EEG Monitoring to Assess Emergence From Neuroanesthesia
Condition: Cerebral Aneurysm; Trigeminal Neuralgia
MeSH terms: Trigeminal Neuralgia; Neuralgia; Intracranial Aneurysm; Aneurysm
Study type: Interventional

Summary: 
      A highly desired result in neuroanesthesia is a prompt, controlled emergence following a
      neurosurgical procedure. Considerable strides have been made in this direction with volatile
      anesthetic agents such as sevoflurane or desflurane administered in association with the
      narcotic remifentanil. It is characteristic that patients will emerge within 5 to 10 minutes
      of cessation of these agents at the end of a neuroanesthetic. However, there are cases where
      emergence is delayed, especially after periods of deep anesthesia for i) cerebral protection
      with temporary clipping of cerebral aneurysms and ii) with microvascular decompression for
      trigeminal neuralgia. Deep levels of anesthesia are standard for these procedures in the
      posterior fossa, which utilize motor evoked potentials to assess cranial nerve function. In
      these cases, EEG monitoring is standard. Using the EEG to monitor emergence to aid its
      progress makes sense. A monitor which could predict emergence in these patients would be
      valuable. EEG monitoring engineered to provide this information is now available in the form
      of the EEGo. This study is designed to test the hypothesis that the EEGo monitor will be
      superior to the BIS monitor to assess emergence following neuroanesthesia.
    

Detailed description: 
      Objective: This study is designed to test the hypothesis that the EEGo monitor will be
      superior to the BIS monitor to assess emergence following neuroanesthesia. The EEGo will be
      able to more accurately indicate emergence and direct therapy at the end of the operative
      procedure. The EEGo will be superior because the raw EEG 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 from deep anesthesia to emergence. It is this transition that permits acute assessment
      of emergence. The ability to process the EEG and display phase delay plots in 50 msec is what
      makes the EEGo monitor attractive to acutely assess emergence from neuroanesthesia. Accurate
      emergence will allow better anesthesia management.

      This pilot study will be done to assess a nonlinear EEG monitor (EEGo) to direct therapy and
      predict prompt emergence from neuroanesthesia where EEG monitoring is done in neurosurgical
      cases. In our centre we routinely monitor the EEG, SSEP and/or MEP during temporary aneurysm
      clipping and during microvascular decompressive surgery. It is just these cases where
      emergence can be delayed despite following standard neuroanesthesia techniques. 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 3-D 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 therapy during anesthesia emergence, better predict
      emergence, facilitate extubation based on the awake state, allow titration of vasoactive
      agents during emergence to smooth hemodynamic control and permit more rapid emergence at end
      procedure. The EEGo will be compared directly in real time to the bispectral (BIS) monitor re
      goal directed emergence. If efficacy is shown with the EEGo, a more formal comparison to BIS
      and clinical judgement will be studied.

      BIS monitoring can aid emergence in outpatient procedures, both with time to wakening and
      time in the recovery room. These results also impact on the cost of anesthetic drugs and OR
      and Recovery Room costs. Work demonstrating accelerated emergence from desflurane with BIS do
      not highlight the manner in which the BIS directs the emergence. The depth of anesthesia is
      adjusted to 50 - 60 ABU during maintenance and then emergence is tracked. A specific BIS
      number to indicate emergence is not suggested. In fact, a correlation between the BIS in the
      awake state and with movement and eye opening appears poor with the emergence BIS usually
      being lower than the pre-induction BIS. The BIS may also on occasion be very low during
      emergence - deemed artifactually so and in this work it is suggested that the raw EEG be
      observed to aid emergence. It would seem that significant issues relate to intra and
      interpatient variability with this processed EEG signal. Recent work suggests significant
      discrepancy of BIS signals between hemispheres and even recording from two sites in the same
      hemisphere. In addition, BIS correlates poorly with end-tidal desflurane and awake state.

      Thus, it would seem that while the BIS can aid management of depth of anesthesia during
      maintenance, it is not ideally suited to direct a facilitated emergence. In contrast, the
      EEGo monitor uses nonlinear analysis techniques to provide a visual output related to depth
      of anesthesia.
    

Intervention name(s): On-line EEG monitoring during neurosurgery; EEGo vs BIS
Intervention type(s): Device; Device
Intervention description(s): Comparison of 2 ways of processing the EEG signal; comparison of two processed EEG monitors.
Other intervention name(s): EEGo; BIS Vista
Allocation: Randomized
Intervention model: Single Group Assignment
Masking: Triple (Participant, Care Provider, Investigator)
Primary purpose: Diagnostic