EEG, Cerebral Oximetry, and Arterial to Jugular Venous Lactate to Assess Cerebral Ischemia During Carotid Endarterectomy
Condition: Internal Carotid Artery Stenosis
MeSH terms: Brain Ischemia; Cerebral Infarction; Carotid Stenosis; Ischemia
Study type: Interventional

Summary: 
      A highly desired result during carotid endarterectomy (CEA) is the ability to predict and
      warn the surgeon if the brain is at risk of damage during the period of time that the carotid
      artery is cross-clamped for surgical repair of the vessel narrowing. A number of approaches
      for cerebral monitoring have been developed, including EEG, cerebral oximetry, and
      measurement of arterial to jugular venous concentration differences of oxygen, glucose or
      lactate. This study will utilize and compare multiple monitoring approaches for detecting
      when and if the brain is at risk of injury during CEA. As such, this robust approach to
      monitoring may permit a more prompt intervention to prevent or limit damage should cerebral
      ischemia occur. In this study we will compare a processed EEG monitor -- the EEGo, which uses
      nonlinear analysis to a bispectral (BIS) index monitor, and to the FORE-SIGHT cerebral
      oximeter to assess the ability of each to identify cerebral ischemia should it occur with
      carotid artery cross-clamping during CEA. These monitors will be correlated with arterial to
      jugular venous lactate concentration difference, which has recently been shown to be a
      sensitive indicator of hemispheric ischemia during CEA.
    

Detailed description: 
      Objective: This study is designed to test the hypothesis that the EEGo monitor will be
      superior to the BIS monitor to assess onset of cerebral ischemia if it should arise during
      CEA. The two EEG monitors will be compared with the FORE-SIGHT cerebral oximeter, and all
      three monitors will be correlated with arterial to jugular venous lactate differences before,
      during and after carotid cross-clamping.

      We hypothesize that the EEGo monitor will be able to more accurately indicate if the brain is
      at risk of ischemia and better able to direct therapy to relieve the ischemic episode as
      compared to the BIS monitor. The EEGo will be superior because the raw signal is processed
      using phase delay analysis, with each patient's raw EEG analyzed instead of a proprietary but
      generic signal processing approach on a linear scale as with the BIS monitor. Phase delay
      analysis is a standard approach to display nonlinear signals. A highly reproducible signal
      transition occurs with differing depths of anesthesia. The ability to process the EEG and
      display phase delay plots in 50 msec is what makes the EEGo monitor attractive to acutely
      assess changes in the EEG which can manifest with cerebral ischemia. We also hypothesize that
      the FORE-SIGHT cerebral oximeter will be an effective monitor for detecting cerebral ischemia
      during CEA. Accurate assessment of changes in the EEG and cerebral tissue oxygen saturation
      with carotid cross-clamping will allow better anesthesia management of patients undergoing
      CEA.

      This pilot study will be done to assess the ability of the nonlinear EEG monitor (the EEGo)
      compared to the BIS monitor and the FORE-SIGHT cerebral oximeter to direct therapy if
      cerebral ischemia occurs -- notifying the surgeon of the findings, optimizing the blood
      pressure, arterial oxygenation and carbon dioxide tensions, and permitting consideration of
      placing a carotid shunt. The EEGo processes the standard EEG signal by nonlinear analysis of
      the raw signal by 3 dimensional phase delay plots. A cascade from a point attractor, periodic
      attractor, toroidal attractor to a 3D chaotic attractor occurs from burst suppression to the
      awake state. These resemble phase transitions and occur rapidly from one state to the next.
      An analogy is the phase transition that occurs when water changes to ice and vice versa.
      Monitoring these transitions should permit a rational approach to monitoring cerebral
      well-being during carotid cross-clamping with CEA. The EEGo will be compared directly in real
      time to the bispectral (BIS) monitor and to the FORE-SIGHT cerebral oximeter for
      intraoperative monitoring during CEA.

      Cerebral oximetry (also known as Near Infrared Spectroscopy or NIRS) provides a non-invasive
      measure of regional cerebral tissue oxygen saturation which reflects local oxygen supply and
      demand, and could indicate cerebral ischemia when desaturation occurs. The FORE-SIGHT
      cerebral oximeter is a non-invasive, optically-based near-infrared spectrometer that
      continuously estimates absolute cerebral tissue oxygen saturation, and works based on the
      principal that hemoglobin's two forms -- oxygenated and deoxygenated -- absorb light
      differently. The sensor projects laser into the brain at four different wavelengths (to
      maximize accuracy), with the reflected light being analyzed via algorithm to an absolute
      value of cerebral saturation. The FORE-SIGHT has been validated in several studies that have
      shown good precision of the cerebral tissue oxygen saturation value.

      In addition, as previously stated, the two EEG monitors and FORE-SIGHT cerebral oximeter will
      be correlated with arterial to jugular venous lactate differences. In a recent paper,
      arterial to jugular venous lactate differences were shown to be especially sensitive for
      detecting cerebral ischemia in awake surgery for CEA. In that paper the sensitivity of
      lactate differences to detect ischemic changes was 100% for a difference greater than 0.1
      mmole/L; 100% specificity if the difference exceeded 0.32 mmole/L; and an ROC best fit for a
      difference greater than 0.16 mmole/L. In this study we plan to look at a combined approach
      during carotid artery cross-clamping -- measures of lactate differences with simultaneous
      assessment of cerebral tissue oxygen saturation using the FORE-SIGHT cerebral oximeter, and
      EEG changes using two different processed EEG monitors (the well established BIS monitor and
      the newer EEGo monitor). As such, this is intensified monitoring for these patients at risk
      of cerebral ischemia over the standard of care.
    

Intervention name(s): EEGo, BIS, FORE-SIGHT cerebral oximeter
Intervention type(s): Device
Intervention description(s): The EEGo monitor, BIS monitor, and FORE-SIGHT cerebral oximeter will be used for cerebral monitoring of all patients. A comparison of the three monitors will be done. For EEGo monitoring, five bipolar electrodes will be placed per International 1020 system. For BIS monitoring, the BIS quattro sensor will be placed on the forehead in usual fashion. For FORE-SIGHT monitoring, the two sensor strips will be placed on the forehead in usual fashion.
All patients will have their ipsilateral Internal Jugular vein cannulated by the surgeon intraoperatively with a 16g IV cannula, through which a Portex multi-orifice epidural catheter will then be placed.
Other intervention name(s): BIS Vista monitor with BIS Quattro sensor; FORE-SIGHT cerebral oximeter
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: Carotid stenosis; EEGo; nonlinear EEG; BIS; cerebral oximetry; FORE-SIGHT cerebral oximeter; cerebral monitoring; arterial jugular venous lactate difference; cerebral ischemia; carotid endarterectomy