The Value to the Anaesthetist of Monitoring Cerebral Activity

Abstract

Abstract:The administration rate of general anaesthetic drugs is at present guided by clinical experience, and indirect indicators such as haemodynamic parameters. In the presence of muscle relaxants most of the clinical signs of inadequate anaesthesia are lost and accidental awareness may occur. A number of monitoring modalities, primarily based on analysis of the electroencephalogram (EEG), have been proposed for measurement of the anaesthetic depth. Moreover intraoperative cerebral monitoring may also provide the anaesthetist with early warning of cerebral ischaemia, or information on specific neurological pathways. To facilitate this, it is essential to combine analysis of the spontaneous EEG with recording of evoked potentials, to assess both cortical and subcortical activity/events. None of the reviewed methods, however promising, can alone meet all of the requirements for intraoperative monitoring of cerebral function. We suggest that the future direction should be to integrate several modalities in a single device, to provide valuable new information, upon which to base clinical management decisions.

Respiratory sinus arrhythmia during anaesthesia: assessment of respiration related beat-to-beat heart rate variability analysis methods

“…Langford and Thomsen concluded that no single measure derived from electroencephalogram, sensory evoked potentials or heart rate variability can alone meet all of the requirements for intraoperative monitoring of cerebral functions [19]. Our previous studies support this, showing the correlation between EEG transients and heart rate [20], as well as the reversed phase relationship of RSA during positive pressure ventilation [15].…”

Model-Based Biosignal Interpretation II

“…The contribution by Kawahara et al: Interactions between respiratory, cardiac and stepping rhythms in decerebrate cats: functional hierarchical structures of biological oscillators [4] is in many aspects very similar to the previous one. The authors show care in well defining the problem, the biological signals under study and the signal processing methods they have applied, mainly the coherence function to estimate the coupling strength between respiratory, cardiac and stepping rhythms during fictive locomotion in cats.…”

“…The work presented in the two previous papers has been achieved thanks to a close collaboration between physiologists and engineers. There is evidence of another fruitful collaboration between physicians and scientists in the paper from Langford and Thomsen [4]. They provide an excellent, lucid discussion on "The value to the anesthetist of monitoring cerebral activity".…”

“…A common understanding is that a Model-Based Biosignal Interpretation process is based on knowledge ~ models which "may help to provide an )interpretation of the available biosignals in terms of the physiological status of the patient" [1]. Among the four papers in this Section, two have a cognitive outcome [2,3] and one is decision oriented [4]. The last paper from Jensen, Demant and Sanchez [5] is very different in its objectives: it describes a new noise-cancelling biosignal processing tool which has been designed assuming that both the model of the signal and of the additive noise are known.…”