Abstracts and Programme: EUROANAESTHESIA 2011: The European Anaesthesiology Congress: Neurosciences
Background and Goal of Study: Functional electrical impedance tomography by evoked response (fEITER) is a novel neuroimaging device which measures internal electrical impedance across the brain using a temporal resolution of 10ms. Sub-second activity deep within the brain has been visualised for the first time during induction of anaesthesia. We aimed to reconstruct loss of consciousness in real time as a 3D movie and calibrate fEITER for future clinical work.
Materials and Methods: fEITER injects current sequences of 1 mA peak-topeak at 10 kHz. 32 ZipPrep™ (Covidien) electrodes were placed on the scalp. A high resolution ECG was simultaneously recorded. Continuous electrical impedance data was captured using fEITER across non-current electrode pairs for all trials lasting 1 minute. A trial comprising 20 patients scheduled for surgery is currently underway. We report the first reconstructions from EIT data during induction of anaesthesia with propofol.
Results and Discussion: Reconstructed images of sub-second impedance changes show loss of consciousness as anaesthesia is induced with propofol (figure 1)3111.
A concurrent decrease in BIS value was observed. The potentiating effects of propofol on inhibitory neurotransmitters in the brain have been visualised for the first time. Unconsciousness is the increase of inhibitory assemblies across the cortex. These findings support Greenfield's hypothesis of neural assemblies forming consciousness2.
Conclusion: Anaesthetic induction has been visualised for the first time showing a real time loss of consciousness in anatomically distinct regions of the brain. fEITER has potential clinical utility in awake and anaesthetised individuals, with no safety implications.
1Holder DS. Electrical impedance tomography (EIT) of brain function. Brain Topogr. 1992;5; 87-93.
2Greenfield S. Mind, brain and consciousness. Br J Psychiatry. 2002; 181; 91-3.
Acknowledgements: Wellcome Trust funded. fEITER is patented. ISRCTN No: 93596854