General Anesthesia

1. General Anesthesia Madan Baral B. Pharmacy Pokhara University

2. Contents Introduction and History of General anesthesia Properties of ideal General anesthetic Classification of General anesthetic agents Mechanism of Anesthesia Stages of Anesthesia Inhalation anesthetic agents Intravenous anesthetic agents Complications of General anesthesia Conclusion



3. Introduction General anesthetics (GAs) are drugs which produce reversible loss of all sensations and consciousness. Goal of anesthesia To create a reversible condition of comfort quiescence, and physiological stability in a patient before during and after performance of a procedure that would otherwise be painful frightening or hazardous.

4. Purpose Analgesia -loss of response to pain Amnesia -loss of memory, Immobility - loss of motor reflexes Hypnosis -loss of consciousness Skeletal muscle relaxation .

5. History of Anesthesia Ether synthesized in 1540 by Cordus Ether used as anesthetic in 1842 by Dr. Crawford W. Long Ether publicized as anesthetic in 1846 by Dr. William Morton Chloroform used as anesthetic in 1853 by Dr. John Snow Endotracheal tube discovered in 1878 Curare first used in 1942 - opened the “Age of Anesthesia”

6. Properties of an ideal anesthetic Property providing comfort to 3 personal Patient Surgeon Anesthetist

7. Physical Property Non -flammable, non-explosive at room temperature Stable in light. Liquid and vaporizable at room temperature i.e. low latent heat of vaporization . Stable at room temperature, with a long shelf life Stable with soda lime, as well as plastics and metals Environmentally friendly - no ozone depletion Cheap and easy to manufacture

8. Biological Properties Pleasant to inhale, non-irritant, induces bronchodilatation Low blood: gas solubility - i.e. fast onset High oil: water solubility - i.e. high potency Minimal effects on other systems - e.g. cardiovascular, respiratory, hepatic , renal or endocrine No biotransformation - should be excreted ideally via the lungs, unchanged Non -toxic to operating theatre personnel

9. Classification A. INHALATIONAL Gases Nitrous oxide Volatile Liquids Halothane Enflurane Isoflurane Desflurane Sevoflurane Methoxyflurane Trichloro - ethylene B. I.V. Ultra short B arbiturate Thiopental Non Barbiturate: Benzodiazepines Propofol Propanidid Neurolept analgesia Etomidate Ketamine

10. Inhaled Anesthetics

11. Anesthetic Machine

12. Minimal alveolar anesthetic concentration (MAC) Definition : It is the minimal alveolar anesthetic concentration at which 50 % of patients do not respond to a surgical stimulus Importance: I t is a measure of anesthetic potency , MAC is small for potent anesthetics, as halothane & large for weak anesthetics as N 2 O

13. Intravenous Anesthetics Used in combination with Inhaled anesthetics to: Supplement general anesthesia Maintain general anesthesia Provide sedation Control blood pressure

14. Mechanism of Action UNKNOWN!! Most Recent Studies: CNS depression by modifying the electrical activity of neurons at a molecular level by modifying functions of ION CHANNELS. Inhibitory transmission via the γ-aminobutyric acid a (GABA A ) receptor. N - methyl-d-aspartate ( NMDA) receptor (Ketamine).

15. Signs And Stages of Anesthesia GAs cause an irregularly descending depression of CNS The four stages of anesthesia were described in 1937

16. I. Stage of Analgesia also known as the " induction” period between the initial administration of the induction agents and loss of consciousness . Activities The patient progresses from analgesia without amnesia to analgesia with amnesia. Conversation possible

17. II. Stage of Delirium A lso known as the "excitement or delirium stage” P eriod following loss of consciousness and marked by excited and delirious activity. Activities Respirations and heart rate may become irregular. U ncontrolled movements Vomiting Breath holding Pupillary dilation Irregular respiration

18. III. Stage of Surgical Anesthesia Activities The skeletal muscles relax Patient's breathing becomes regular. Eye movements slow, then stop, and surgery can begin. And divided into 4 planes: E yes initially rolling, then becoming fixed Loss of corneal and laryngeal reflexes Pupils dilate and loss of light reflex Intercostal paralysis, shallow abdominal respiration, dilated

19. IV. Medullary paralysis A lso known as " overdose” Cessation of respiration Potential cardiovascular collapse L ethal without cardiovascular and respiratory support.

20. Complication of General Anesthesia A. During anesthesia Respiratory depression and hypercapnea Salivation , respiratory secretions -less now as non- irritant anesthetics are mostly used. Cardiac arrhythmias Fall in BP Laryngospasm and asphyxia Delirium convulsions. Excitatory effects are generally
seen with I.V.

21. B. After anesthesia Nausea and vomiting. Persisting sedation: impaired psychomotor function Pneumonia, atelectasis Organ toxicities: liver, kidney damage. Nerve palsies - due to faulty positioning. Emergence delirium.

22. To Sum Up The modern day surgery would be impossible with out GAs. Surge for Research: M ost convincing mechanism of action Discover ideal anesthetics with least side effects

23. References Fardman , Limbird , Gilman(2001), The Pharmacological Basis of Therapeutics (10 th Ed.), McGraw Hill, New Delhi, pp 321-333,337-343 Koda -Kimble Young (2000) Applied Therapeutics: The Clinical Use of Drugs (7 th Ed.), Lipincott Williams & Wilkins, Baltimore , pp 8.6-8.13 URL1- http:// en.wikipedia.org / wiki/ General_anaesthesia

24. Thank You