Surgery – Diagnostic testing – Detecting brain electric signal
Patent
1997-12-02
1999-04-06
Getzow, Scott M.
Surgery
Diagnostic testing
Detecting brain electric signal
A61B 50484
Patent
active
058910506
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the monitoring of a subject's general state of health, more specifically to a method and a device for determining and monitoring the degree of narcosis in a subject according to the preamble to claim 1 and the preamble to claim 10 in the appended claims.
BACKGROUND OF THE INVENTION
In connection with a surgical operation, it is often necessary to lower the patient's degree of consciousness to make it possible to carry out the operation. Therefore, the patient is put under anaesthetic. Anaesthesia in connection with surgical operations, however, is always combined with serious risks for the patient. Thus, the following serious, undesirable states may arise: on in the operating theatre. This can be experiences to be very unpleasant and can make the patient suffer mentally. around him. This state is very unpleasant and can make the patient suffer mentally.
The states 1 and 2 occur owing to too low a degree of narcosis, whereas the state 3 is the result of over-dosing. Apart from the wish to prevent the above-mentioned serious consequences of incorrect dosing, there is a general wish to use as low a degree of narcosis as possible in order to shorten the time of awakening. This yields in a minimum effect on the patient and besides reduces the public nursing expense. Therefore there is a strong wish to be able to accurately determine the degree of narcosis, which is also called anaesthetic depth.
The monitoring of narcosis during surgical operation, however, is still a clinical problem. Modern surgery and the development of new anaesthetics have, if anything, accentuated this problem. Certainly the technical progress in the monitoring of narcosis has made it possible to follow vital parameters such as oxygen saturation, blood pressure, and the concentration of anaesthetic in the exhalation air. These possibilities, however, do not give a direct measure of the patient's anaesthetic depth, but they merely result in a rough picture of the patient's state. Moreover, there is a strong dependence on the type of anaesthetic used and the other drugs used in connection with the operation.
Progress in neurophysiological measuring methods has caused expectations of being able to continuously follow the patient's anaesthetic depth. In recent years, much research has been directed to the measuring of cerebral electric activities during anaesthesia and similar states with a reduced level of consciousness. A general example is the measuring of conventional EEG (electroencephalogram), which has not given any results. However, there have recently been reports on a so-called auditory evoked potential, i.e. an electric stimulus response to auditory stimulation, containing the necessary information. For comparison, it can be mentioned that EEG reflects the system at rest. Auditory evoked potential reflects the level of cerebral activities and is today used routinely for diagnosing hearing disorders by means of a brainstorm audiometer.
A brainstem audiometer registers the variation in voltage that occurs between two electrodes placed on the head when the brainstem and the auditory nerve are activated in acoustic stimulation. The response that is registered by the brainstem audiometer is part of an auditory electric response, AER, which is generated in the auditory chain, i.e. the auditory nerve and different parts of the brain, in acoustic stimulation.
The auditory electric response is usually divided in time as follows. Early responses (0-2 ms), quick responses (2-10 ms), medium-late responses (10-50 ms) and late or slow responses (50-300 ms).
In the range of early responses there is the summed-up action potential from the auditory nerve which is derived from the inner ear and the auditory nerve and which is registered by means of a technique called electrocochleography (EcoG). In the range of quick responses, there is the brainstem response that is generated in the auditory nerve and the brainstem and which consequently is registered by means of a technique called brainstem audi
Gansler Tomas
Hansson Maria
Getzow Scott M.
SCS Medicinproject Aktiebolag
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