Oxford University researchers have shown that measuring a type of brain activity in an individual under anaesthetic offers the clearest picture yet of degrees of perceptual awareness in the brain while they are anaesthetised.
The research could lead to the first personalised method for administering appropriate doses of anaesthetic during operations and potentially reduce the risks associated with being under a general anaesthetic.
'Despite the hundreds of thousands of anaesthetics administered daily to patients, remarkably there is no robust, individualised indicator of perceptual awareness available,' said Professor Irene Tracey of the University of Oxford and senior author of the paper. 'While we can indirectly gauge whether a patient physically responds to their environment, this imaging method offers a much more nuanced approach.'
She added: 'The next stage in the development of this method will be to see if it is similarly illuminating when we monitor anaesthetised patients undergoing surgery.'
The work was carried out at the University of Oxford in the Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB) and is published in the journal Science Translational Medicine. The study was funded by the Medical Research Council (MRC), the Wellcome Trust, International Anesthesia Research Society and the National Institute of Academic Anaesthesia.
Currently, when an individual is given anaesthetic for an operation, their organs' responses are monitored around the body, such as heart rate and rate of respiration. But there is no direct, accurate method with which to pinpoint their brain's level of consciousness.
While the risk of side-effects from anaesthetic is low and the risk of waking up during an operation lower still, older people and those with cardiac or neurological problems remain more vulnerable to complications from the administration of unnecessarily high doses of anaesthetics.
The research team administered a standard anaesthetic, propofol, over an extended period of time to 16 subjects and exposed the subjects to different kinds of stimuli, while recording the brain's electrical activity using electroencephalography (EEG).
By measuring slow-wave activity in the brain, they found that there were common patterns of behaviour among the group as they lost consciousness – but that these behaviours happened at different times unique to each individual.
They found that beyond the stage where they stopped responding to standard external stimuli, subjects reached a state where the slow-activity waves in the brain stayed the same, even as higher doses of anaesthetic were given.
Functional magnetic resonance imaging (fMRI) data helped reveal that at this saturation of the slow wave activity, the brain became ‘isolated’ from the external world. The brain regions that would usually be expected to respond to standard stimuli were no longer activated.
This indicates that there is an optimum depth of anaesthesia producing perception loss beyond which further anaesthetic is not needed.
Professor Hugh Perry, Chair of the Neurosciences and Mental Health Board at the MRC, said: 'With the growing use of anaesthetics in the elderly and other at-risk groups, understanding the minimal dose required to induce the necessary level of anaesthesia is hugely important. This work, part-funded by the MRC, is an excellent example of implementing cutting-edge imaging techniques in a way that provides an excellent scientific foundation for new ways of treating vulnerable patients.'