General Anesthesia and their Anesthetic drugs l Study Pharma l

General Anesthesia and their drugs

 General anesthetics:

General anesthetics are those drugs that produce reversible loss of consciousness in patients to proceed major operation.

Features of General anesthetics:

- Loss of consciousness

- Sleep and amnesia

- Loss of somatic and autonomic reflexes

- Immobility and muscle relaxation

Minimal alveolar concentration (MAC):

- Minimal alveolar concentration (MAC) is the lowest concentration of general anesthetic drug required in the pulmonary alveoli to produce immobility in response to a painful stimulus in 50% of individual or population.

(Minimal alveolar concentration of all inhalation anesthetic decline with age beyond 50 years)

- MAC of general anesthetic drugs shows a excellent oil/gas partition coefficient that reflect capacity of anesthetic enter into the central nervous system (CNS) and attain sufficient concentration to produce unconscious in patient.

Mechanism action of General anesthetics:

Different anesthetic drugs produce anesthesia action by different mechanism but also exhibit stereospecific effect involve the cerebrospinal axis:-

* Unconscious appears to be in thalamus and reticular activating system

- Amnesia may be a result of cerebral cortex and hippocampus.

- Immobility may be a result of spinal cord.

* Major target of anesthetic action are ligand gated ion channels.

- In this, GABAa receptor gated chloride ion channel complex is main.

- Many inhalation anesthetics like barbiturates, benzodiazepines are interact with its own binding site on GABAa receptor gated chloride ion channel complex by activating chloride ion channel and intake of chloride ions from outside to inside of the neuronal membrane.

- Action of glycine (act as a inhibitory transmitter which also activates chloride ion channels) in spinal cord and medulla is augmented by many inhalation anesthetic drugs and barbiturates.

This action may block the responsiveness to painful stimuli resulting in immobility and muscle relaxation, sleep and amnesia, loss of somatic and autonomic reflexes and abolition of pain.

- On the other hand, nitrous oxide and ketamine do not affects GABA or glycine gated chloride ion channel rather they selectively NMDA type glutamate receptors responsible for calcium ion channel in neurons.

(General anesthetic drugs act by depressing the synaptic transmission (because of the inhibitory of presynaptic transmission as well as postsynaptic activation).

Stages of Anesthesia:

* Stage of Analgesia

* Delirium

* Surgical Anesthesia

* Medullary paralysis

*Stage of Anesthesia:

This stage start from beginning of anesthetic inhalation and last up to the loss of consciousness.

- Pain abolished

- Patient remain conscious, can hear and see, feel dream like state.

- Amnesia start at end of this stage.

- Reflexes and respiration remain normal.

- Some minor operation can be carried out during this stage (limited to short duration procedure).

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