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Information

(see also ABCDE Bundle; Pain Management; Ramsay Scale; Richmond Scale; Riker Scale)

A processed EEG parameter used to measure the hypnotic effects of anesthetic and sedative agents on the brain. A sensor is placed on the patient's forehead, and the BIS monitor translates information from the EEG into a single number (i.e., 100 = wide awake; 0 = absence of brain activity). BIS data may also show signs of cerebral injury not evident on exam and provide early indication of poor outcome. Use of the BIS monitor does not replace the use of the peripheral nerve stimulator and may help objectively guide the sedation and analgesia for this patient. Either Riker Sedation-Agitation Scale or Richmond Agitation-Sedation Scale (RASS) is frequently used in conjunction with BIS monitoring to document the patient's level of sedation.

Electrode Placement

After wiping the forehead with alcohol and drying with gauze, position the electrodes. In most cases, either side can be used, but if the patient has had a stroke, place it on the unaffected side.

  • Place electrode #1 at the center of the forehead, about 1½ inches above the bridge of the nose.
  • Place electrode #4 directly above and adjacent to the eyebrow.
  • Place electrode #3 on the temple, between the outer canthus of the eye and hairline.
  • Electrode #2 will then be in proper position to be secured.

Monitoring

After connecting cable, each electrode needs to self-test and “pass” before monitoring can begin. Watch the signal quality index (SQI) bar for EEG activity.

Assessment

Table 1.4

Troubleshooting

  • Replace sensors every 24 hours. Perform a skin assessment when changing them.
  • When disconnecting sensor, press release button on interference cable.
  • Increased EEG activity may artificially increase BIS score; be sure to check SQI.
  • False BIS highs may also be due to the following:
    • High-frequency power contained in pacemakers, EKG signals, warming blankets, or oscillating ventilators
    • Muscle shivering, tightening, or patient motion
    • Neuromuscular blocking agents that may be wearing off
    • REM sleep
    • Pain
Key Point

During stable propofol anesthesia, small doses of ketamine (<0.2 mg/kg) will not increase BIS values. However, at higher doses (>0.5 mg/kg), increases may be noted.

  • BIS lows may be due to:
    • Neuromuscular blockade

Figure 1.10