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
• General anesthetics (GAs) are drugs which
produce reversible loss of all sensations and
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.
• 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 personal
1. Non-flammable, non-explosive at room temperature
2. 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 metals
6. Environmentally friendly - no ozone depletion
7. Cheap and easy to manufacture
1. 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
6. Non-toxic to operating theatre personnel
Minimal alveolar anesthetic
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
Used in combination with
Inhaled anesthetics to:
• Supplement general
• Maintain general
• Provide sedation
• Control blood pressure
Mechanism of Action
• 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)
– N- methyl-d-aspartate (NMDA)
Signs And Stages of Anesthesia
• GAs cause an irregularly descending depression of
• The four stages of anesthesia were described in
I. Stage of Analgesia
• also known as the "induction”
• period between the initial administration of the
induction agents and loss of consciousness.
• 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.
• Respirations and heart rate may become irregular.
• Uncontrolled movements
• Breath holding
• Pupillary dilation
• Irregular respiration
III. Stage of Surgical Anesthesia
• 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 fixed
2. Loss of corneal and laryngeal reflexes
3. Pupils dilate and loss of light reflex
4. Intercostal paralysis, shallow abdominal
IV. Medullary paralysis
• Also known as "overdose”
• Cessation of respiration
• Potential cardiovascular collapse
• Lethal without cardiovascular and respiratory
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.
B. After anesthesia
• Nausea and vomiting.
• Persisting sedation: impaired psychomotor
• 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
• Surge for Research:
Most convincing mechanism of action
Discover ideal anesthetics with least side effects
1. Fardman, Limbird, Gilman(2001), The Pharmacological Basis of
Therapeutics(10th Ed.), McGraw Hill, New Delhi, pp 321-333,337-343
1. Koda-Kimble Young (2000) Applied Therapeutics: The Clinical Use of
Drugs (7th Ed.), Lipincott Williams & Wilkins, Baltimore, pp 8.6-8.13