2. GENERAL ANESTHESIA
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General anesthesia (GA) is the state produced
when a patient receives medications for amnesia,
analgesia, muscle relaxation, and sedation. An
anesthetized patient can be thought of as being
in a controlled, reversible state of
unconsciousness.
General anaesthetics
These pharmacological agent which are used to
produce reversible loss of consciousness is called
as general anaesthetics
4. PROPERTIES OF GENERAL
ANAESTHETICS
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It should be non toxic
It should be non irritaant
It should be non inflammable
It should be stable
It should be easy to administer
It should have proper muscle relaxant property
Should have adequate analgesic property
5. PREANESTHETIC MEDICATIONS
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Preanesthetic medications are defined as the use of
drugs or medications before or concurrent to the
administration of anesthetics to make anaesthesia safe
& pleasant
They are used to achieve following objectives like:
To reduce anxiety in patient occuring before & during surgery
To produce sedation, calm the patient & relieve pain
Counteract certain adverse effects of anaesthetics such as
salivation, vomitting etc.to reduce secretions
To reduce pre & post operative pain
To produce synergistic effect along with anaesthetics
facilitate smooth induction of anesthesia,
lowered the required dose ofanesthetic
There is no single drug which can achieve the above objective & hence
usually combination of drugs are useful
6. PREANESTHETIC MEDICATIONS:
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Analgesics eg. Paracetamol
Anxiolytics/ Tranquilizer eg. Diazepam, phenobarbitone
Anticholinergics: eg. Atropine, scopolamine
(Reduces bronchial and salivary secretion)
Skeletal muscle relaxants: eg. D- tubocurarine
Antiemetics: eg. Promethazine
Prevents aspiration of stomach contents and post surgical vomiting
7. DEPTH OF ANESTHESIA (GUEDEL’SSIGNS)
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Guedel (1920) described four sequential stages with anaesthesia, dividing the
stage into 4 planes.
Stage of
Analgesia
• analgesia and amnesia, the patient is conscious and
conversational. Starts from beginning of anaesthetic inhalation
and lasts upto the loss of consciousness
• Pain is progressively abolished
• Reflexes and respiration remain normal
• Use is limited to short procedures
Stage of
Delirium
• From loss of consciousness to beginning of regular respiration
• Patient may shout, struggle and hold his breath; muscle tone
increases, jaws are tightly closed, breathing is jerky; vomiting,
involuntary micturition or defecation may occur
• Heart rate and BP may rise and pupils dilate due to
sympathetic stimulation
• No operative procedure carried out
• Can be cut short by rapid induction, premedication
8. DEPTH OF ANESTHESIA (GUEDEL’SSIGNS)
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Surgical
anaesthesia
• Extends from onset of regular respiration to cessation of
spontaneous breathing. This has been divided into 4 planes
which may be distinguished as:
• Plane 1 moving eye balls. This plane ends when eyes become
fixed.
• Plane 2 loss of corneal and laryngeal reflexes.
• Plane 3 pupil starts dilating and light reflex is lost.
• Plane 4 Intercostal paralysis, shallow abdominal respiration,
dilated pupil.
Medullary
paralysis • Cessation of breathing to failure of circulation and death.
9.
10. MECHANISMOFACTIONOFANAESTHESIA
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No specific receptor has been identified. The fact that
chemically unrelated compounds produce anesthesia argues
against the existence of a single receptor.
The focus is NOW on proteins comprising ion channels:
GABAAreceptors, Glycine receptors,
NMDAglutamate receptors (nitrous oxide and ketamine ):
Nicotinic receptors: Blocks the excitatory postsynaptic current
of the nicotinic receptors.
11. MECHANISM OF ACTION OF
GENERAL ANAESTHETICS
GABA –A receptor : Potentiated by
Halothane,
Propofol, Etomidate ,Enflurane,
isoflurane, Desflurane,
sevoflurane
NMDA receptors:
Glycine receptors :
Inhibited by Ketamine,
nitrous oxide and xenon
Potentiated by Halothane,
Propofol, ,Enflurane,
isoflurane, Desflurane,
sevoflurane
Also has effect on neuronal nicotinic receptorsand
5-HT3 receptors
12. INHALATIONAL
ANAESTHETICS
Inhalational anaesthesia refers to the delivery of gases or
vapours to the respiratory system to produce anaesthesia
Ether
It is explosive
Irritant to respiratory tract
High incidence of nausea and vomiting during
induction and post-surgical emergence
13. Colourless, odourless gas at room temperature.
Very insoluble in blood and other tissues (quick recovery)
Rapid induction of anaesthesia and rapid emergence
following discontinuation of administration.
Completely eliminated by the lungs.
It is weak anaesthetic and powerful analgesic.
The mac value is 105%.
Causes megaloblastic anaemia.
Used as adjunct to supplement other inhalationals.
NITROUS OXIDE
14. Volatile liquid at room temperature.
Light sensitive
High fat solubility => slow induction & recovery
Eliminated unchange via lungs
Commonly used in children, where preoperative
placement of an iv catheter can be difficult
It is marketed in amber bottles with thymol added as a
preservative
Metabolised in liver by Cyt-P450
HALOTHANE
15. Side effects of halothane :
CVS : Cardiac arrhythmia, depression of myocardial contraction.
Respiratory system : Depression of respiration
Muscles : Malignant hyperthermia
Kidney : Decrease renal blood flow and g.f.r
Liver and GIT: Cause halothane induced hepatitis & nausia and
vomitting
DRUG INTERACTION : Halothane + adrenaline, theophylline => arrhythmia
may be precipitated.
CONTRAINDICATION : Hepatic dysfunction and/or jaundice.
16. INTRAVENOUS ANAESTHETICS
THIOPENTAL
Ultrashort acting barbiturate
High lipid solubility rapid entry into the brain
Rapid onset (20 sec) , short duration
Effect terminated not by metabolism but by redistribution
Risk of sever vasospasm if accidently injected intoartery
Depress cerebral blood flow
Decrease intracranial pressure
Tissue necrosis—gangrene, Tissue stores, hypotension, apnea
Build-up in adipose tissue = very long emergence fromanaesthesia
17. Rapid onset and have a short duration of action
Highly protein bound in vivo and is metabolised by conjugation
in the liver
Very good anesthetic for induction and maintaince of anesthesia
with no accumulation effect
Side-effects are pain on injection, hypotension and transient
apnea following induction
Used for the induction, maintenance of GA andsedation
Useful for day-case surgery
PROPOFOL
18. Dissociative anaesthetic
NMDA ReceptorAntagonist
Cardiovascular stimulant
Catatonia, analgesia, and amnesia without loss of consciousness
Useful for anesthetizing patients at risk for hypotension and
bronchospasm and for certain paediatric procedures
KETAMINE
19. Rapid induction
Minimal change in cardiac function and respiratory rate
Not analgesic
Cause pain on injection and nausea postoperatively
Prolonged administration may cause adrenal suppression
ETOMIDATE