To the Editor:

In the August issue of Anesthesiology, I found two articles of particular interest regarding propofol administration.1,2I was simply confounded by the fact that target-controlled infusion (TCI) “predicted” concentrations have become the basic jargon for scientific papers. In both articles, I never found any TRUE raw data disclosing the actual dose of drug administered to these patients. In addition, the index of anesthesia in the article by Rigouzzo et al.  2was the bispectral index value (another proprietary, i.e. , undisclosed program). In particular, the article by Rigouzzo et al.  2demonstrated that true differences exist between the multiple studied TCI models (and probably all others as well). I was confounded for several reasons: (1) TCI is not currently used in the United States and probably will remain withheld from clinical use by the Food and Drug Administration; (2) there apparently are multiple TCI devices with unknown (to any U.S. clinician) validity and deviations in ability/accuracy; and (3) TCI values are predictions  and not measured values in any individual study; (4) multiple variables influence actual  plasma concentrations in any given patient or patient group; and (5) finally, the actual TCI infusion rates change over time. Our journal (Anesthesiology) is a publication of the American Society of Anesthesiologists, where practice remains relevant in terms of microgram per kilogram per minute during propofol infusion. It would seem appropriate to require, at a bare minimum, presentation of this pertinent information to the readership (at least alongside TCI values) for several reasons: (1) microgram per kilogram per minute is the American “frame of reference”; (2) microgram per kilogram per minute is REAL and not proposed/extrapolated scientific information; and (3) TCI devices should/must disclose the instantaneous infusion rate during the relevant study periods.

Although I understand the practicability of “indexing anesthetic depth” to some form of electroencephalogram monitor for studies for total intravenous anesthesia anesthetics, I would hope the Journal  would also require end-tidal gas concentration disclosure for any inhaled agent mentioned in a manuscript. As a clinical scientist, it is essential to know  what is actually  being administered to correlate to truly dependent variables such as bispectral index or TCI, especially because no single electroencephalogram monitor or TCI program has been accepted as the standard for scientific studies or even clinical use in the United States. I concluded that I simply came away from both articles without meaningful clinical information—clinical information being why I read this journal. I personally suspect Bandschapp et al.  1found “analgesic properties of propofol” simply because pain is the conscious  perception of noxious stimulation, and impairment of consciousness resulted in these findings (with probably 60 microgram per kilogram per minute of propofol infusing). Perhaps Anesthesiology might lead the world's journals to take on such a basic standard of presenting facts (infusion rates) instead of predictions (TCI/bispectral index) as basic science and in the interests of our readership.

Cleveland Clinic, Cleveland, Ohio.


Bandschapp O, Filitz J, Ihmsen H, Berset A, Urwyler A, Koppert W, Ruppen W: Analgesic and antihyperalgesic properties of propofol in a human pain model. Anesthesiology 2010; 113:421–8
Rigouzzo A, Servin F, Constant I: Pharmacokinetic-pharmacodynamic modeling of propofol in children. Anesthesiology 2010; 113:343–52