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LETTERS TO THE EDITOR

Remifentanil Manual Versus Target-Controlled Infusion

Peninsula Medical School, Plymouth, United Kingdom

To the Editor:

De Castro et al. (1) compared manual and target-controlled infusions (TCI) of remifentanil in patients undergoing carotid endarterectomy. Unfortunately, their studies design may have prejudiced its outcome.

The manual and TCI schemes are not comparable; in particular, the titration steps in the manual scheme (0.05 µg · kg^-1 · min^-1) were very small. Clearly TCI and manual schemes can never be the same but some prestudy simulations might have improved the study design. Simulations of their protocol using either no titrations (Fig. 1) or two downward titrations (Fig. 2) show that in each case the predicted remifentanil concentrations are much higher in the manual scheme. This is reflected in the results with almost twice as much remifentanil given to patients in the manually infused group. In light of this differential dosing, the finding of less hypotension with TCI is hardly surprising. The authors have demonstrated that remifentanil causes dose-related hypotension in elderly arteriopaths. A less misleading title for the study might be "Reduce the dose of remifentanil to minimize hypotension in the elderly"! TCI is a valuable and well-established technique for propofol anesthesia. Remifentanil is simple to use and well suited to manual infusion schemes and the case for the Remifusor remains unproven. If remifentanil TCI has a real clinical advantage then it must be demonstrated in more even-handed comparisons.

View larger version (15K): [in this window] [in a new window]   Figure 1. Simulation of the plasma and effect site concentrations achieved in the manual and target-controlled infusion groups. Note that in the absence of titrations the manual infusions achieve much higher concentrations from 4 min onward.

View larger version (16K): [in this window] [in a new window]   Figure 2. Simulation of the plasma and effect site concentrations achieved in the manual and target-controlled infusion groups; in each scheme two incremental decreases have been made at around 3 and 5 min. Note that the manual infusions achieve much higher concentrations from 4 min onward.

1. De Castro V, Godet G, Mencia M, et al. Target-controlled infusion for remifentanil in vascular patients improves hemodynamics and decreases remifentanil requirement. Anesth Analg 2003; 96: 33–8.[Abstract/Free Full Text]

Response

Department of Anesthesiology, Pitié-Salpêtrière Hospital, Paris, France

In Response:

We thank Dr. Sneyd for his interest and comments concerning the paper about TCI for remifentanil in patients undergoing carotid endarterectomy.

To summarize his comments, remifentanil should be reduced to minimize hypotension in the elderly (and arteriopath). We do agree with this known statement, but should it be achieved blindly or in a more accurate way? We supposed TCI for remifentanil could be an useful tool to minimize hemodynamic events related to drug administration by reducing dosing and smoothing its administration compared with manual infusion. The administration modalities used in the manual infusion group were in accordance with the laboratory’s specifications and classical administration schemes. In order to make groups comparable at the induction of anesthesia, the effect-site concentration was fixed at 4 ng/mL in the TCI group, a concentration also achieved in the manual infusion group in the delay close to tracheal intubation, as shown in Figure 1 in Dr. Sneyd’s letter. Then it should be kept in mind that adaptation of infusion is focused on the common objective of hemodynamic stability within 30% range of the patient’s preoperative values of blood pressure and heart rate in both groups. Once this clinical effect is defined, the adequate drug concentration to achieve this effect should be the lowest, and the best administration modality the one that permits the finest adaptation. As mentioned and shown in Figure 2 in Dr. Sneyd’s letter, the titration steps in the manual scheme are very small. The purpose was to adapt smoothly manual infusion to the patient’s requirement like TCI does, even if it requires surely more than two adjustments. Dr. Sneyd also implicitly extrapolates the observation of higher concentrations of remifentanil in the manual infusion group compared with TCI within the short period of induction to explain our result in total dose consumption of remifentanil between groups. Even if it is convenient, this does not explain our result reflecting many adaptations of infusion (decrease but also increase) in both groups within the approximately 2 h of anesthesia. Certainly TCI should be improved, and its clinical impact compared with manual infusion remains to be evaluated, but we should not minimize its importance for elderly patients.

This article has been cited by other articles:

				J.-S. Nho, S.-Y. Lee, J.-M. Kang, M.-C. Kim, Y.-K. Choi, O.-Y. Shin, D.-S. Kim, and M.-I. Kwon Effects of maintaining a remifentanil infusion on the recovery profiles during emergence from anaesthesia and tracheal extubation Br. J. Anaesth., December 1, 2009; 103(6): 817 - 821. [Abstract] [Full Text] [PDF]

				J. R. Sneyd Recent advances in intravenous anaesthesia Br. J. Anaesth., November 1, 2004; 93(5): 725 - 736. [Abstract] [Full Text] [PDF]

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