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REPLY

Montreal Heart Institute, Montreal, Canada, E-mail: marie-christine.taillefer{at}icm-mhi.org

We thank Dr. Nollert for his comments. It is unfortunate that his publications,^1,2 as well as one of a colleague,³ were not identified using our search strategy. Our selection of keywords did not include "spectrophotometry" or the abbreviation for near-infrared spectroscopy "NIRS" in the literature search.

We do not agree with Dr. Nollert’s comment concerning a selection bias of articles. We did verify the reference list of the Somanetics^TM website. However, as he rightly pointed, there was a risk that this strategy would generate only papers with positive results. To avoid this problem, we augmented our search strategy with several Medline searches and reviews of secondary references. In addition, all the references taken from the website were also retrieved by other means [Medline, journal home page, meeting home page (abstracts) or pdf files]. We also considered in our review⁴ papers on the clinical efficacy of the NIRS using the Hamamatsu^TM (NIRO) devices. Consequently, we believe that we took the necessary steps to minimize selection bias. Although animal studies were not the focus of our review,⁴ Dr. Nollert is correct to suggest that they are important for evaluation of new technologies. As he points out, very few animal studies have been performed with the Somanetics^TM device.

As highlighted in the discussion of our review,⁴ NIRO^TM and Somanetics^TM INVOS devices used different methods of data management, the former being quantitative and the latter qualitative. Dr. Nollert identified that other surgical parameters, including hemodilution and deep hypothermic circulatory arrest, should be taken into account when one wants to measure brain oxygenation during cardiac surgery. Both types of devices are in development and have technical limitations that need to be addressed before they can be used clinically on a regular basis. We are confident that Dr. Nollert’s work as well as our own, despite the identified limitations, will help foster the identification of strengths and weaknesses of both types of NIRS devices, and allow for the development of more valid instruments. This technology may have clinical applications in monitoring patients at risk from brain insult due to surgery, but more research is clearly indicated.

References

1 Nollert G, Mohnle P, Tassani-Prell P, Reichart B. Determinants of cerebral oxygenation during cardiac surgery. Circulation 1995; 92: II327–33.

2 Nollert G, Mohnle P, Tassani-Prell P, et al. Postoperative neuropsychological dysfunction and cerebral oxygenation during cardiac surgery. Thorac Cardiovasc Surg 1995; 43: 260–4.[Medline]

3 Tamura M. Non-invasive monitoring of brain oxygen metabolism during cardiopulmonary bypass by near-infrared spectrophotometry. Jpn Circ J 1991; 55: 330–5.[Medline]

4 Taillefer MC, Denault AY. Cerebral near-infrared spectroscopy in adult heart surgery: systematic review of its clinical efficacy. Can J Anesth 2005; 52: 79–87.[Abstract/Free Full Text]

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