title: Evaluation of a near-infrared spectrometer (NIRO 300) for the detection of intracranial oxygenation changes in the adult head.
abstract: OBJECTIVE
  The clinical application of intracranial near-infrared spectroscopy in adults has been hampered by concerns over contamination from extracranial tissues. The NIRO 300 (Hamamatsu Photonics) provides continuous online measurements of hemoglobin and cytochrome oxidase concentrations and a calculated tissue oxygen index (TOI). The present study seeks confirmation of the anatomic source of TOI in the adult cranium.
  
  
  METHODS
  Sixty patients undergoing carotid endarterectomy were studied. The NIRO 300 was incorporated into an established multimodal monitoring system. TOI, oxyhemoglobin, and deoxyhemoglobin changes were assessed and compared with (1) frontal cutaneous laser-Doppler flowmetry and (2) transcranial Doppler measurement of the ipsilateral middle cerebral artery flow velocity.
  
  
  RESULTS
  Changes in TOI were seen during cross-clamping of the carotid vessels in 49 patients (mean DeltaTOI=-9.4%, SD=7.1). Significant correlation was seen between TOI and flow velocity (r=0.56) but not with laser-Doppler flowmetry (r=0.13). In 31 patients, oxyhemoglobin and deoxyhemoglobin concentrations were recorded, showing significant changes during both external carotid artery and internal carotid artery clamping. A change in TOI was predominantly associated with internal carotid artery clamping (n=41). When TOI changed during external carotid artery clamping (n=8), significant blood pressure changes occurred, or extracranial-to-intracranial anastomosis was evident. In the absence of such variables, the sensitivity of TOI to intracranial and extracranial changes was 87.5% and 0%, respectively, and specificity was 100% and 0%, respectively.
  
  
  CONCLUSIONS
  The NIRO 300 reflects changes in cerebral tissue oxygenation when TOI is calculated, with a high degree of sensitivity and specificity.
authors.affiliation: University Department of Neurosurgery, Addenbrooke's Hospital, Cambridge, UK.
authors.forename: P G
authors.initials: PG
authors.lastname: Al-Rawi
authors.forename: P
authors.initials: P
authors.lastname: Smielewski
authors.forename: P J
authors.initials: PJ
authors.lastname: Kirkpatrick
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000033:anatomy & histology / Q000378:metabolism*; D001923:Brain Chemistry; D002545:Brain Ischemia / Q000175:diagnosis; D003576:Electron Transport Complex IV / Q000032:analysis; D016894:Endarterectomy, Carotid; D005260:Female; D006257:Head; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D017078:Laser-Doppler Flowmetry; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption; D010108:Oxyhemoglobins / Q000032:analysis; D012680:Sensitivity and Specificity; D019265:Spectroscopy, Near-Infrared / Q000295:instrumentation*; D017585:Ultrasonography, Doppler, Transcranial
chemical_list: D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin; D003576:Electron Transport Complex IV; D010100:Oxygen