Sun28November0628PM 20

With regard to the bispectral index (BIS), which of the following are true?

True / False

It shows similar changes with all anaesthetic agents Correct

It predicts the response to surgical incision Incorrect answer selected

It decreases during normal sleep Correct

It is derived from the blood pressure and heart rate Correct

It predicts brain damage during cardiopulmonary bypass Correct

Explanation

The bispectral index (BIS) is a dimensionless number (0-100) that is a summative measurement of time domain, frequency domain and high order spectral parameters derived from electroencephalogram (EEG) signals.

Because sleep and anaesthesia have similar behavioural characteristics but are physiologically different, BIS monitors have been used to measure sleep depth. BIS levels decrease with increasing sleep depth during slow-wave sleep and this correlates with changes in regional cerebral blood flow when measured using positron emission tomography (PET).

BIS shows a dose-response relationship with the intravenous and volatile anaesthetic agents. Opioids whilst producing a clinical change in the depth of sedation or analgesia fail to produce significant changes in the BIS. Ketamine increases CMRO2 and EEG activity.

BIS is not able to predict movement in response to a surgical stimulus some of which are spinal reflexes and not perceived by the cerebral cortex.

Whilst BIS is used during cardiopulmonary bypass to measure depth of anaesthesia and an index of cerebral perfusion it cannot reliably predict subtle nor significant cerebral damage.

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Times answered: 237