Liquid Journal of Complex Systems

Article #9, version 15 March 2012, state: Liquid turbulent

A Success Story in the Science of Complex Systems: Nonlinear Dynamics of Anaesthesia

Authors: Aneta Stefanovska, Peter V. E. McClintocki

Abstract

In anaesthesia a chemical perturbation of the organism leads to a temporary loss of consciousness, but just how this happens remains to a large extent a mystery. Perhaps on account of this lack of deep understanding, there are not yet any reliable markers for depth of anaesthesia. Consequently, as C.Pomfrett put it, “...the anaesthesist is still unable to measure the depth of anaesthesia in order to preven inadvertent awakening during anaesthesia." It is perhaps not surprising, therefore, that the incidence of awareness among patients undergoing surgery is nonzero. The problem can be particularly severe in cases where for clinical reasons the anesthesia is kept as light as possible, and where a mechanically ventilated curarised patient is unable to give any voluntary indication of awareness. A number of different methods have been proposed for assessment of depth of anaesthesia, but none is 100% reliable or accurate. They involve e.g. measurements of changes in heart rate variability (HRV) and cardio-respiratory coupling, as well as the bispectral index monitor known as BIS (Aspect Medical Systems) for which the algorithm by which the machine works remains a closely guarded secret. The BRACCIA consortium took such ideas much further, partly by adopting more sophisticated mathematical analyses of the data, including analyses of directions of coupling, and partly by looking at possible interactions between cardiovascular and neural (cortical) oscillations. The consortium has investigated the complex interactions between brain waves and cardio-respiratory oscillations that occur during anaesthesia. Investigations had shown that marked changes occur in the inter-oscillator interactions during anesthesia. It was hypothesised that these could perhaps form a new basis for measurement of depth of anesthesia, and BRACCIA performed the basic research needed to explore this possibility.

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Received: 15 March 2012 | Updated: 15 March 2012 | Liquid turbulent since: 15 March 2012

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