During use BIS was higher than expected. Why?
Interpreting BIS – BIS increases suddenly or is higher than expected
Clinical Situations that may indicate the need to increase anesthetic agents:
- Is there an increase in stimulation? When was an analgesic last given?
Adequate dosing for steady-state surgical maintenance may not be sufficient for increase in stimulation. - Has the anesthetic been decreased?Is the anesthetic dose sufficient?
Due to interpatient variability, some patients require higher doses of agents than others. - Are anesthetic delivery systems operating properly?
Check patency/integrity of IV lines and status of vaporizers.
EMG and high frequency artifacts that may falsely elevate the BIS:
- Is there any muscle shivering, tightening, or twitching?
The BIS value may be higher than the actual hypnotic state due to the presence of EMG. Check EMG bar for presence of EMG. - Did the patient receive any neuromuscular blocking agents that may be wearing off?
Check nerve stimulator for current state of muscle relaxation. Note: Facial muscles will recover sooner than skeletal muscles. - Does the patient have a pacemaker?
Check EEG waveform for presence of pacemaker or EKG spikes. - Has the use of any mechanical device that could generate high frequency activity (e.g. patient warmer) have been initiated or is any such device in close proximity to the BIS sensor?
Artifacts in the higher frequency ranges can artificially increase the BIS value. Check EMG bar for presence of high frequency artifacts. If possible move offending device away from BIS sensor.
Note: When these artifacts are present, the BIS should be interpreted with caution.
Source: BIS hanging cards, P/N 194-0066 Rev. 3.00
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