title: Relevance of depth resolution for cerebral blood flow monitoring by near-infrared spectroscopic bolus tracking during cardiopulmonary bypass.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Clinic of Neurology, German Heart Institute, Berlin, Germany. jens.steinbrink@charite.de
authors.forename: Jens
authors.initials: J
authors.lastname: Steinbrink
authors.forename: Thomas
authors.initials: T
authors.lastname: Fischer
authors.forename: Hermann
authors.initials: H
authors.lastname: Kuppe
authors.forename: Roland
authors.initials: R
authors.lastname: Hetzer
authors.forename: Kamil
authors.initials: K
authors.lastname: Uludag
authors.forename: Hellmuth
authors.initials: H
authors.lastname: Obrig
authors.forename: Wolfgang M
authors.initials: WM
authors.lastname: Kuebler
mesh_terms: D000368:Aged; D001783:Blood Flow Velocity; D002315:Cardiopulmonary Bypass; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D007202:Indicators and Reagents; D007208:Indocyanine Green; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D019265:Spectroscopy, Near-Infrared
chemical_list: D007202:Indicators and Reagents; D007208:Indocyanine Green