Anesthetic Agents & Anesthesia

• Anesthesia is the loss of sensation by giving anesthetic agents.
• Agents which cause the loss of sensation are called as anesthetic agents.

These are of two types;

Local

• These cause loss of sensation but animal is conscious.

General

• These cause loss of sensation due to unconsciousness.

Objectives of Anesthesia

• Sensory block to have analgesia. In this, sensory stimuli from the periphery are blocked.
• Mental block to have hypnosis or Amnesia (animal know nothing, what is happening around). Activity of CNS is blocked.
• Motor block to have muscle relaxation
• Reflex block to have hyporeflexia
• In case of local anesthetics, only one purpose is not the case of interest which is the mental block.

Stages of Anesthesia

• Based on ether anesthesia, there are following stages of anesthesia;
• Excitement stage (voluntary movements occur)
• Delirium stage (involuntary movements occur)
• Surgical Stage
• Medullary paralysis

There are 3 stages of anesthesia;

• Induction
• Maintenance
• Recovery

Ideal Properties of Anesthetic Agent

• It should cause rapid & smooth induction and recovery.
• It should be easy to maintain anesthesia (light or deep).
• It should be non-toxic and safe to internal organs.
• It should be non-irritant.
• It should be non-inflammable and non-explosive.
• Myocardial sensitization to epinephrine should be least.
• It should be compatible with other drugs.
• It should be easily available, cheap and easy to administer.

Pre-anesthetic Agents

These are the drugs given before anesthesia.

Why to give?

• To reduce anxiety of patient
• To reduce the amount of anesthetic agent
• To reduce the adverse effects of anesthetic agent
• To reduce the toxicity problems
• To reduce secretions especially Bronchial & Salivary
• To increase analgesia

Examples

• Opiods (Morphine, Mepridine) which induce analgesia
• Tranquilizers (Xylazine, Acepromazine) which reduce anxiety
• Anticholinergic drugs (Atropine sulphate, scopolamine) which reduce secretions
• Muscle relaxants (Gallamine, Pancuronium, d-tubocurarine, succinylcholine)

Medication during Anesthesia

• To reduce Blood pressure
• To induce muscle relaxation
• To stop bleeding

Post-Anesthetic Medication

• Analgesics
• Anti-inflammatory
• Anti-microbial
• Cholinergic drugs to relieve retention of urine E.g. Bethanicol