To the Editor:—
The above letter was sent to the author of the referenced Editorial. The author did not feel that a response was required.—Michael M. Todd, Editor-in-Chief
In the article by Johnson et al. 1and in the follow-up editorial by Shafer2, the sensitivity of pigs to propofol after severe hemorrhage is described. In the editorial, the “take-home message” is that propofol is a poor choice for induction. My supplementary “take-home” message is that a monitor of anesthetic depth, such as the Bispectral Index, should be used for all critically ill patients. If a dose of propofol drives the Bispectral Index to 0 (isoelectricity), the patient is probably too deeply anesthetized. Certainly, it is possible that the Bispectral Index is not accurate during shock, i.e. , a decrease in Bispectral Index score might not necessarily represent a change in depth of anesthesia. In a case report of a patient who underwent elective abdominal aortic aneurysm repair with total intravenous anesthesia, the Bispectral Index score decreased shortly after the aortic clamp was released; 10 min later other monitored variables suggested clinical deterioration.3Although no study has formally analyzed the relationship of Bispectral Index to shock, there are electroencephalographic changes during shock. In awake animal studies of controlled hemorrhagic shock, electroencephalography frequency slows and amplitude increases; the electroencephalograph is flat when blood pressure is inadequate to support respiration.4–6It is not always clear how much anesthesia critically ill patients need. In such situations, I use a depth of anesthesia monitor, use much less anesthesia than I would otherwise have planned to use, and I believe that I also have an easier job of managing blood pressure.
University of Iowa, Iowa City, Iowa. lance-lichtor@uiowa.edu
