Comparison Of Noninvasive Cerebral Oxygen Saturation Monitoring With Somatosensory Evoked Potential Monitoring In Carotid Endarterectomy

【Objective】Through prospective paired design,each subject was monitored for Somatosensory Evoked Potential（SSEP）and NIRS-based（Regional cerebral oxygen saturation,rSO₂）monitoring during endarterectomy（CEA）.The optimal intervention threshold of rSO₂ was to be calculated,and the correlation between rSO₂ monitoring and SSEP during CEA was to be observed.The role of dual-channel NIRS based rSO₂ monitoring in CEA surgery was to evaluate.【Methods】Sixty-three patients subjected to elective carotid endarterectomy were selected,fifty-eight of whom were ASA grade I-III,age 55-82 years old.Five patients underwent bilateral CEA and fifty-three patients underwent unilateral CEA.Through paired design,SSEP and NIRS monitoring were performed during the operation for each subject.The SSEP monitoring before blocking was used as the basic value of SSEP monitoring.After blocking,the SSEP monitoring amplitude decreased by≥50%was set as positive result.The minimum value of rSO₂ after blocking,and the average rSO₂ value 5 minutes before blocking,5 minutes after blocking,and 5 minutes after reopen was recorded respectively.The SSEP monitoring was used as judgement to form an ROC curve.After finding the optimal threshold for rSO₂ monitoring intervention from the ROC curve,the consistency and correlation between r SO₂monitoring and SSEP monitoring were obtained.【Results】Sixty-three operations,successfully completed in fifty-eight patients with positive SSEP monitoring observed in eight patients during the operation,and shunts were performed in two patients.According to the ROC curve,the optimal intervention threshold was defined as a decrease of 9.48%of rSO₂ comparing to the baseline and/or an absolute decrease of 6.22 of rSO₂ value.The comparison of the intervention threshold of rSO₂ and SSEP monitoring showed that the consistency of the prediction of cerebral ischemia was general（Kappa=0.491,P<0.001）.The overall detection rates of the two monitoring methods were different,and the difference was statistically significant（χ2=12.954,P<0.001）.During CEA surgery the sensitivity of rSO₂monitoring was 75%（95%CI:5.58%～95.55%）,the specificity was 87.27%（95%CI:74.90%～94.31%）,and the positive predictive value was 46.15%（95%CI:20.40%～73.88%）,the negative predictive value was 96%（95%CI:85.14%～99.30%）,and the accuracy was 85.71%.【Conclusion】In this study,compared to SSEP monitoring,a decreased of 9.48%of rSO₂ and/or an absolute decreased value of rSO₂>6.22 was defined as the intervention threshold.The sensitivity and the positive prediction value of rSO₂ monitoring were low,indicating that when the above threshold was used,some positive patients may not be diagnosed,and some patients may receive unnecessary intervention.Therefore,according to this study,using rSO₂monitoring alone to predict intraoperative ischemia in CEA patients was not supported.However,rSO₂ monitoring was superior to SSEP monitoring in reflecting blood flow changes in CEA,and it may have a guiding role for intraoperative head positioning.