ADVANCE: Assessment for Defining Variability in Anesthesia Through Novel Clinical EEG
Condition: Pain
Study type: Observational

Summary: 
      The present study is designed to compare prospectively whether sBIS, sEMG, or CVI variability
      (brain monitoring) can be used to predict unwanted intraoperative responses (high blood
      pressure, fast heart rate, tearing, etc.) to stimulation (pain) and to determine whether
      these intraoperative findings are related to patient-assessed postoperative pain scores.

      The hypothesis is that increases in these variability measures are associated with increased
      probability of unwanted responses. If confirmed, these variability measures may help
      anesthesia providers by highlighting periods of inadequate analgesia (pain relief).
    

Detailed description: 
      Anesthesia providers have been using processed EEG parameters (brain monitors) to assess the
      depth of anesthesia for many years. The Bispectral Index (BIS®; Aspect Medical Systems,
      Inc.), one such brain monitor, provides a direct measure of the hypnotic state of the patient
      [1, 2]. These clinicians use the BIS value, a number ranging from 0 (very deep anesthesia) to
      100 (awake state), to help optimize anesthetic dosing. Using BIS technology, anesthesia
      providers may adjust anesthesia doses to provide adequate sedation while avoiding over
      sedation, resulting in faster recovery [3] and a reduced incidence of awareness with recall
      [4].

      While BIS technology helps anesthesia providers achieve desired levels of hypnosis, they
      currently rely primarily on monitoring hemodynamic (blood pressure and heart rate), autonomic
      (tearing, sweating), and somatic (moving) responses to noxious (painful) stimulation as a
      means to detect potential patient arousals. Additional analgesics (narcotics, NSAIDS) are
      often administered in order to suppress further response to noxious (painful) stimulation.
      Several studies have shown that noxious stimulation can also affect EEG signals, resulting in
      increased variability in the BIS index, suggesting that information in EEG signals could
      potentially help clinicians anticipate and detect patient response to noxious stimulation.

      Ropcke et al. [5] showed that BIS values were higher with surgical stimulation than without
      any stimulation. Other reports have shown that focal noxious stimuli in volunteers and
      patients induce transient increases in BIS [6-9]. Many of these studies show that adding
      analgesics suppresses the BIS response to noxious stimulation, and the level of suppression
      achieved was related to the dose of the added drugs [6, 8, 9].

      Based on these findings, it is expected that insufficient analgesia would likely result in
      transient increases in BIS due to ongoing surgical stimulation, increasing the overall
      variability of BIS. Recently reported findings confirm that overall variability of BIS
      increased prior to and following intraoperative somatic events [10]. These reports also
      identified similar increases in variability of the EMG, with the largest changes realized
      from a Composite Variability Index (CVI) which combined the BIS variability (sBIS) and EMG
      variability (sEMG) into a single value. Other studies have also shown an association between
      these variability measures and postoperative pain scores [11, 12]. These studies showed that
      sBIS, sEMG, and CVI computed over the entire surgical procedure were all higher in both
      adults and children with worse postoperative pain scores. However, the reliability and
      optimum method of displaying these variability scores has yet to be been determined.

      The present study is designed to compare whether sBIS, sEMG, or CVI can be used to predict
      unwanted intraoperative somatic responses to stimulation, and to determine whether these
      values are related to patient-assessed postoperative pain scores. Our hypothesis is that
      increases in these variability measures are associated with increased probability of somatic
      responses. If our hypothesis is confirmed, these variability measures may help clinicians by
      highlighting periods of inadequate analgesia.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Patients, aged 18-80, under general anesthesia for a moderately painful elective surgical
        procedure.
      
Keywords: Analgesia; Bispectral Index; BIS Variability; Electroencephalography; Electromyography; Monitoring, Intraoperative; Movement; Pain, Postoperative; Somatic Events; Patients under general anesthesia undergoing a moderately painful procedure.