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


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