Theories Of General Anaesthetic Action
A general anaesthetic (or anesthetic) is a drug that brings about a reversible loss of consciousness. These drugs are generally administered by an anaesthetist/anaesthesiologist in order to induce or maintain general anaesthesia to facilitate surgery.
General anaesthetics have been widely used in surgery since 1842 when Crawford Long for the first time administered diethyl ether to a patient and performed a painless operation. It has always been believed that general anaesthetics exert their effects (analgesia, amnesia, immobility) by modulating the activity of membrane proteins in the neuronal membrane. However, the exact location and mechanism of this action are still largely unknown although much research has been done in this area. There are a number of outdated and modern theories that attempt to explain anaesthetic action.
The concept of specific interactions between receptors and drugs first introduced by Paul Ehrlich states that drugs act only when they are bound to their targets (receptors). However, this concept is not working well in case of general anaesthetics because:
- Molecular structures of general anaesthetics widely used in medicine are very simple and diverse so that there is no obvious structure–activity relationship (see structures of general anaesthetics widely used in medicine: 1-ethanol, 2- chloroform, 3-diethylether, 4-fluroxene, 5-halothane, 6-metheoxyflurane, 7- enflurane, 8-isoflurane, 9-desflurane, 10-sevoflurane)
- Most general anaesthetics have remarkably weak affinity for their targets acting at much higher concentrations than most other drugs so that diverse side effects are inevitable .
All these common features of general anaesthetics made it hard for early researchers to believe that general anaesthetics act in a specific manner and their action on neuronal membrane was thought to be global (through nonspecific perturbation of lipid membrane of CNS neurons) rather than through specific sites.
Read more about Theories Of General Anaesthetic Action: Lipid Solubility-anaesthetic Potency Correlation (the Meyer-Overton Correlation), Outdated Lipid Hypotheses of General Anaesthetic Action, Modern Lipid Hypothesis, Membrane Protein Hypothesis of General Anaesthetic Action
Famous quotes containing the words theories of, theories, general and/or action:
“Theories of child development and guidelines for parents are not cast in stone. They are constantly changing and adapting to new information and new pressures. There is no “right” way, just as there are no magic incantations that will always painlessly resolve a child’s problems.”
—Lawrence Kutner (20th century)
“The wise man regulates his conduct by the theories both of religion and science. But he regards these theories not as statements of ultimate fact but as art-forms.”
—J.B.S. (John Burdon Sanderson)
“The happiest conversation is that of which nothing is distinctly remembered but a general effect of pleasing impression.”
—Samuel Johnson (1709–1784)
“For the child whose impulsiveness is indulged, who retains his primitive-discharge mechanisms, is not only an ill-behaved child but a child whose intellectual development is slowed down. No matter how well he is endowed intellectually, if direct action and immediate gratification are the guiding principles of his behavior, there will be less incentive to develop the higher mental processes, to reason, to employ the imagination creatively. . . .”
—Selma H. Fraiberg (20th century)