General Anesthesia

Madan BaralB. Pharmacy

Pokhara University

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

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.

Purpose

• Analgesia-loss of response to pain

• Amnesia-loss of memory,

• Immobility- loss of motor reflexes

• Hypnosis-loss of consciousness

• Skeletal muscle relaxation.

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”

Properties of an ideal anesthetic

• Property providing comfort to 3 personalPatient SurgeonAnesthetist

Physical Property1. Non-flammable, non-explosive at room

temperature2. Stable in light.3. Liquid and vaporizable at room temperature i.e.

low latent heat of vaporization .4. Stable at room temperature, with a long shelf life 5. Stable with soda lime, as well as plastics and metals6. Environmentally friendly - no ozone depletion 7. Cheap and easy to manufacture

Biological Properties1. Pleasant to inhale, non-irritant, induces

bronchodilatation

2. Low blood: gas solubility - i.e. fast onset

3. High oil: water solubility - i.e. high potency

4. Minimal effects on other systems - e.g. cardiovascular, respiratory, hepatic, renal or endocrine

5. No biotransformation - should be excreted ideally via the lungs, unchanged

6. Non-toxic to operating theatre personnel

ClassificationA. INHALATIONALGases

• Nitrous oxide Volatile Liquids

• Halothane• Enflurane • Isoflurane• Desflurane • Sevoflurane• Methoxyflurane • Trichloro-ethylene

B. I.V. Ultra short Barbiturate

• Thiopental Non Barbiturate:

• Benzodiazepines • Propofol• Propanidid • Neurolept analgesia• Etomidate • Ketamine

Inhaled Anesthetics

Anesthetic Machine

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: It is a measure of anesthetic potency, MAC is small for potent anesthetics, as halothane & large for weak anesthetics as N2O

Intravenous Anesthetics

Used in combination with Inhaled anesthetics to:

• Supplement general anesthesia

• Maintain general anesthesia

• Provide sedation• Control blood pressure

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 (GABAA) receptor.

– N- methyl-d-aspartate (NMDA) receptor (Ketamine).

Signs And Stages of Anesthesia

• GAs cause an irregularly descending depression of CNS

• The four stages of anesthesia were described in 1937

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

II. Stage of Delirium• Also known as the "excitement or delirium stage”• Period following loss of consciousness and marked by

excited and delirious activity. Activities • Respirations and heart rate may become irregular.• Uncontrolled movements• Vomiting• Breath holding • Pupillary dilation• Irregular respiration

III. Stage of Surgical AnesthesiaActivities• The skeletal muscles relax• Patient's breathing becomes regular. • Eye movements slow, then stop, and surgery can

begin. And divided into 4 planes:1. Eyes initially rolling, then becoming fixed2. Loss of corneal and laryngeal reflexes3. Pupils dilate and loss of light reflex4. Intercostal paralysis, shallow abdominal respiration,

dilated

IV. Medullary paralysis• Also known as "overdose”• Cessation of respiration • Potential cardiovascular collapse• Lethal without cardiovascular and respiratory

support.

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

generallyseen with I.V.

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.

To Sum Up• The modern day surgery would be impossible with

out GAs.• Surge for Research:

Most convincing mechanism of actionDiscover ideal anesthetics with least side effects

References1. Fardman, Limbird, Gilman(2001), The Pharmacological Basis of

Therapeutics(10th Ed.), McGraw Hill, New Delhi, pp 321-333,337-

343

2. Koda-Kimble Young (2000) Applied Therapeutics: The Clinical Use

of Drugs (7th Ed.), Lipincott Williams & Wilkins, Baltimore, pp 8.6-

8.13

3. URL1-http://en.wikipedia.org/wiki/General_anaesthesia

Thank You