Correspondence  |   August 2018
In Reply
Author Notes
  • University of Oxford, Oxford, United Kingdom (C.E.W.). katie.warnaby@ndcn.ox.ac.uk
  • (Accepted for publication May 7, 2018.)
    (Accepted for publication May 7, 2018.)×
Article Information
Correspondence
Correspondence   |   August 2018
In Reply
Anesthesiology 8 2018, Vol.129, 375-377. doi:10.1097/ALN.0000000000002289
Anesthesiology 8 2018, Vol.129, 375-377. doi:10.1097/ALN.0000000000002289
We thank Colin et al. and Schwartz for their interest in our recently published work in Anesthesiology.1  In the referenced manuscript, we fitted slow-wave activity drug dose-response curves to electroencephalographic data acquired during anesthesia in a propofol healthy volunteer study and three patient studies. By applying these techniques to induction and emergence, we presented two distinct, but related, findings.
First, as described by Schwartz, we confirmed that our experimental finding of slow-wave activity saturation2  also occurs during surgical anesthesia. While we entirely agree that exploration of the transition to burst suppression is important, this was not the focus of our article. Slow-wave activity saturation occurs at considerably lower levels of anesthesia than burst suppression (fig. 1G of Warnaby et al.1 )—hence why the presence of burst suppression was considered to be artefactual in the fitting of slow-wave activity–concentration curves. Furthermore, we did not imply that muscle relaxants have no influence on the electroencephalogram, only that they had no influence on the slow-wave activity saturation parameters (i.e., the power and concentration of slow-wave activity saturation, defined by the electroencephalographic dose-response curve fit). Neuromuscular blocking drugs certainly influence the electroencephalogram and, in particular, frequencies above 20 Hz,3  but we are unaware of any evidence that neuromuscular blockade potentiates burst suppression in humans. The prerequisites for inclusion of patient data in our analyses were specified in the Materials and Methods section. Any small discrepancies in N were due to the original data not meeting the criteria for inclusion in this different analysis with different criteria.
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