Quantitative Electroencephalogram and Bispectral Index Brain Mapping During Propofol vs Sevoflurane General Anesthesia
Condition: Neurophysiology
Study type: Observational

Summary: 
      General anesthesia interferes with the whole cerebral cortex at different levels. The goal
      was to investigate the impact of general anesthesia on different regions of the cerebral
      cortex by recording the brain's electrophysiological activity using QEEG and BIS during
      general anesthesia for 40 patients undergoing orthopedic surgeries under general anesthesia
      to see whether our hypothesis, that there is a topographically-dependent impact of general
      anesthesia on different regions of the cerebral cortex, is valid or not. The patients were
      randomly divided into 2 groups of 20 patients to compare the effect on the brain function
      monitoring (QEEG vs BIS) of the intravenous anesthesia (propofol) with the halogenated
      anesthesia (sevoflurane). And finally, we compared the two brain function monitoring
      techniques, BIS and QEEG.
    

Detailed description: 
      After approval by the ethics committee, every patient signed a consent form to participate in
      this observational prospective open-label randomized study. We identified potential
      participants in the anesthesia pre-admission unit who presented to be seen by an
      anesthesiologist before their intervention. Details of eligibility criteria described later.

      According to the international 10-20 reference system, 4 silver cup electrodes were placed on
      the left prefrontal (Fp1), parietal (P7), temporal (T7), and occipital (O1) points with the
      vertex (Cz) as a common reference after an adequate preparation of each scalp skin location
      using a micro-abrasive paste and degreasing using ethyl ether. The cup electrodes were placed
      and fixed on the skin with adhesive paste . After a similar skin preparation, an adult
      adhesive EKG surface electrode was secured to the patient's forehead as a cephalic ground
      electrode. Thus, by using 6 electrodes, we obtain a 4 channels set-up (prefrontal Fp1-CZ,
      parietal P7-Cz, temporal T7-Cz, and occipital O1-Cz) with a common vertex reference.

      Each of the six electrodes of the montage are respectively connected to one special Y adapter
      including a double connection to be attached at the same time to the EEG amplifier, for the
      QEEG recording, and to the A1000™ Aspect Medical System™ amplifier, for the BIS recording.
      After the initial test of the electrode impedance (<5000 Ω), this last one was automatically
      checked all along the investigation to maintain the electrodes impedance below the same
      threshold. Regarding the QEEG, the low- and the high-frequency filters were set at 0.5 and 30
      Hertz (Hz), respectively. EEG five seconds long epochs were sampled every 30 seconds for
      further analysis in the three respective domains (frequency, time, and power) in each EEG
      channel. Concerning the BIS monitoring, the EEG low- and high-frequency filters were set
      similarly to the QEEG whereas EEG sampling corresponds to 5-second segments of traces without
      smoothing, every 30 seconds. Finally, the BIS and its ancillary parameters simultaneously
      calculated in each channel, were extracted every 30 seconds. The selection of parameters for
      the QEEG analysis included Spectral Edge Frequency (SEF), Median EEG Frequency (MEF), Burst
      Suppression Ratio (BSR) and Total Spectral Power (TSP). Regarding the bispectral EEG
      analysis, the only parameter was the BIS itself. Thus, each parameter value is obtained for
      each channel during EEG and BIS sampling. Finally, for clinical monitoring, heart rate (HR),
      mean arterial pressure (MAP) and pulse oximetry (Sa02) were considered.

      After the standard clinical monitoring placement (ECG, non-invasive arterial pressure cuff
      and ear/finger pulse oximetry device) and a peripheral venous catheter insertion connected to
      an infusion line, the non-premedicated patients were preoxygenated with a facial mask with
      100% oxygen. Capnography via nasal cannula were initially applied and monitored prior to the
      anesthetic induction and replaced by the manual ventilation system when needed during the
      general anesthesia (GA) effect occurrence. First, every patient received an intravenous (iv)
      bolus of 0,2 μg.kg-1 sufentanil. After that, in the group 1 the propofol (P) infusion was
      started using target-controlled infusion (TCI) with a Total IntraVenous Anesthesia (TIVA)
      pump (Schnider's pharmacokinetic/pharmacodynamic data set); targeting the
      effect-concentration of 3µg.ml-1. From then on, the effect concentration was gradually
      increased by 1µg.ml-1 every two to three minutes until loss of consciousness (LOC as loss of
      verbal contact, spontaneous ventilation, corneal reflex, and ciliary reflex) occurred. At
      this point the effect concentration level of propofol upon loss of consciousness (PROPLOC) is
      recorded. At the same time, in group 2, sevoflurane (S) is started at one minimal alveolar
      concentration (2% in 50% oxygen) during mask assisted ventilation. Then, in a similar manner
      to group 1, the S concentration is gradually incremented by 2% until the LOC when the mask
      ventilation became fully assisted. The corresponding S effect-concentration (SEVOLOC) was
      also noted. Subsequently, the LOC confirmed, after an interval of 1 to 2 minutes, a first
      laryngoscopy was performed to test the possibility of intubation of the patients. In case of
      adequate intubation conditions (no physical or hemodynamical reaction to laryngoscopy and/or
      normal airway compliance), 0.1 mg.kg-1 of iv cisatracurium was given to prepare definitive
      intubation. When the patients did not encounter correct intubation conditions (first
      laryngoscopy failure), the P effect-concentration and the S end-tidal concentration were
      respectively increased of 1µg.ml-1 and 1% until the test laryngoscope was successful. After
      intravenous cisatracurium administration, manually assisted ventilation was conducted for 3
      minutes in a way to have the partial pressure of end-tidal carbon dioxide (etCO2) between
      32-35 mmHg. Intubation followed and intermittent positive pressure ventilation was used
      maintaining the same values of etCO2. The corresponding drug concentrations of propofol at
      intubation (PROPIntub) and sevoflurane at intubation (SEVOIntub) were recorded. From the
      moment the patient is mechanically ventilated, the effect concentration of propofol and the
      end-tidal concentration of sevoflurane are reduced to 3 to 4 µg.ml-1 and one minimal alveolar
      concentration (MAC) respectively while awaiting the surgical incision. Then, during the
      following 15-minute period of data collection no external stimuli were permitted on or around
      the patient. This pharmacological steady-state period was considered for the comparative
      topographic analysis between the different electrode categories regarding the general
      anesthesia effect on the brain. Therefore, the intraoperative period extends from the
      surgical incision to the end of the surgery. During this period, it is left to the discretion
      of the anesthetist to add either an iv bolus of sufentanil (0.1 μg.kg-1) and/or an iv bolus
      of cisatracurium (0.1 mg.kg-1) only if necessary, in the clinical judgment of the
      practitioner. To note, the parametric values of the QEEG and BIS were not considered to guide
      the anesthesia throughout the investigation. The postoperative period begins after the end of
      surgery when the anesthesia is stopped and lasts until the patient is awake and calm, ready
      to leave the operating room after extubation.
    

Intervention name(s): Propofol 1 % Injectable Suspension; Sevoflurane inhalant product
Intervention type(s): Drug; Drug
Intervention description(s): Induction and maintenance of general anesthesia using the intravenous anesthetic; Induction and maintenance of general anesthesia using the inhaled anesthetic sevoflurane
Other intervention name(s): Diprivan; Sevorane
Intervention MeSH terms: Propofol; Sevoflurane
Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        Patients scheduled for an orthopedic surgery to be operated in Erasme hospital, Belgium
      
Keywords: General anesthetics; Bispectral index; Quantitative electroencephalography; Monitoring