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J Thorac Cardiovasc Surg 2006;132:1172-1178
© 2006 The American Association for Thoracic Surgery

Evolving Technology

Relevance of depth resolution for cerebral blood flow monitoring by near-infrared spectroscopic bolus tracking during cardiopulmonary bypass

Jens Steinbrink, PhDa,*, Thomas Fischer, MDc, Hermann Kuppe, MDc, Roland Hetzer, MDd, Kamil Uludag, PhDa, Hellmuth Obrig, MDa, Wolfgang M. Kuebler, MDb,c

a Clinic of Neurology, German Heart Institute, Berlin, Germany
b Institute of Physiology, German Heart Institute, Berlin, Germany
c Charité–Universitaetsmedizin and the Departments of Anesthesiology, German Heart Institute, Berlin, Germany
d Cardiothoracic and Vascular Surgery, German Heart Institute, Berlin, Germany.

Received for publication February 3, 2006; revisions received May 8, 2006; accepted for publication May 18, 2006.

* Address for reprints: Jens Steinbrink, Charité University Hospital, Clinic of Neurology, Schumannstrasse 20/21, 10098 Berlin, Germany. (Email: jens.steinbrink{at}charite.de).

OBJECTIVE: Noninvasive near-infrared spectroscopy (NIRS) is increasingly used to monitor cerebral oxygenation and blood flow status, which is also of high relevance during cardiovascular surgical interventions with cardiopulmonary bypass. Contamination of the cerebral signal by contamination from overlaying extracerebral tissue, however, has been proposed to reduce sensitivity and cerebral selectivity of this promising technique.

METHODS: We evaluated a novel depth-resolved approach for the determination of cerebral hemodynamics by near-infrared spectroscopic tracking of intravenously administered indocyanine green boluses. A frequency domain technique was applied, allowing simultaneous determination of light absorption changes and time of flight of single photons and enabling the differentiation between extracerebral and intracerebral tracer kinetics. Depth-resolved near-infrared spectroscopy was tested in 4 patients undergoing cardiopulmonary bypass and compared with data derived by conventional continuous-wave near-infrared spectroscopy.

RESULTS: Depth resolution extracted the differential responses of extracerebral and intracerebral blood vessels from near-infrared bolus tracking signals. Postoperative blood flow indices derived from the intracerebral time course exceeded preoperative values by 1.5 ± 0.2 times, indicating a significant increase of cerebral blood flow not detectable by conventional near-infrared spectroscopy.

CONCLUSION: The depth-resolved approach provides additional and relevant data for the interpretation of intraoperative cerebral perfusion during cardiothoracic surgery. The validity of this approach for patients with preexisting risk factors for cerebral hypoperfusion remains to be determined in larger clinical trials.

Abbreviations and Acronyms {Delta}cICG = change in indocyanine concentration; {Delta}µa = absorption change; BFI = blood flow index; CBF = cerebral blood flow; CPB = cardiopulmonary bypass; ICG = indocyanine green; NIRS = near-infrared spectroscopy




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J Appl Physiol, April 1, 2008; 104(4): 905 - 906.
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