How good is BIS? Does it prevent awareness?

OK, for those of you who are not practicing Anaesthetics this might be a bit boring, but it is an intriguing look at the way an idea can become entrenched in the medical psyche, even if the evidence doesn’t really support it.

BIS (electroencephalogram-derived bispectral index) is a monitor, applied usually to the patient’s forehead which measures a combination of EEG and EMG waves and gives a neat number between 0 and 100 (0 = no EEG activity, 100 = wide awake).  In theory we aim to run the patient between 40 and 60 in order to ensure no awareness occurs during anaesthesia.

BIS and its analogues are becoming standards of care in many hospitals.  In my practice I only use them in scenarios where I feel there is an increased risk of awareness, or in the cases where the patient has specific concerns or previous experience of operative awareness.  What is your practice with regards to BIS monitoring?

There is some evidence that shows the use of BIS detects awareness –

This Scandinavian study was a prospective – historical controlled trial which just made significance in regards to awareness rates.

In 2004 the B-Aware trial was the largest RCT on the subject published in the Lancet – showed BIS was better than “routine monitoring”

In 2007 the Cochrane group looked at the evidence – they found the data was a bit heterogeneous – “there may be an improvement” in recovery using BIS, but not enough cases of awareness to make a definitive statement about awareness.

In 2008 Avidan et al in the NEJM did an RCT comparing BIS to ET gas monitoring – and found no difference.  BIS not supported

Dr Tim (KI Docs) has sent me an interesting new article out of the NEJM which was pretty conclusive, much bigger numbers –  and it looked specifically at high risk patients.  and its conclusion: BIS is not superior to the traditional monitoring strategies – MAC or end-tidal volatile monitoring systems.  There was a trend towards an increased rate of awareness in the BIS group actually!

So is it worth the cost?  Maybe it has a place along side the other parameters – clinical, ET gas monitoring etc.  Does having another number in the mix increase our sensitivity for detecting awareness?  Or is it just another cost, one which smaller hospitals cannot afford?

Love to hear your opinions.   Do you BIS when you gas?  Casey


  1. It’s just another monitor…when used judiciously it can be useful. But I get worried when I see people relying on the BIS value ‘telling me patient is asleep’…despite other monitoring suggesting otherwise.

    My question is, is it worth the expense? We don’t have BIS in my small rural hospital back home. Should we? It’s not (yet) an ANZCA standard…so to make an argument for it’s inclusion (and it’s potentially expensive) one needs to make sure it value-adds to your technique (and this holds true for across any new gizmo in all areas of medicine).

    Best comment about BIS this weekend (currently working in a regional centre)? Long 36hr shift, multiple trauma, general surgery and obstetric cases….orthopaedic RMO wanders in to theatre to try and book a case and I say “Ah, great – are you here to help zero the BIS?”

  2. Jonathan Ramachenderan says

    Hey Casey

    Wow this anaesthetics year has been pretty great. With my Rural GP lens on everything I’ve learnt in theatres and consultants used to training Rural GP’s in our institution, you get an idea on what is essential for practice and what is just another number to worry about.

    The use for BIS that has been demonstrated to me for rural practice is when running a TIVA. I love running TIVA’s they are great for short gynaecological operations and patients often wake feeling much more refreshed with less PONV.

    So the use of BIS here is to keep the patient from being aware but keep them unconscious
    and immobile. Importantly it is also not to over sedate them with propofol.

    But I think using the body’s simple autonomic guide (pulse, respiratory rate, blood pressure and tears) and a knowledge of the pharmacokinetics of propofol in a TIVA is good enough to run without a BIS.

    So I won’t b freaking out next year when there isn’t a monitor in Albany! What I will be anxious to know is if they have a CMAC! My precious….

    Thanks Casey.

  3. Ah, a C-MAC…if only. Perhaps the Albany mob can afford it. I’ll be happy with my cheap n cheerful KingVision.

    Glad your JCCA year is going well. I wonder how many other procedural trainees there are out there? I wish there was a list…

  4. Minh Le Cong says

    Hi folks

    its a good idea to discuss the issue of awareness during anaesthesia, in particular in the rural and remote context. I am not convinced by the literature on BIS..conflicting stuff.

    There has been one paper written on its use in monitoring sedation for ventilated retrievals in an American aeromedical service. I had considered it for our aeromedical work

    Believe it or not we have had two reported cases of awareness during aeromedical transport for ventilated patients …I am sure there have been more that have gone unreported. When you review the sedation given it appears appropriate yet the patients report fairly consistent recall of things during the flight. It has made me question the efficacy of the good ole morphine/midazolam infusion which is de rigeur retrieval sedation for the ventilated patient.

    SO the problem is real..even on retrievals..I am just not convinced BIS is the answer!
    I agree with Jonathon about propofol TCI has been mathematically modelled and validated in a clinical can prove you are delivering the required concentration

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