more BIS controversy

[Monty Python]

The BIS controversy continues:

Anesthesia Awareness and the Bispectral Index

Michael S. Avidan, M.B., B.Ch., Lini Zhang, M.D., Beth A. Burnside, B.A., Kevin J. Finkel, M.D., Adam C. Searleman, B.S., Jacqueline A. Selvidge, B.S., Leif Saager, M.D., Michelle S. Turner, B.S., Srikar Rao, B.A., Michael Bottros, M.D., Charles Hantler, M.D., Eric Jacobsohn, M.B., Ch.B., and Alex S. Evers, M.D



ABSTRACT

Background Awareness during anesthesia is a serious complication with potential long-term psychological consequences. Use of the bispectral index (BIS), developed from a processed electroencephalogram, has been reported to decrease the incidence of anesthesia awareness when the BIS value is maintained below 60. In this trial, we sought to determine whether a BIS-based protocol is better than a protocol based on a measurement of end-tidal anesthetic gas (ETAG) for decreasing anesthesia awareness in patients at high risk for this complication.

Methods We randomly assigned 2000 patients to BIS-guided anesthesia (target BIS range, 40 to 60) or ETAG-guided anesthesia (target ETAG range, 0.7 to 1.3 minimum alveolar concentration [MAC]). Postoperatively, patients were assessed for anesthesia awareness at three intervals (0 to 24 hours, 24 to 72 hours, and 30 days after extubation).

Results We assessed 967 and 974 patients from the BIS and ETAG groups, respectively. Two cases of definite anesthesia awareness occurred in each group (absolute difference, 0%; 95% confidence interval [CI], –0.56 to 0.57%). The BIS value was greater than 60 in one case of definite anesthesia awareness, and the ETAG concentrations were less than 0.7 MAC in three cases. For all patients, the mean (±SD) time-averaged ETAG concentration was 0.81±0.25 MAC in the BIS group and 0.82±0.23 MAC in the ETAG group (P=0.10; 95% CI for the difference between the BIS and ETAG groups, –0.04 to 0.01 MAC).

Conclusions We did not reproduce the results of previous studies that reported a lower incidence of anesthesia awareness with BIS monitoring, and the use of the BIS protocol was not associated with reduced administration of volatile anesthetic gases. Anesthesia awareness occurred even when BIS values and ETAG concentrations were within the target ranges. Our findings do not support routine BIS monitoring as part of standard practice. (ClinicalTrials.gov number, NCT00281489 [ClinicalTrials.gov] .)


Source Information

From the Department of Anesthesiology, Washington University School of Medicine, St. Louis.

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[Bertelman]

Is this published?

 

[coprolalia]

Interesting.

-copro

 

[Fastrach]

This study came out 2 months ago in NEJM, Mar 13, 2008.

http://content.nejm.org/cgi/content/short/358/11/1097?query=nextarrow

 

[cchoukal]

I'm not sure how reliable this study is in light of their sample size. Sure, they did a power analysis, but with an expected frequency of 1 in 1000, it's not suprising they didn't find a difference in frequency with group sizes < 1000.

 

[Planktonmd]

This study caused major trouble for Aspect.
It basically confirmed that most of the biased literature that Aspect used previously to push their product down our throats was just paid advertisement.
This doesn't mean that their monitor is completely useless but it just highlights that it's just another instrument that could be helpful in certain situations and when used by qualified people who understand it's limitations.

The BIS controversy continues:

Anesthesia Awareness and the Bispectral Index

Michael S. Avidan, M.B., B.Ch., Lini Zhang, M.D., Beth A. Burnside, B.A., Kevin J. Finkel, M.D., Adam C. Searleman, B.S., Jacqueline A. Selvidge, B.S., Leif Saager, M.D., Michelle S. Turner, B.S., Srikar Rao, B.A., Michael Bottros, M.D., Charles Hantler, M.D., Eric Jacobsohn, M.B., Ch.B., and Alex S. Evers, M.D



ABSTRACT

Background Awareness during anesthesia is a serious complication with potential long-term psychological consequences. Use of the bispectral index (BIS), developed from a processed electroencephalogram, has been reported to decrease the incidence of anesthesia awareness when the BIS value is maintained below 60. In this trial, we sought to determine whether a BIS-based protocol is better than a protocol based on a measurement of end-tidal anesthetic gas (ETAG) for decreasing anesthesia awareness in patients at high risk for this complication.

Methods We randomly assigned 2000 patients to BIS-guided anesthesia (target BIS range, 40 to 60) or ETAG-guided anesthesia (target ETAG range, 0.7 to 1.3 minimum alveolar concentration [MAC]). Postoperatively, patients were assessed for anesthesia awareness at three intervals (0 to 24 hours, 24 to 72 hours, and 30 days after extubation).

Results We assessed 967 and 974 patients from the BIS and ETAG groups, respectively. Two cases of definite anesthesia awareness occurred in each group (absolute difference, 0%; 95% confidence interval [CI], &#8211;0.56 to 0.57%). The BIS value was greater than 60 in one case of definite anesthesia awareness, and the ETAG concentrations were less than 0.7 MAC in three cases. For all patients, the mean (&#177;SD) time-averaged ETAG concentration was 0.81&#177;0.25 MAC in the BIS group and 0.82&#177;0.23 MAC in the ETAG group (P=0.10; 95% CI for the difference between the BIS and ETAG groups, &#8211;0.04 to 0.01 MAC).

Conclusions We did not reproduce the results of previous studies that reported a lower incidence of anesthesia awareness with BIS monitoring, and the use of the BIS protocol was not associated with reduced administration of volatile anesthetic gases. Anesthesia awareness occurred even when BIS values and ETAG concentrations were within the target ranges. Our findings do not support routine BIS monitoring as part of standard practice. (ClinicalTrials.gov number, NCT00281489 [ClinicalTrials.gov] .)


Source Information

From the Department of Anesthesiology, Washington University School of Medicine, St. Louis.

 

[brains]

That's very interesting. I just watched that movie Awake. It was a relatively good show, however, I didn't like how they made the anesthesiologist seem like a drunk fool at first.

 

[bostonblaz]

i am new to using bis as my home instatution didn't even have one but now i am somewhere that has one in every room. i wanted to know how people who use it regularly are using it. i just slap it on for s**** and giggles and i find most of my cases people are in the high 30's to high 40's, i am assuming i am runing them too deep. do you guys aim for the 50's?

 

[Monty Python]

i am new to using bis as my home instatution didn't even have one but now i am somewhere that has one in every room. i wanted to know how people who use it regularly are using it. i just slap it on for s**** and giggles and i find most of my cases people are in the high 30's to high 40's, i am assuming i am runing them too deep. do you guys aim for the 50's?

I personally think the BIS is a bunch of relative BS, although I give Aspect high marks for their pushy, scare-the-public, overboard marketing tactics.

Case in point: last week a surgeon bagged the innominate vein and knicked the aorta on a CABG re-do. (When he told me to drop the lungs I diplomatically inquired "are you sure - on a redo?" and he said yep. And he proceeded to saw right through those structures, adhered to the back of the sternum). Anywho ... he took 15 minutes to get on emergency bypass via the femoral structures ('cause those catheters weren't in the room), which was about 14 minutes after I packed the pt's head in ice (and called for pentothal which wasn't available ).

During the ensuing FIVE HOUR bypass run we got the pt's core temp to 18 degrees C. I still got BIS readings in the 60s.

To answer the questions:

Six liters of cell saver returned to pt, along with 8 units PRBCs, tons of FFP and platelets, etc. Took three separate administrations of protamine (total 750 mg) to get the ACT below 150. Pt was still intubated on POD 12 and got a trach. Neuro consult / CT brain / MRI = global hypoxic encephalopathy. Unfortunately that's no surprise; for about 10 minutes before going on bypass my ETCO2 was zero despite ventilating. We were shouting at the surgeon (note: singular surgeon) to start chest compressions but he was fixated on the femoral anatomy.

I guess one could argue that you don't do compressions on someone with a knicked aorta and transected great vein.

 

[milrisome]

I rarely use BIS. A few exceptions: hearts, TIVA, trauma. Occasionally when I am worried for some other reason, like a history of awareness or redheads. Maybe someone unstable so I can minimize anesthetic. Sounds like I should use it even less!

 

[dhb]

A lot of attendings like to slap the BIS on very few actually change their anesthetic in reaction to the reading: if the patient has a mac of agent and the BIS is 60 they don't crank up the gases and if the patient has an epidural and i'm running him on half mac with a BIS of 45 they'll come turn the dials saying half mac isn't enough

BIS = POS except it can sometimes give some confidence to go lower on the vapor on fragile patients.

 

[coprolalia]

BiS, for me, is only useful in two circumstances:

(1) Running a TIVA without neuromonitoring.

(2) Total circ arrest in bypass cases. Like to see that number hit "0" (or close to it).

-copro

 

[Dinkyconductor]

I did a neuro case last year with a BIS...

BIS never dropped below 90 the whole case. The patient had neuromonitoring for the case...EEG showed burst suppression. We were on something like 150 mcg/kg/min of propofol plus 3% des or so.

No, she did not have recall, despite what the BIS may have suggested.

 

[dfk]

BIS = attorney driven

 

[Planktonmd]

BIS = attorney driven

It was, but not after that study.

 

[amyl]

at the risk of sounding stupid: what does a BIS of zero mean? I know the formula is super secret but does a BIS of zero have any significance? i came across a case as a med student where the resident would have been better served by paying some more attention to the BIS. the BIS hit zero and was generally low and the patient kept having high peak airway pressures...she pimped me on the causes of high peak airway pressures and high end tidal CO2, which we ran through with no improvement...but lightening her up solved the problem completely... most attendings wouldn't have needed the BIS to tell them this i guess...
while i agree it shouldn't run the case but it can be a helpful number in light of the other numbers/clinical presentation.

 

[dfk]

at the risk of sounding stupid: what does a BIS of zero mean? I know the formula is super secret but does a BIS of zero have any significance? i came across a case as a med student where the resident would have been better served by paying some more attention to the BIS. the BIS hit zero and was generally low and the patient kept having high peak airway pressures...she pimped me on the causes of high peak airway pressures and high end tidal CO2, which we ran through with no improvement...but lightening her up solved the problem completely... most attendings wouldn't have needed the BIS to tell them this i guess...
while i agree it shouldn't run the case but it can be a helpful number in light of the other numbers/clinical presentation.

well, from my understanding and experience, a BIS of zero can signify: malfunction or supposedly way to deep of anesthetic, leading to toxicity.

 

[Magnus67]

at the risk of sounding stupid: what does a BIS of zero mean? I know the formula is super secret but does a BIS of zero have any significance? i came across a case as a med student where the resident would have been better served by paying some more attention to the BIS. the BIS hit zero and was generally low and the patient kept having high peak airway pressures...she pimped me on the causes of high peak airway pressures and high end tidal CO2, which we ran through with no improvement...but lightening her up solved the problem completely... most attendings wouldn't have needed the BIS to tell them this i guess...
while i agree it shouldn't run the case but it can be a helpful number in light of the other numbers/clinical presentation.

In my experience a BIS of zero means, a head CT with no grey/white matter differentiation, and withdrawal of care at 72hrs (therapeutic hypothermia protocol)

 

[Planktonmd]

at the risk of sounding stupid: what does a BIS of zero mean? I know the formula is super secret but does a BIS of zero have any significance? i came across a case as a med student where the resident would have been better served by paying some more attention to the BIS. the BIS hit zero and was generally low and the patient kept having high peak airway pressures...she pimped me on the causes of high peak airway pressures and high end tidal CO2, which we ran through with no improvement...but lightening her up solved the problem completely... most attendings wouldn't have needed the BIS to tell them this i guess...
while i agree it shouldn't run the case but it can be a helpful number in light of the other numbers/clinical presentation.

BIS = 0 is meaningless although the company says that it signifies toxic levels of anesthesia.
It means that you are beyond burst suppression in the depth of your anesthetic and basically beyond any clinically desirable anesthetic level.
I am not aware of any mechanism by which a low BIS number would indicate or cause high PIP.

 

[Sevo]

Is this published?

On the day it was released, Aspect's stock dropped 40%.

 

[SleepIsGood]

BIS = 0 is meaningless although the company says that it signifies toxic levels of anesthesia.
It means that you are beyond burst suppression in the depth of your anesthetic and basically beyond any clinically desirable anesthetic level.
I am not aware of any mechanism by which a low BIS number would indicate or cause high PIP.

When I use the BIS I try settng up the EEG mode on the screen. That way I can see the EEG tracing and can actually see Burst Suppression when it occurs (especially for neuro cases)....

So for me, it's not about the number solely. I like having it just as another tool. As someone mentioned earlier, it's also great when you are running TIVA. I guess during TIVA it acts as a sort of clutch.

 

[amyl]

she was fine when she woke up so i would go with BIS of zero not necessarily meaning toxic levels. she was definately too deep though...would that cause high etCO2 or high peak airway pressures? i know high flow can cause high peak airway pressures but i don't recall the flow rates being abnormally high.

 

[Planktonmd]

she was fine when she woke up so i would go with BIS of zero not necessarily meaning toxic levels. she was definately too deep though...would that cause high etCO2 or high peak airway pressures?
.

No

I know high flow can cause high peak airway pressures but i don't recall the flow rates being abnormally high.

Fresh gas flow and the concentration of inhaled anesthetics are 2 separate things and neither one has anything to do with the phenomenon that you mentioned ( Increased PIP in a patient with a BIS = 0).
There are a few concepts in anesthesia that you don't understand yet, but you soon will.

 

[amyl]

there are MANY MANY concepts in anesthesiology that I don't understand yet ;-)
but...
i have to survive the purgatory of intern year before i get to figure all this stuff out ;-(