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Re: Bispectral Index - smoothing interval
- Falk von Dincklage (7 April 2009)
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Bispectral Index - smoothing interval
- ARUN NATARAJAN, [Imran Ahmad], [Banu Nalla] (1 April 2009)
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Falk von Dincklage
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Dear Sir, Thank you for your interest in our work. We used the BIS and the RIII-reflex threshold to monitor the state of responsiveness to a noxious stimulus only without actually stimulating the subject with the noxious stimulus while collecting the BIS and RIII reflex values. The noxious stimulus was given after collecting the RIII and BIS values to check whether the two monitors were correct in predicting the response or not. Or in other words: we first measured BIS and RIII reflex threshold in the subjects at a stable state of anesthesia without giving any noxious stimulus. Then we calculated whether the two indices would predict a reaction or no reaction to a noxious stimulus. And then we gave the noxious stimulus to check whether the predictions were correct. In this study we did not analyze any changes of the BIS or RIII reflex threshold as a response to the noxious stimulus. The BIS values in the graph marked with no movement are the BIS values obtained before giving the noxious stimulus. Changes of the BIS after giving the stimulus were not included in our analysis. However, from a observational point of view I would agree that undelayed and delayed responses to the noxious stimulus do occur, which are reflected in the BIS. And to investigate these the smoothing interval of the BIS has to be taken into account as well as longer intervals after the stimulus. Yours sincerely, Falk von Dincklage Conflict of Interest:None declared |
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ARUN NATARAJAN, SpR, Anaesthetics Guy's & St Thomas' NHS Trust, [Imran Ahmad], [Banu Nalla]
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Editor-- We read with interest the article by von Dincklage and colleagues [1], who compared the nociceptive flexion threshold and the Bispectral index (BIS) as monitors of movement responses to noxious stimuli under propofol mono-anaesthesia. In particular we were interested in the use of the bispectral index in this study. Bispectral index has a smoothing interval ranging from 15-30seconds, depending on the model used [2], This means only 15 or 30 seconds after the verbal or noxious stimulus is applied, the BIS value will reflect a change in response to the stimulus. In this study the BIS values associated with noxious stimulus for no movement is around 27 (from the graph). In our practice we have seen patients move under propofol mono-anaesthesia, but there is a 30 second lag before a corresponding change is seen on the BIS. We would like to know if the authors took the smoothing interval into consideration while recording the BIS values in this study. Reference: 1. F. von Dincklage, K. Send, M. Hackbarth, B. Rehberg, and J. H. Baars Comparison of the nociceptive flexion reflex threshold and the bispectral index as monitors of movement responses to noxious stimuli under propofol mono-anaesthesia. Br. J. Anaesth. 2009; 102: 244-250 2. V. Bonhomme, P. Hans. Monitoring depth of anaesthesia: is it worth the effort? Review article. European Journal of Anaesthesiology 2004; 21: 423-428 Conflict of Interest:None declared |
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