PHARMACOLOGY – I (PRACTICAL)[PHL 313]

DR. MOHD NAZAM ANSARI

Background General anesthesia was absent until the

mid-1800’s William Morton administered ether to a

patient having a neck tumor, removed at the Massachusetts General Hospital, Boston, in October 1846.

The discovery of the diethyl ether as general anesthesia was the result of a search for means of eliminating a patient’s pain perception and responses to painful stimuli.

Lab 3:STUDY OF DIFFERENT

STAGES OF ANESTHESIA

Partial or complete loss of sensation with or with out loss of consciousness as a result of disease, injury, or administration of an anesthetic agent, usually by injection or inhalation.

Anesthesia

TYPES OF ANESTHESIA

A. GENERAL- A drug that brings about a reversible loss of

consciousness Total loss of consciousness and sensation,

sleep (unconsciousness), and muscle relaxation;

IV, Inhalation, Rectal

B. LOCAL- Reduce all painful sensation in one region of

the body without inducing unconsciousness.

INHALATION ANESTHETIC AGENTS

Volatile Liquids Ether Halothane ( Fluothane) Enflurane (Ethrane) Isoflurane (Forane) Sevoflurane (Ultrane) Desflurane ( Suprane)

Gases Nitrous oxide Cyclopropane Ethylene

INTRAVENOUS ANESTHETIC AGENTS

Inducing Agent (~11 sec) Thiopentone sodium Propofol Etomidate

Slower Acting Drugs Benzodiazepines

Diazepam (5-10 min) Lorazepam

Dissociative anesthesia Ketamine

Neurolept analgesia Fentanyl + Droperidol

LOCAL ANESTHESIA Rectal (Pediatrics)-

Anectine, Pentothal Na 5-10%

Spinal anesthesia- Procaine (Novocaine), Tetracaine(Pontocaine), Lidocaine(Xylocaine), Mepivacaine (Carbocaine), Bupivacaine( Marcaine)

Muscle relaxants- Anectine (Succinyl choline), Pavulon (Pancuronium)

Description General Anesthetics Local Anesthetics

1. Site of action Central Nervous System Peripheral Nerves

2.Area of body involved Whole body Restricted area

3. Conciousness Lost Unaltered

4. Major surgery Preferred Can not be used

5. Minor surgery Can not be used Preferred

6. Poor health patient Risky Safer

7. Care of vital function Essential Usually not needed

Anesthesiology

Preanesthetic medication:It is the use of drugs prior to anesthesia to

make it more safe and pleasant. To relieve anxiety – benzodiazepines. To prevent allergic reactions –

antihistaminics. To prevent nausea and vomiting –

antiemetics. To provide analgesia – opioids. To prevent bradycardia and secretion –

atropine.

Lipid theory of General Anaesthetics

Based on the fact the anesthetic action is correlated with the oil/gas coefficients.

Higher the solubility of general anesthetics in oil greater is the anesthetics action.

Anesthetic Suppression of Physiological Response to

Surgery

Anesthesiology

Molecular mechanism of the GA : GABA –A : Potentiation by

Halothane, Propofol, Etomidate NMDA receptors : inhibited by

Ketamine

Molecular Actions: GABAA

Receptor Ligand-gated ion channels

Chloride channels gated by the inhibitory GABAA receptor

GABAA receptor mediates the effects of gamma-amino butyric acid (GABA), the major inhibitory neurotransmitter in the brain

GABAA receptor found throughout the CNS

Most abundant, fast inhibitory, ligand-gated ion channel in the mammalian brain

Located in the post-synaptic membrane

Molecular Actions: GABAA

Receptor GABAA receptor is a 4-transmembrane (4-

TM) ion channel 5 subunits arranged around a central

pore: 2 alpha, 2 beta, 1 gamma Each subunit has N-terminal

extracellular chain which contains the ligand-binding site

Molecular Action: GABAA

Receptor

Molecular Action: GABAA

Receptor Receptor sits in the membrane of its neuron at the synapse

GABA, endogenous compound, causes GABA to open

Receptor capable of binding 2 GABA molecules, between an alpha and beta subunit Binding of GABA causes

a conformational change in receptor Opens central pore Chloride ions pass

down electrochemical gradient

Net inhibitory effect, reducing activity of the neuron

STAGES OF ANESTHESIA Irregular descending depression of CNS

STAGE 1 (ANALGESIA/ONSET/INDUCTION): Extends from the administration of anesthesia

to the time of loss of consciousness. Pain is progressively abolished during this

stage. Patient remains conscious, can hear and see,

and feels a dream like state. Reflexes and respiration remain normal. Some minor and major operation can be

carried out.

STAGE 2 (EXCITEMENT/DELIRIUM): Extends from the time of loss of consciousness

to beginning of regular respiration Characterized by struggling, delirium, irregular

respiration, and breatholding are commonly seen.

Muscle tone increases, jaws are tightly closed, vomiting, involuntary micturation or defecation may occur.

Heart rate and BP may rise. Pupils are dilated. No operation.

STAGE 3 (Surgical Anesthesia): Extends from the regular respiration to the

loss of most of the reflexes. Muscle tone decreases, BP falls, HR increases,

constricted pupils, and regular respirations. Surgical procedure is started.

STAGE 4 (Impending Death/ Stage of Danger): Cessation of breathing, to failure of circulation

and death. Pupil is widely dilated. It is due to anesthesia overdose.

Thank you