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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