362
J. Raeder
widespread and frequent in use, there are still many controversies to this concept,
such as: How is general anaesthesia defined? What is the mechanism of general
anaesthesia? What drugs are useful for the purpose and which are best? How do we
measure and or quantify general anaesthesia?
23.1 Definition and Mechanisms
Definition of anaesthesia and mechanisms of general anaesthesia are linked, as for
most biological phenomena there is a relationship between mechanism of action
and resultant physiological effects, leading to the physiologic response or state of
function which is in question. Not quite so simple with general anaesthesia, even
though some distinct receptors and biological actions may be identified for most of
the drugs which produce the state of general anaesthesia. Still, general anaesthesia
seems to be a fundamental physiologic state of living animals and even plants [7],
being the result of a number of very different measures. If we look at immobility and
unconsciousness as the two major features, these may be the results of, for instance;
diabetic coma, liver coma, a hard blow to the head, overdose of most psychoactive
drugs etc. However, the features of clinical general anaesthesia are, in addition to
unconsciousness and immobility, rapid reversibility of the condition without any
damage of the organism. This may be accomplished by inhalational anaesthetic
agents, some iv agents, and hypnotic acting agents in combination with opioids.
Still, looking at the molecular structures and their potential actions on human nerve
cells, these anaesthetic drugs are quite different from each other. Their actions may
be described in terms of cellular targets, but also in terms of altered intercellular
interactions, altered neuronal network modes and specific anatomical regions [5].
As to cellular actions we know that most of the hypnotics acts at the GABA
receptor, the opioids at the opioid my-receptor [15], ketamine at the NMDA receptor,
whereas inhalational agents have a more complex and diversified action. We know
that attenuation of neuronal activity in the dorsal spinal horn is a major player in
immobility, and attenuation of reflex actions to nociceptive (i.e. painful in the awake)
stimuli is important for attenuation of discomfort. Further, downregulation of activity
in the cerebral cortex is a major feature of unconsciousness, although in the state
of anaesthetic induced unconsciousness there are areas in the deeper brain with
increased activities as well. Thus, this brings in the important concept of general
anaesthesia and unconsciousness as altered signal patterns within the very complex
neuronal network in the central nervous system.
23.2 Monitoring of General Anaesthesia
Monitoring of general anaesthesia is conceptually very difficult, both because of
the variety of different drugs and drugs actions involved, as well as the extreme
complexity of the target organ: the central nervous system. In the brain and spinal
J. Raeder
widespread and frequent in use, there are still many controversies to this concept,
such as: How is general anaesthesia defined? What is the mechanism of general
anaesthesia? What drugs are useful for the purpose and which are best? How do we
measure and or quantify general anaesthesia?
23.1 Definition and Mechanisms
Definition of anaesthesia and mechanisms of general anaesthesia are linked, as for
most biological phenomena there is a relationship between mechanism of action
and resultant physiological effects, leading to the physiologic response or state of
function which is in question. Not quite so simple with general anaesthesia, even
though some distinct receptors and biological actions may be identified for most of
the drugs which produce the state of general anaesthesia. Still, general anaesthesia
seems to be a fundamental physiologic state of living animals and even plants [7],
being the result of a number of very different measures. If we look at immobility and
unconsciousness as the two major features, these may be the results of, for instance;
diabetic coma, liver coma, a hard blow to the head, overdose of most psychoactive
drugs etc. However, the features of clinical general anaesthesia are, in addition to
unconsciousness and immobility, rapid reversibility of the condition without any
damage of the organism. This may be accomplished by inhalational anaesthetic
agents, some iv agents, and hypnotic acting agents in combination with opioids.
Still, looking at the molecular structures and their potential actions on human nerve
cells, these anaesthetic drugs are quite different from each other. Their actions may
be described in terms of cellular targets, but also in terms of altered intercellular
interactions, altered neuronal network modes and specific anatomical regions [5].
As to cellular actions we know that most of the hypnotics acts at the GABA
receptor, the opioids at the opioid my-receptor [15], ketamine at the NMDA receptor,
whereas inhalational agents have a more complex and diversified action. We know
that attenuation of neuronal activity in the dorsal spinal horn is a major player in
immobility, and attenuation of reflex actions to nociceptive (i.e. painful in the awake)
stimuli is important for attenuation of discomfort. Further, downregulation of activity
in the cerebral cortex is a major feature of unconsciousness, although in the state
of anaesthetic induced unconsciousness there are areas in the deeper brain with
increased activities as well. Thus, this brings in the important concept of general
anaesthesia and unconsciousness as altered signal patterns within the very complex
neuronal network in the central nervous system.
23.2 Monitoring of General Anaesthesia
Monitoring of general anaesthesia is conceptually very difficult, both because of
the variety of different drugs and drugs actions involved, as well as the extreme
complexity of the target organ: the central nervous system. In the brain and spinal