Tissue Oxygen Index

Abstract

Background and Purpose-To date, the clinical application of near infrared spectroscopy in the adult brain has been limited. The NIRO 300 (Hamamatsu Photonics) provides a continuous measurement of tissue oxygen index (TOI) using spatially resolved spectroscopy. Although TOI reflects cerebral oxygenation to a high degree of sensitivity and specificity, to become a useful clinical tool, thresholds for cerebral ischemia need to be defined. This study has attempted to identify a quantifiable TOI threshold for ischemia in the adult brain. Methods-One hundred sixty-seven patients undergoing carotid endarterectomy were studied. The NIRO 300 was incorporated into an established multimodal monitoring system enabling observations of cerebral hemodynamic changes under highly controlled conditions. Changes in TOI (%⌬TOI) on clamping the internal carotid artery were compared with intracranial blood flow (middle cerebral artery flow velocity) and cerebral function monitoring to identify and quantify periods of cerebral ischemia. Results-Significant correlation was seen between changes in middle cerebral artery flow velocity and ⌬TOI on clamping (rϭ0.74, Pϭ0.0001). Thirty-one patients showed cerebral ischemia on internal carotid artery clamping as defined by a sustained fall in cerebral function monitoring. A threshold for %⌬TOI of Ϫ13 was identified, above which no patients showed any evidence of ischemia on clamping. This threshold provided 100% sensitivity and 93.2% specificity for patients satisfying the preset criteria for cerebral ischemia. Conclusions-These data demonstrate the potential to identify TOI-quantified thresholds for cerebral ischemia in the adult brain and thus improve the clinical use of near infrared spectroscopy. Our observations have defined a drop in TOI (13%) that can be adopted as a threshold for severe cerebral ischemia with high sensitivity and specificity. Key Words: carotid endarterectomy Ⅲ cerebral ischemia Ⅲ near infrared spectroscopy Ⅲ spatially resolved spectroscopy Ⅲ tissue oxygen index O ptical methods based on near-infrared spectroscopy (NIRS) can be used to monitor hemodynamic variables in the clinical setting. 1 Applications include monitors of fetal physiology, 2-4 during cardiac surgery, 5,6 muscle function, 7-10 and neonatal, 11 pediatric, 12 and adult brain. [13][14][15][16][17][18][19] A number of NIRS instruments are now available that detect changes in optical attenuation from several wavelengths of light, and although a variety of algorithms have been applied to attempt quantification, accuracy of these instruments remains a concern.The NIRO 300 (Hamamatsu Photonics) provides a continuous online measurement of tissue oxygen index (TOI) using spatially resolved spectroscopy. 20,21 We have previously determined that TOI reflects cerebral oxygenation to a high degree of sensitivity and specificity during carotid surgery, 20 an indication that NIRS can show clinically relevant estimations of cerebral hemodynamic and oxygen changes in the adult head (Figure 1). However, there are no da...

Near-Infrared Spectroscopy in the Monitoring of Adult Traumatic Brain Injury: A Review

“…The TOI (expressed as a percentage index) is calculated using depth resolved total tissue Hb alongside the relative concentrations of OHb and HHb as identified by the relative NIRS tissue absorbance. 10,22 It has been demonstrated to be a useful guide to the threshold of cerebral ischemia and a reflection of cerebral tissue oxygenation specifically in certain circumstances. 22 Lam and coworkers 23 demonstrated that a 13% decrease from baseline of the TOI was 100% sensitive and 93.2% specific in detecting clinically significant cerebral oxygen desaturation.…”

“…10,22 It has been demonstrated to be a useful guide to the threshold of cerebral ischemia and a reflection of cerebral tissue oxygenation specifically in certain circumstances. 22 Lam and coworkers 23 demonstrated that a 13% decrease from baseline of the TOI was 100% sensitive and 93.2% specific in detecting clinically significant cerebral oxygen desaturation. This was established by the decrease in cerebral function (intraoperative cerebral function monitoring) during carotid artery clamping and bypass at endarterectomy using the Hamamatsu NIRO 300 NIRS monitor (space/distance resolved).…”

“…Importantly, this investigation made significant progress in resolving component contributions from the external carotid artery (ECA) and internal carotid (ICA), minimizing the often confounding surface effect of skin and other extracranial tissue perfusions that have been described. 20,22,24 The THI is an NIRS output parameter derived largely from a depth resolved combined tissue Hb signal strength 20 and has been utilized primarily to provide a surrogate for total tissue Hb content within the observed tissue. Intuitively, this is not entirely accurate, as the exact total volume of tissue under observation through the absorption of the emitted light is not known (it is therefore expressed as an arbitrary unit), although educated estimates have been formulated through novel computational modelling processes.…”

Inconsistent detection of changes in cerebral blood volume by near infrared spectroscopy in standard clinical tests

“…NIRS optodes were set at a distance of 5 cm by a rubber holder secured to the skin by biadhesive foam and further stabilized by a crepe bandage around the head (2).…”

“…The interference from extracranial circulation on cerebral NIRS monitoring, particularly on classical Beer-Lambert (BL) parameters, was clearly evidenced during rather extreme maneuvers such as selective transient clamping of the external and internal carotid arteries in surgical patients (2,4). However, the contribution of extracerebral vascular beds to changes in putative intracerebral NIRS variables remains difficult to detect and quantify in physiological conditions and in response to standard hemodynamic tests.…”