Course Code: PCS 3203
Course Title: Pharmacology II
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Lecture No 12
General Anaesthetic
At the end of this lecture, student will be able to
• Give examples for non volatile anaesthetics/intravenous
anaesthetics
• Explain the pharmacological actions of thiopental
• List the uses of ketamine
• Describe neuroleptanalgesis
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Content
General anesthetics
• Non volatile anesthetics
• Pharmacological actions of thiopental
• Ketamine
• Neuroleptanalgesia
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Intravenous anaesthetics
• These are inducing agents- because of rapidity of onset of action
• Maintained by inhalation agent
• Fast inducers- thiopental, methohexital, etomidate and propofol
Thiopentone sodium
• Ultra short acting barbiturates
• Induction very quick and pleasant- recovery also rapid
• Rapidly cross BBB and diffuse rapidly out of brain and redistributed
• Short acting
• Poor analgesic
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Intravenous anaesthetics- thiopental
Reduce cerebral metabolic rate of O2 consumption
Cerebral vasoconstriction
Reduce intracranial pressure and blood flow
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Thiopental – Anesthetic Action
Adverse effects
• Laryngospasm- prevent by atropine and succinylcholine
• Postoperative Pain – adequate analgesia should be provided
• pH is 11- local tissue damage(extravasate)
Uses
• Anticonvulsant in emergency treatment of intractable seizures
• Suitable drug for patients with cerebral oedema and brain tumor
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Thiopental – ADME
• High lipid solubility
• Very short duration of action
• Rapidly metabolized by liver
• With successive doses body fat depots get saturated
• Slow release into plasma – prolonged recovery
• Readily cross placental barrier
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Thiopental – ADME
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Ketamine- Dissociative anaesthesia
• Characterised by a feeling of dissociation from surrounding.
Profound analgesia, immobility and amnesia
• Primary site of action- cortex and limbic system (not RAS)
• Block the action of glutamate at NMDA receptor
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Ketamine
• Dose: IM 5-10 mg/kg, IV 1-2 mg/kg
• 0.1 – 0.25 mg/kg IV complete analgesia
• Increases BP, HR, CO – Avoided in IHD patients
• Suitable for patients of hypovolemic shock
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Disadvantages of Ketamine
• Causes Nystagmus, involuntary movements
• May cause delirium, hallucinations, colourful dreams
• Salivation may be troublesome
• Muscle relaxation – inadequate
• Increases i.o.t and intracranial pressure
• Drug of abuse
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Ketamine
• Used for short lasting procedure:
– Cardiac catheterization, bronchoscopy, dressing of burns, forceps
delivery, teeth extraction, manual removal of placenta, dental
work
• Not used in:
– Heart disease, abdominal surgery, thyrotoxic patients, pregnant
women at term, operation of eye, psychiatric disorders
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Neuroleptanalgesia
• Combines the use of a neuroleptic drug with an opioid analgesic
drug
• Differs from the classical general anesthesia
• Subject is conscious and able to co operate during operative
procedure
• Most favoured combination: Neuroleptic droperidol and analgesic
drug fentanyl
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Preanesthetic Medication
• To reduce anxiety and apprehension
• To obtain additive or synergistic effect – induction smooth and
rapid
• To counteract certain adverse effects
• To relieve pre and post operative pain
• To suppress respiratory secretion
• To reduce reflex excitability
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Preanesthetic Medication
1. Opioid analgesics
2. Sedative and tranqullisers: Bzds like diazepam/lorazepam: -smooth
induction, loss of recall of perioperative events
3. Antimuscarinic drugs: Atropine/hyoscine and glycopyrrolate to
reduce salivary and bronchial secretion
4. Antiemetics: Metoclopromide reduce post operative vomiting,
reduce chances of reflux and aspiration( by increase gastric
emptying)
5. H2 Blockers/PPIs: reduce the risk of gastric regurgitation and
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Drugs Administered During Anesthesia
• Skeletal muscle relaxant
• Very short acting ganglionic blocker – to produce controlled
hypotension
• Drugs to counter the anesthetic complication:
– Vasopressin – to correct hypotension
– Antiarrythmics
– Anticonvulsants
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Summary
• Thiopental has high lipid solubility and thereby very short duration
of action
• It is used in induction of anesthesia in short duration for fracture
reduction, dilatation and curettage, laryngoscopy, bronchoscopy
• Ketamine is antagonist at NMDA receptor of cerebral cortex (limbic
system)
• Following single dose produces dissociative anesthesia
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Thank You
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