BIS Monitor

Tenesma · Mar 15, 2003

yoga... yet again i am confounded by your statement: watches the patient and not hypnotized by monitors!!! i don't mean to pick a fight here, but i find it somewhat confusing...

first of all there are many situations where you can't watch your patient and all you have are monitors - what do you do then?

and those monitors are there for a reason: in fact it HAS become a legal issue as the ASA requires certain parameters to be monitored during the case. I don't recall any boxes on my anesthesia sheet that refer to "how does the patient look?"

you may have been practicing anesthesia for a while, and you may feel very comfortable with the level of anesthesia/the difficulty of patient/etc... from a legal point of view you are still held to the standard of care, and that standard of care is definitely evolving based on new graduates from CRNA/MD programs using new techniques/new equipment, further research, etc... that is why in order to maintain certification we have to take CMEs and take our board exams every so often. Just because you were in an awareness case that was won by the anesthesia provider based on patient misrepresentation doesnt mean anything at all....

i definitely don't think monitors are the end all - especially since most people don't even know how to interpret the data they see on those monitors - more than enough times i have seen a low saturation displayed on the screen and the anesthesia provider i was with was focusing on readjusting the pulseox on the finger - instead of listening to the lung sounds, etc..

but trust me, those monitors are your friends, will keep your patient safe and will keep you from writing bigger premium checks to your malpractice insurance company - and over time we will be developing new drugs/new equipment/new padding/new everything that will soon become the standard of care... and i am fully convinced that the BIS or some future generation of it will become a legal requirement for documentation on the chart - just like the oxygen saturation became a requirement in the 70s...

Passin' Gas · Mar 15, 2003

Great tool to help, not an end all to monitor anesthetic depth.

The bispectral index monitor can be indicative of level of consciousness and recall. Another important part of an anesthetic is preventing hemodynamic response to surgical stimulation. The BIS monitor does not reliably monitor these responses.

Monitor the patient, not the monitors

Tenesma, you hit on several things I believe should be remembered when discussing the BIS monitor.

1. We need to understand how the various monitors actually work; how does the monitor obtain the information it is displaying, what are the limitations of a particular monitor, what are factors that can interfere with proper function, etc.

The BIS is indicative of LOC and recall, this is only one part of the anesthetic state. Another important part of an anesthetic state is preventing hemodynamic response or movement in response to surgical stimulation. Just because the BIS reads 48, that does not mean (assuming no muscle relaxants are used) the patient won't move to surgical stimulation. Other parameters e.g. respiratory rate, depth, and pattern, HR, BP, etc. also provide information regarding depth of anesthesia.

2. The BIS monitor still has some significant limitations. However, as you pointed out, the technology is improving and it will more than likely be a standard monitor for a general anesthetic as is pulse oximetry, oxygen analyzer, end-tidal gas monitoring, etc.

3. Monitor the patient, not the monitors relates to the first point. It refers to acknowledging that these machines can malfunction, pulse oximeters get dislodged during positioning, VTach can show up on the ECG when the circulator is prepping the patient's chest, the arterial waveform can be dampened by a surgeon's or scrub tech's belly pressing on the wrist. Don't immediately give a vasopressor for a BP 64/52 when two seconds ago it was 102/52...the surgeon just stepped up to the table to harvest the graft from the leg and he/she doesn't shop in petites! You alluded to this same point with the low oxygen saturation, readjusting the probe rather than auscultating breath sounds.

4. Last year when we started to use the BIS monitors, the most interesting observation for me was that I did not change my anesthetic practice. I used the same end-tidal anesthetic concentrations and woke the patients up quickly, just as I had without the monitor.

For now, I use it on selected cases. In the future, it will probably be on the preprinted forms right under oxygen saturation, or more likely, automatically recorded by the computer along with the rest of the vital signs.

yoga crna · Mar 16, 2003

This has been a good discussion and hopefully has made us all look at our clinical practice. I will continue to closely monitor my patients, will probably not purchase a BIS monitor (I am in private practice and either purchase or have to strongly justify the purchase) of all anesthesia equipment) and continue to believe that my senses are the best monitors I have.

One final point, just yesterday I had the opportunity to see another anesthesia provider give anesthesia--I work alone, so this is an unusual occurence. That person was doing a crossword puzzle and not watching the patient or the monitors. We still have a long way to go.

Yoga

Brenna's Dad · Mar 18, 2003

The low down we are getting on the BIS monitor, is that it is a potentially useful tool, but still has a long way to go. Several individuals in my class have stories about getting a BIS reading of 40 on an orange, etc.

But then again, I am a total newb to anesthesia and have no personal experience using the BIS.

Tenesma · Mar 18, 2003

you will see electrical activity in an orange... but the BIS wouldn't interpret it as 40.... that isn't how BIS works :) it is basically monitoring two different types of brainwaves (based on frequency).

smiling_ru · Mar 19, 2003

I have had awake patients with a BIS of 50 and anesthetized patients with a bis of 90. It seems that sometimes the thing is somewhat accurate while at others it is useless. The technology does seem better then it used to be though. We trialed it in the ICU several years ago (before I went to anesthesia school) It was totally unreliable in that setting at that time.

I don't know, I tend to believe that it might give you a reading if it is attached to an orange. Maybe we should try it.

Tenesma · Mar 19, 2003

when you look at the literature for BIS use - its software algorithms only to be useful in situations where inhalational agents/propofol are used and not so much for other methods (ie: nitrous/narcotic) - in fact nitrous can sometimes spike the BIS higher... i definitely believe that it doesn't play a role in the ICU since mainly benzo/narcotis are used for sedation in that environment, and hence the BIS will be useless.

the more u use it the more of a feel you will get for how to use it.

i like to run my patients light, and with the BIS i can run them just light enough to avoid awareness and have very quick wakeups (including on isoflurane)