General Anaesthetic PDF / PPT

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Course Code: PCS 3203
Course Title: Pharmacology II 1


Lecture No 12
General Anaesthetic

At the end of this lecture, student will be able to

• Give examples for non volatile anaesthetics/intravenous


• Explain the pharmacological actions of thiopental

• List the uses of ketamine

• Describe neuroleptanalgesis 2



General anesthetics

• Non volatile anesthetics

• Pharmacological actions of thiopental

• Ketamine

• Neuroleptanalgesia 3


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 4


Intravenous anaesthetics- thiopental

Reduce cerebral metabolic rate of O2 consumption

Cerebral vasoconstriction

Reduce intracranial pressure and blood flow 5


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)


• Anticonvulsant in emergency treatment of intractable seizures

• Suitable drug for patients with cerebral oedema and brain tumor 6


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 7


Thiopental – ADME 8


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 9



• 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 10


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 11



• Used for short lasting procedure:

– Cardiac catheterization, bronchoscopy, dressing of burns, forceps

delivery, teeth extraction, manual removal of placenta, dental


• Not used in:

– Heart disease, abdominal surgery, thyrotoxic patients, pregnant

women at term, operation of eye, psychiatric disorders 12



• Combines the use of a neuroleptic drug with an opioid analgesic


• Differs from the classical general anesthesia

• Subject is conscious and able to co operate during operative


• Most favoured combination: Neuroleptic droperidol and analgesic

drug fentanyl 13


Preanesthetic Medication

• To reduce anxiety and apprehension

• To obtain additive or synergistic effect – induction smooth and


• To counteract certain adverse effects

• To relieve pre and post operative pain

• To suppress respiratory secretion

• To reduce reflex excitability 14


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


5. H2 Blockers/PPIs: reduce the risk of gastric regurgitation and

aspirational 15


Drugs Administered During Anesthesia

• Skeletal muscle relaxant

• Very short acting ganglionic blocker – to produce controlled


• Drugs to counter the anesthetic complication:

– Vasopressin – to correct hypotension

– Antiarrythmics

– Anticonvulsants 16



• 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


• Following single dose produces dissociative anesthesia 17


Thank You