Relationship Between Bispectral Index, EEG Features, and Propofol Effect-site Concentration in Young and Elderly Patients.
Condition: Electroencephalography; Aging; Propofol; Depth of Anesthesia
Study type: Observational

Summary: 
      The aim of this study is to describe the BIS values and electroencephalographic patterns
      during total intravenous anesthesia with propofol-remifentanyl, in patients from 18 to 85
      years.
    

Detailed description: 
      Propofol is an anesthetic drug regularly used in elderly patients requiring anesthesia. The
      electroencephalographic pattern recognized when propofol is administered is different from
      the pattern obtained in younger patients. Both groups present alpha and slow delta bands, but
      younger patients present more intense electroencephalographic bands than older patients (1).
      The correlation between BIS values and the power of electroencephalographic frequency bands
      during propofol-remifentanyl anesthesia has not been determined.

      The investigators will describe the changes in BIS values and electroencephalographic
      patterns in young and elderly patients receiving propofol-remifentanyl anesthesia for
      elective surgery, at different propofol concentration levels. Formal characterization of the
      dynamic relationship between propofol concentrations at the effect site (Ce), spectral power,
      and BIS values may provide clinically relevant information to design propofol dose schemes in
      elderly patients.

      The investigators will carry out a prospective observational clinical study at the Clinical
      Hospital of the Catholic University of Chile. 30 patients, aged 18-85 years, scheduled to
      undergo elective surgery will be recruited. Standard monitoring and 2 frontal EEG monitors
      will be installed: Sedline® and BIS®. The electroencephalographic signal from these monitors
      will be recorded simultaneously from anesthesia induction until extubation. Propofol will be
      started at a rate of 15-20 mg/kg/hr in patients >65 years and 20-25 mg/kg/hr in younger
      patients (<65 years) until a suppression rate (SR) >1% appears in the BIS® EEG monitor. If
      the SR is not achieved, the infusion rate can be increased by 5 mg/kg/hr every 5 minutes
      until 25 mg/kg/hr in the elderly group and 30 mg/kg/hr in the younger group. When the SR
      appears, propofol infusion will be stopped. The induction phase will be considered completed
      at this point. Loss of response (LOR), defined as the timepoint when patients became
      unresponsive to verbal commands, soft shaking, and eyelash reflex, will be assessed every 30
      seconds. When patients become apneic, positive pressure mask ventilation will be started
      gently at a rate of 10 breaths per minute. After induction of anesthesia, opioids and
      neuromuscular blocking drugs will be given to facilitate tracheal intubation. When BIS values
      increase to recommended hypnotic levels for surgery (40-60), the propofol infusion rate will
      be started again at half of the induction rate. This rate will be adjusted to maintain the
      alpha band present in the Sedline spectrogram and SEF95 between 8-12 Hz. BIS monitor will be
      covered and hidden from the attending anesthesiologist during the maintenance phase. After
      surgery ends, EEG monitoring will continue until the patient's extubation. One hour after
      extubation, the Brice questionnaire will be performed to detect intraoperative awakening.
      Propofol concentration will be estimated using the Schnider model.
    

Intervention name(s): Propofol
Intervention type(s): Drug
Intervention description(s): Propofol will be started at a rate of 15-20 mg/kg/hr in patients >65 years and 20-25 mg/kg/hr in younger patients (<65 years) until a suppression rate (SR) is achieved. If not, can be increased by 5 mg/kg/hr every 5 minutes up to 25 mg/kg/hr in the elderly group and 30 mg/kg/hr in the younger group or after 15 minutes have passed. When the SR appears, propofol infusion will be stopped. Then restarted at half of the initial rate. Maintenance of anesthesia will be guided by Sedline Monitor to maintain an alpha band present in the spectrogram and SEF95 between 8-12 Hz. BIS monitor will be covered. Both EEG signals (Sedline and BIS) will be registered simultaneously until the patient's extubation.
Other intervention name(s): Diprivan; Propoven
Intervention MeSH terms: Propofol
Observational model: Cohort
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Elderly patients scheduled for surgery are an understudied population. Incidence of
        postoperative delirium and other complications can be related to changes in cerebral
        dynamics under anesthesia, with effects observed even after the use of anesthetics agents.

        Formal characterization of the dynamic relationship between propofol concentrations at the
        effect site (Ce), spectral power, and BIS values may provide clinically relevant
        information to design propofol dose schemes in young and elderly patients.
      
Keywords: electroencephalography; bispectral index; propofol; alpha band; aging; burst suppression