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

General Anaesthetic

Content

General anesthetics

•       Non-volatile anesthetics

•       Pharmacological actions of thiopental

•       Ketamine

•       Neuroleptanalgesia

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)

Uses

•       Anticonvulsant in emergency treatment of intractable seizures

•       Suitable drug for patients with cerebral oedema and brain tumor

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

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

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 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

–      Antiarrythmics

–      Anticonvulsants

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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