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Spectroscopy
Volume 17 (2003), Issue 2-3, Pages 289-295
http://dx.doi.org/10.1155/2003/627858

Simultaneous pO2 and HbO2 measurement to determine absolute HbO2 concentration for in vivo near infrared spectroscopy

Andrew J. Macnab,2 Roy Gagnon,1 Faith Gagnon,1 Andrew I. Minchinton,1 and Karen H. Fryer1

1Department of Pediatrics, British Columbia's Children's Hospital, University of British Columbia, Vancouver, Canada
2Division of Critical Care, Room 2L5, BC Children's Hospital, 4480 Oak Street, Vancouver, BC, V6H 3V4, Canada

Copyright © 2003 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose: Near infrared spectroscopy (NIRS) monitors absolute changes in concentration of chromophores from an unquantified baseline. A change in oxygenation is required to obtain information. Clinically, knowing initial chromophore concentration is desirable. We sought absolute initial concentrations by combining NIRS measurements with simultaneous Eppendorf histograph measurement (absolute values of tissue partial pressure of oxygen (pO2)). Methods: There were 22 trials on 9 occasions in 2 adult volunteers. Following local anaesthetic, the histograph probe was inserted into the forearm muscle and NIRS optodes applied. A sphygmomanometer cuff was inflated over the upper arm to produce ischaemia and hypoxia. Change in pO2 was determined as a percentage of the initial pO2. Change in HbO2 was measured, and the initial HbO2 calculated by assuming the percentage change in HbO2 equaled the percentage change in pO2. Results: Mean percentage change in pO2 was 20.7 ± 9.6. Mean change in HbO2 was 22.4 ± 3.4 µmol/l(tissue). Calculated initial HbO2 was 146.4 ± 108.7 µmol/l(tissue), range 51 to 508 µmol/l(tissue). Correlation (r2) between pO2 and HbO2 was 0.97 ± 0.03. Conclusion: Although changes in pO2 and HbO2 were highly correlated, calculation of initial absolute concentration of HbO2 was not achieved by this method. A reliable method of obtaining absolute concentrations of HbO2in vivo remains to be found.