To quote Goodman & Gilman :

An alternative way of defining the anesthetic state is to consider it as a collection of “component” changes in behavior or perception. The components of the anesthetic state include:
• amnesia
• immobility in response to noxious stimulation
• attenuation of autonomic responses to noxious stimulation
• analgesia
• unconsciousness

My question is, does not the state of Unconsciousness already imply other components of analgesia and amnesia? Analgesia is the absence of the perception of pain, which is granted if there is unconsciousness which would be the absence of all perceptions.

I am not certain if unconsciousness also entails amnesia, but it seems that remembering what happened when unconscious seems considerably unlikely.

Apart from a reductionist argument for minimizing the constraints required for classification as a general anesthetic, I am more interested in cases where unconsciousness would be achieved without analgesia or amnesia, which could be a likely rationale behind including the additional caveats in the definition.

  • $\begingroup$ Well, I looked up the definition from Merriam Webster. But I guess what you state could be classified under the reflex autonomic loops, which I don't think are included under unconsciousness. And I think, probably, that the sensation of pain would begin only when he becomes conscious. $\endgroup$ – stochastic13 Feb 22 '16 at 14:51
  • $\begingroup$ I guess the issue is what we mean by perception. If it strictly means stimuli perception, I guess it's not lost when unconscious. But I meant it more in the sensation way, the feeling of pain way. Sorry for the vague seemingly unscientific usage. $\endgroup$ – stochastic13 Feb 22 '16 at 14:55

A state of unconsciousness does not guarantee analgesia nor amnesia. Besides, a muscle relaxant is often paramount to prevent movements. The perfect general anesthetic would do all of this and have hypnotic, analgesic, amnesic and muscle relaxant properties. Such compounds do not exist, because each effect works on a different part of the brain or elsewhere.

In practice, therefore, multiple compounds are administered to obtain the desired effect. A cocktail anesthetic not only ensures all the desired physiological changes, it also reduces the chance of toxic side effects relative to giving one constituent in a large enough dose to encompass all the effects. And there lies an important point, namely anesthetic depth.

If anesthesia is deep enough, all effects may, perhaps, be reached to some degree with a single compound, but the dose likely becomes so high that the side effects become too large. An example in this realm is alcohol, which when consumed in copious amounts, may come close in reaching all desired effects at least to some degree. A related compound is ether. But even with ether, which has been used in early days of surgery, surgical stress caused patients to die intra-operatively due to cardiac hyperactivity. Surgical stress needs to be minimized and that's why an analgesic is needed in the cocktail.

Commonly applied anelgesics in the OR are opiates, such as fentanyl. Anelgesics are critical for invasice surgery, because the body reacts to trauma even when the brain cannot process the information to the degree necessary to turn it into a conscious experience.

For instance, a widely used cocktail is propofol-based anesthesia: A propofol injection might be used to start anesthesia, fentanyl (injectable) is used to blunt the stress response, midazolam (injectable) given to ensure amnesia, and sevoflurane (inhalant) during the procedure to maintain the effects.

  • $\begingroup$ Great answer! +1. I was hoping, though, that the answer would give a passing nod to the need for an amnestic. Not a very comforting prospect. $\endgroup$ – anongoodnurse Feb 26 '16 at 23:05
  • $\begingroup$ Thanks a lot for a great answer. But my primary concern was the discrepancy in the definition. If there is a loss of consciousness, can there be a memory of what transpires therein? Are there cases wherein a person can be rendered unconscious but still not amnesic about that state? And second, if I understand correctly, analgesia in the definition mean a loss of afferent nociceptor input and not just a loss of the perception of those inputs? $\endgroup$ – stochastic13 Feb 28 '16 at 11:47
  • 1
    $\begingroup$ A person may be unconscious but still can retain a feeling of something traumatic having happened during the surgery. This is called recall. You might want to read en.m.wikipedia.org/wiki/Anesthesia_awareness $\endgroup$ – Polisetty Mar 5 '16 at 10:39

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