Minimum Alveolar concentration
MAC is the minimum amount of the anaesthetic in the pulmonary alveoli that is required to produce immobility in the response to painful stimuli used in dose fixation and Capacity of anaesthetic is measured.Classification
Classification of General Anaesthetics
A.Inhalational Anaesthetics –1. Volatile liquids- Chloroform, Diethyl ether, Trichloroethylene, Halothane, Enflurane & Isoflurane.
2. Gases- Cyclopropane, Nitrous oxide, chloroform & Cyclopropane.
B. Non – volatile (I.V.) Anaesthetics –
1. Inducing agents: - Thiopentone sodium, Etomidate, Propafol.
2. Slower acting drugs: - a) Benzodiazepines (BZDs) – Diazepam, Lorazepam and Midazolam.
b) Dissociative Anaesthetics: - Ketamine.
c) Neurolept Analgesia: - Fentanyl + Droperdiol.
(Analgesic) (Butyrophenone).
Mechanism of Action
Most of the GA acts by blocking the synaptic transmission but some act by blocking excitatory transmission but some act by prolonging the synaptic inhibition (Potentiation of GABA-A ) thus depressing all the functional elements of CNS.Inhalational anaesthetics, Barbiturates and Benzodiazepines (BZDs) act by potentiating the action of the inhibitory neurotransmitter GABA at GABAA receptor.
Ketamine selectively inhibits the excitatory NMDA type of glutamate receptor.
Stages of Analgesia-
1. Stage of analgesia – Minor surgical procedures such as incision of Abcess, dental extraction are carried successfully at this stage.2. Stage of delirium – Must be avoided.
3. Stage of surgical anaesthesia – Includes 4 Planes.
4. Stage of respiratory Paralysis
Pre-anaesthetic medication
The term applied to the use of drugs prior to the administration of an anaesthetic agent, with the objective of making anaesthesia safer & more agreeable to the patient.1. Opoid analgesics – Morphine, Pethidine, Buprenorphine to reduce anxiety &
the apprehension of the patient.
2. Sedative & Tranquilizers – Benzodiazepines& Barbiturates.
3. Anticholinergics – Atropine or Scopalamine.
4. Antiemetics – Phenothiazines(Promethazine & trimeprazine), Metoclopramide.
5. H2 Blockers – Ranitidine & famotidine to avoid gastric regurgitation & aspiration pneumonia.
6. Neuroleptics – Cpz, triflupromazine
