and the TCI device automatically administers a small bolus loading dose followed by a kinetically driven infusion rate to rapidly attain and then maintain that drug concentration until a new drug concentration is selected. The TCI device informs the anesthesiologist in real time of the population-based theoretical drug plasma concentration attained and the quantity of drug delivered. It is also possible to set TCI devices to target effect-site concentrations. In this case, the infusion rate takes into account the time lag between the plasma and the site of action (e.g., the brain in the case of hypnotics and opioids). In the United States, the Food and Drug Administration did not deem TCI devices sufficiently advantageous in anesthesia to approve their commercial use, and the devices are also not currently available in Canada. Are we being deprived of a truly useful tool to improve delivery of intravenous anesthetics, or are these devices merely gadgets that are useful in the research arena but much less so in the clinical setting? At first glance, the concept of the TCI device is clinically appealing. The anesthesiologist enters the patient’s covariates (age, weight, and height) with a population kinetic data set from a selection menu; the TCI device then calculates and delivers in real time the correct amount of drug that will rapidly achieve the desired target plasma or effect-site drug concentration. Whenever a new drug concentration is selected, the TCI calculations consider all drug history to achieve the new target concentration as soon as possible. There is no need to adjust the infusion rate to take into consideration complex pharmacokinetic redistribution and elimination processes or effect site time lag – the machine does all of this for you! Users of TCI devices do not think in terms of bolus doses and infusion rates, but rather in terms of target concentrations. Some users have pushed the concept even one step further and used TCI devices in their research to explore relationships between a concentration and a desired effect, such as loss of consciousness or specific bispectral index (BIS) targets. In this issue of the Journal, Austrian and Chinese groups collaborated to examine the responses to propofol when using this technology in two different patient populations. Their findings suggest that Chinese patients were more sensitive to propofol than Austrian patients. Their study can be viewed as an example of the advantages and limitations of TCI devices. The authors administered propofol to all patients in the same manner, but instead of giving a certain dose or a certain dose per kilogram, they programmed the TCI device, in this case the Diprifusor , to achieve a target F. Donati, MD, PhD (&) Departement d’anesthesiologie, Hopital MaisonneuveRosemont, Universite de Montreal, 5415, boul l’Assomption, Montreal, QC H1T 2M4, Canada e-mail: francois.donati@umontreal.ca