| Question | Answer |
| BIS | "bispectral index" - noninvasive neurophysiologic monitoring device that continually analyzes pts EEG to assess the level of consciousness during anesthesia |
| EEG | 1. monitors cerebral fx & provides early evidence of cerebral ischemia
2. records stages of wakefulness and consciousness resulting from neurotransmitter activity |
| depth of anesthesia | likelihood of forming memory |
| bispectral analysis | bispectral index of an EEG = wt'd sum of EEG subparameters of time domain, frequency domain, higher order spectral info |
| how the BIS works | EEG that employs computerized algorithms to incorporate established EEG patterns into usable info |
| risk for awareness - high to low | 1. OB (GA is emergent ie 30 sec)
2. major trauma
3. CP bypass
4. physiologically most fragile (elderly)
5. multiple co-morbidities
6. ETOH/drug abusers |
| factors contributing to awareness | 1. polypharmaceutical approach to anesthetic
2. TIVA (gas gives better amnesia)
3. premature lightening for rapid turnover |
| steps to ↓ risk of awareness | 1. premedicate w/ amnestic drugs
2. give more than "sleep dose" of induction agents if followed immediately by intubation
3. avoid NMBDs unless absolutely necessary
4. periodic maintenance of machine/vaporizers
5. CHECK machine/vent prior to use |
| BIS = ZERO | EEG silence |
| BIS = 100 | expected value in fully awake adult |
| BIS = 40-60 | generally accepted level for GA (manufacturer claims never been recall case when documented BIS < 60) |
| BIS = 75-80 | pt can start to move |
| BIS changes with noxious stimuli | lack of analgesia (can be used to monitor lack of analgesia - lower drug utilization w/o ↑ somatic s/s of light anesthesia ie movement, hemodynamics) |
| when to place BIS | ideally before induction to establish baseline |
| BIS SQI | Signal Quality Index - quality of EEG 0-100
~want ↑↑ # ~not reliable if <80 |
| BIS EMG | Electromyograph - 30-55 - absolute power in 70-110 Hz frequency band (this freq. band contains power from muscle activity as well as high freq artifacts ~ want ↓↓ # ~ reasonably accurate BIS if < 25 |
| BIS SR | suppression ratio - indicates % of suppressed (flatline) EEG detected over last 63 sec |
| BIS smoothing rate | time period over which artifact-free data is analyzed to calculate the BIS #. affects trend & #. Factory default = 15 sec. 'smoother' trend with 30 sec. |
