We thank Grocott and Davie1  for their interest in spatially resolved near-infrared spectroscopy (SR-NIRS) evaluation of cerebral oxygenation and for their unique evaluation of skin influence on three commercially available SR-NIRS systems. We acknowledge that our findings may not apply to all SR-NIRS systems, and although unintended, the title of the article may be too general. Throughout the discussion and the conclusion, however, we meticulously specify that it is the INVOS machine that is evaluated.2  At the same time, we understand that Grocott and Davie1  suggest that cutaneous oxygenation affects evaluation not only by INVOS but also by Foresight and EQUANOX. We find it likely that vasoconstriction observed during administration of noradrenaline exerts a similar impact on the SR-NIRS–determined frontal lobe oxygenation as scalp ischemia.1  Cerebral blood flow or oxygenation was not measured in that study, but we find it unlikely that headband occlusion of skin blood flow influences cerebral variables and the reduction in SR-NIRS evaluation of cerebral oxygenation is, therefore, most likely explained by a flawed SR-NIRS methodology. Taken together, the evidence obtained by different experimental approaches1,2  suggests that not only the INVOS SR-NIRS is affected by cutaneous contamination of the signal. In fact, on-going evaluation suggests that INVOS SR-NIRS is less affected by skin oxygenation than other systems, although we, obviously, have not evaluated the influence of skin oxygenation on all SR-NIRS apparatus.

References

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