23 General Anaesthesia and Oscillations in Human Physiology …
365
Thus, the search for better tools to monitor anaesthetic depth has gone on, along
different conceptual routes. One straightforward and quite successful approach has
simply been to monitor the exhaled end-tidal concentration of inhalational agents.
If the concentration of e.g. sevoflurane is at 1% or higher (or 3% with desflurane),
one can almost with 100% certainty assume that this patient will be asleep. Also,
refinements in looking at changes in sympathetic outflow have been promising [9]:
looking for subtle variations in the beat-to-beat interval on the EEG, measuring
pulse-plethysmography in the finger, looking at sweat-bursts in the palm of the hand
[14].
Still, none of these devices has even close to 100% specificity or sensitivity for
the state of general anaesthesia, in fact; most of them have not even been tested for
these features.
23.3 The Braccia Concept: Anaesthesia
Monitoring—Bringing it All Together?
The Braccia concept was developed as a result of physicists looking at the characteristics of numerous bio-rhythms in the body, noting that these change somewhat
predictably during sleep and general anaesthesia. Although these changes are not by
themselves highly specific or sensitive, the idea came up that bringing a number of
different low-specific changes together may increase the sensitivity and specificity.
The higher the number of relevant and different changes brought together, the higher
the chance of high specificity/sensitivity. The challenge in such a process will be to
first determine which changes and bio functions are relevant and non-overlapping.
Then build up an algorithm of bringing them together in a unified output for clinical
use.
The idea of combining different measures in this way is not new or original, and
attempts have been made and are being launched in this direction such as the PSI,
NOL index and others; using combinations of pulse-plethysmography signals and/or
EEG for a potentially more precise evaluation of anaesthetic depth.
The feature of the Braccia project was to start out very broadly, including most of
the documented measures of anaesthetic depth, refine the hardware for each measure,
measure simultaneously all measures in the same patients, then developing a complex
software program in order to sort out which measures were useful and in which way.
The first phase was the development of the hardware and the software for collecting
and analysing biorhythmic waves raw signals properly.
The second phase was to apply this prototype devices on a series of patients. The
clinical setup was highly standardized: All patents were monitored for about 30 min
in the awake state with relaxed and very quiet environment. Then general anaesthesia
was induced with either sevoflurane or propofol as a mono anaesthetic. After general
anaesthesia was established, the test battery was applied again for about 30 min
period of stable general anaesthesia with spontaneous ventilation.
365
Thus, the search for better tools to monitor anaesthetic depth has gone on, along
different conceptual routes. One straightforward and quite successful approach has
simply been to monitor the exhaled end-tidal concentration of inhalational agents.
If the concentration of e.g. sevoflurane is at 1% or higher (or 3% with desflurane),
one can almost with 100% certainty assume that this patient will be asleep. Also,
refinements in looking at changes in sympathetic outflow have been promising [9]:
looking for subtle variations in the beat-to-beat interval on the EEG, measuring
pulse-plethysmography in the finger, looking at sweat-bursts in the palm of the hand
[14].
Still, none of these devices has even close to 100% specificity or sensitivity for
the state of general anaesthesia, in fact; most of them have not even been tested for
these features.
23.3 The Braccia Concept: Anaesthesia
Monitoring—Bringing it All Together?
The Braccia concept was developed as a result of physicists looking at the characteristics of numerous bio-rhythms in the body, noting that these change somewhat
predictably during sleep and general anaesthesia. Although these changes are not by
themselves highly specific or sensitive, the idea came up that bringing a number of
different low-specific changes together may increase the sensitivity and specificity.
The higher the number of relevant and different changes brought together, the higher
the chance of high specificity/sensitivity. The challenge in such a process will be to
first determine which changes and bio functions are relevant and non-overlapping.
Then build up an algorithm of bringing them together in a unified output for clinical
use.
The idea of combining different measures in this way is not new or original, and
attempts have been made and are being launched in this direction such as the PSI,
NOL index and others; using combinations of pulse-plethysmography signals and/or
EEG for a potentially more precise evaluation of anaesthetic depth.
The feature of the Braccia project was to start out very broadly, including most of
the documented measures of anaesthetic depth, refine the hardware for each measure,
measure simultaneously all measures in the same patients, then developing a complex
software program in order to sort out which measures were useful and in which way.
The first phase was the development of the hardware and the software for collecting
and analysing biorhythmic waves raw signals properly.
The second phase was to apply this prototype devices on a series of patients. The
clinical setup was highly standardized: All patents were monitored for about 30 min
in the awake state with relaxed and very quiet environment. Then general anaesthesia
was induced with either sevoflurane or propofol as a mono anaesthetic. After general
anaesthesia was established, the test battery was applied again for about 30 min
period of stable general anaesthesia with spontaneous ventilation.