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Renin Angiotensin Mechanism.

General Anesthetics.

General Anesthetics.



  • General anesthetics are the pharmacological agents which on administration produce loss of all modalities of sensations along with a reversible loss of consciousness.

  • They are used to perform major surgeries.

  • e.g. Anesthetic ether, Midazolam.


Anesthesia: -



  • Anesthesia is a medical technique of producing a reversible loss of sensations and awareness.

  • Anesthesia is of 3types

  • General Anesthesia:-

  • It is a total reversible loss of senses, reflex & consciousness.

  • It is used for major surgeries.

  • Local anesthesia:-

  • It is a localized reversible loss of sensation without affecting the consciousness of a patient.

  • It is used for minor surgical procedures like tooth extraction.

  • Spinal anesthesia:-

  • It is achieved by injecting a local anesthetic into spinal column at L2-L3- position (in subarachnoid space).

  • It is useful for surgeries of lower limb & gynecological procedures.

Classification of General Anesthetics:



  • General anesthetics can be classified as per their chemistry and pharmacology.

  • The pharmacological classification of general anesthetics is as follows,
Sr. No.

   Class                    Examples
A

Volatile or Inhalational Anesthetics

1)    Volatile Liquids.

·        Diethyl ether

·        Chloroform

·        Halothane.
2)    Gases.·        Nitrous Oxide.

·        Cyclopropane.
B
Non-Volatile or Intravenous Anesthetics

1)    Barbiturates·        Thiopentone Sodium.

·        Methohexitone Sodium.
2)    Benzodiazepines.·        Midazolam.

·        Diazepam.
3)    Opioid Analgesics.·        Fentanyl.
4)    Other·        Ketamine.

Ideal properties of general anesthetics:-



  • Faster induction of anesthesia.

  • Smooth recovery.

  • Easy to administer.

  • It should be non- inflammable & non- irritant.

  • Should produce good analgesia & adequate muscle relaxation.

  • Should have a wide margin of safety & there should be no side effects.

  • Should have sufficient duration of action.

  • Should not affect the liver, kidney, lungs & heart.

Stages of anesthesia:-


Stage 1:- Stage of analgesia.

Stage 2: Stage of delirium.

Stage 3: Stage of surgical anesthesia.

Stage 4: Stage of medullary paralysis.


Stage 1: Stage of analgesia.



  • It starts from beginning of anesthetic inhalation to loss of consciousness.

  • Pain is progressively reduced.

  • The patient remains conscious, can hear & see & feels a dream-like state.

  • Reflexes & respiration are normal.

  • Minor surgical procedures such as incision of abscess, dental extraction can be carried out during this stage.

Stage of delirium:-



  • This stage extends from loss of consciousness to the beginning of regular respiration.

  • The patient is in the excited state.

  • Breathing is rapid and jerky.

  • Heart rate, blood pressure may rise.

  • This stage is not suitable for any type of operative procedure.

  • Preanaesthetic medication is used to control the stage.

Stage 3: Stage of surgical anesthesia



  • It starts from the onset of regular respiration to end of spontaneous breathing.

  • It is characterized by steady respiration, fixed eyeballs with lost corneal and light reflexes.

  • This stage is suitable for major surgical operations as,

                                      Muscle tone is decreased.

                                      Breathing is regular.

                                      All reflexes are lost.

Stage 4: Stage of Medullary Paralysis



  • It starts from the cessation of breathing to the failure of circulation & death.

  • The patient should not reach this stage for which doses of anesthetics should be adjusted.

  • It is characterized by dropped respiration, heart rate, blood pressure.

  • Only prompt and vigorous efforts can save the life of a patient.

Mechanisms of action of  General Anesthetics:



  1. Inhalational anesthetics: potentiate GABA-A receptor linked chloride channel in thalamus & reticular activating system. Nitrous oxide inhibits excitatory glutamate receptor.

  2. Thiopentone, methohexitone & Midazolam are agonists of GABA-A receptor and act by opening the linked chloride ion channels to cause CNS depression.

  3. Ketamine inhibits excitatory glutamate receptor.

  4. Fentanyl is an agonist of Opioid receptors.

Preanesthetic Medication:



  • The medication given prior to anesthesia to make induction and recovery smoother is known as pre-anesthetic medication.

  • Objectives of pre-anesthetic medication:-

  • To reduce the dose of anesthetics.

  • To minimize adverse effects of anesthetics.

  • Proper preparation of the patient for anesthesia.

  • Relief from anxiety.

  • To reduce salivary & respiratory secretion.

  • To produce antiemetic effect extending to postoperative period.

  • To potentiate analgesic effect.

  • To produce adequate muscle relaxation prior to surgery.

  • Different classes of drugs are used as pre-anesthetic medication depending on the need of patient which is as follows….AnalgesicsE.g. Morphine (10 mg i.m.) or pethidine (50 mg i.m.) are used to potentiate analgesic effect.

    Antianxiety:

    E.g. Diazepam (5-10 mg oral) or lorazepam (2 mg i.m.) are used to reduce the anxiety of patient.

    Antisecretory:

    E.g. Atropine (0.6 mg i.m./i.v.) is used to reduce salivary & tracheobronchial secretion.

    H2 blocker:

    Ranitidine (150 mg oral) or famotidine (20 mg oral) is given to prevent gastric acidosis & stress ulcers.

    Antiemetic:-

    Metoclopramide (10-20 mg i.m.) is used to reduce postoperative vomiting. Ondansetron (4-8 mg i.v. ) is highly effective.

    Skeletal muscle relaxant. Succinylcholine or vecuronium or atracurium are used as musical relaxants.

  • Imagine Operations Without Anesthetics:

  •  
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