Clinical validity of cerebral oxygen saturation measured by time-resolved spectroscopy during carotid endarterectomy

Background: Near-infrared spectroscopy has been used clinically to continuously and noninvasively monitor cerebral oxygen saturation (ScO2). However, there is no gold standard for measuring absolute values of ScO2. Although time-resolved spectroscopy (TRS) is one of the most reliable algorithms that reliably calculate absolute values of ScO2, there are very few clinical studies available. To evaluate the clinical relevance of ScO2 measurements using TRS, we compared ScO2 with jugular venous oxygen saturation (SjO2) during carotid endarterectomy. We also investigated factors associated with cerebral oxygen desaturation during clamping of the carotid artery. Methods: Sixty patients who underwent carotid endarterectomy were enrolled. ScO2 was measured by TRS-20 using TRS at 10 minutes before and after clamping of the carotid artery and 10 minutes after unclamping. SjO2 was measured simultaneously. The relationship between ScO2, SjO2, and estimated ScO2 (0.75×SjO2+0. 25×SaO2) were examined by simple regression and the Bland-Altman analysis. Factors related to ScO2<60% were investigated by logistic regression analysis. Results: There was a significant correlation between ScO2 and SjO2 (r=0.49, P<0.002). Bland-Altman analysis revealed narrow limits of agreement between ScO2 and SjO2 (bias, 9.2%; precision, 12.6%), as well as ScO2 and estimated ScO2 (bias,-1.3%; precision, 9.7%). Impaired cerebral hemodynamics (Powers stage 2 or Kuroda type 3) was significantly associated with ScO2<60%. Conclusions: ScO2 measured by TRS and SjO2 showed narrow limits of agreement. Reduced ScO2 was significantly associated with impaired cerebral hemodynamics.