Correspondence  |   October 2016
In Reply
Author Notes
  • Montreal Heart Institute, University of Montreal, Montreal, Quebec, Canada.
  • (Accepted for publication June 21, 2016.)
    (Accepted for publication June 21, 2016.)×
Article Information
Correspondence   |   October 2016
In Reply
Anesthesiology 10 2016, Vol.125, 819-820. doi:10.1097/ALN.0000000000001256
Anesthesiology 10 2016, Vol.125, 819-820. doi:10.1097/ALN.0000000000001256
We thank Drs. Fellahi and Portran for bringing attention to these important issues and for putting into context some of the methods leading to the results obtained in our feasibility study. The main purpose of the feasibility trial was to verify that the high rate of success of reversal of cerebral desaturations obtained in our single-center study1  (88% of patients) could be repeated in centers that would eventually participate in a multicenter randomized controlled trial on the benefit of reversal of cerebral desaturations on patient outcomes in cardiac surgery. While discussing the methodology to adopt for the feasibility trial, we came to realize that after years of using this technology, it has become routine to start interventions to bring cerebral saturation back to normal values well before the full 20% decrease from baseline is reached. We, therefore, wanted to ask the question, do early interventions on cerebral desaturations help to avoid the progression of desaturations below the 20% threshold from baseline? If most of the variations within 10% of baseline are noise or extracranial contaminations, interventions should not impact on further progression to 20% baseline values. Our results show that early interventions prevented further decreases from 10 to 20% of baseline.2  Only 48% of patients in the intervention group had desaturations continue decreasing below 20% baseline, while almost all patients without interventions (82%) went on to desaturations below 20% baseline. We still considered 20% baseline the threshold for significant desaturations and calculated the cerebral desaturation load (area under the curve of cerebral desaturation over time) from this level. Early interventions are probably the reason why the reversal rate per patient was even higher (97%) than in our previous study. If extracranial contamination for the devices is within 10% of baseline value, why would interventions at this level matter for further desaturations? To answer this question, we have to look at the methodology used in the feasibility trial, desaturations had to last at least 15 s or more before interventions were started, and this is a long enough time to exclude most variations due to noise or extracranial contamination. Furthermore, in Davie and Grocott’s study,3  in order to estimate extracranial contamination, a pneumatic cuff had to be inflated around the head to unmask skin blood flow, which is considered contamination. Without cuff inflation, the skin contamination is just part of the signal, and we have no reason to believe that skin blood flow was specifically affected independently of cerebral blood flow in our study. Therefore, in a multicenter, prospective randomized control trail on the impact of reversing decreases in cerebral saturation on outcomes, we would very likely use the 10% threshold for intervention and 20% threshold for significant desaturation as we did in the feasibility study.
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