General Anaesthetic - Pharmacology B. Pharma 5th Semester PDF Notes

General Anaesthetic


General anesthetics

       Non-volatile anesthetics

       Pharmacological actions of thiopental



Intended Learning Outcomes

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

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

Reduce cerebral metabolic rate of O2 consumption


Cerebral vasoconstriction


Reduce intracranial pressure and blood flow

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


       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

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

       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

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

       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


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

       Differs from the classical general anesthesia

       Subject is conscious and able to cooperate during operative procedure

       Most favoured combination: Neuroleptic droperidol and analgesic drug  fentanyl

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

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 aspirational pneumonia

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




       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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