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General Anaesthesia - Intravenous Anaesthesia (NMDA-glutamate receptor…
General Anaesthesia - Intravenous Anaesthesia
Ultra-short acting barbiturates
-
thiopentone
:star: -
methohexitone
:check:
Highly lipophilic
Rapid
onset of action as they cross BBB rapidly
Short
duration of action
due to
redistribution
into adipose tissues and muscles
Get metabolise
slowly
and
long
elimination
Due to accumulation in body fat
No analgesia
:!!:
Narrow therapeutic index
:!!:
Cause severe vasopasm if injected into artery
NMDA-glutamate receptor antagonist
-
Ketamine
:<3: -
Althesin
:explode:
Very rapid
onset of action (30 sec)
Short
duration of action (up to 30 minutes)
for minor surgery
Acts on cerebral cortex and limbic system
No cardiovascular depression
Produce dissociative anaesthesia
:!!:
Side effects
Unpleasant dream among adults
Give along with benzodiazepines
Mainly useful for
children
Althesin
:explode:
Steroid
derivative
No tissue necrosis when giving IV
Hypersensitivity
-due to cremaphor solvent
Etomidate
:recycle:
Rapid
onset and
short
duration of action
for anaesthetic
induction
among patient with risk of
hypotension
Suppress
adrenocorticol function - low cortisol production
Cause
pain
and
extraneous muscle movements
reduced by premedication of benzodiazepines or opioids
Safe to use in patients with CVS complication
Propofol
:champagne:
Rapid
recovery and metabolism
Side effects
Respiratory depression
Hypotension
Use in
ophthalmic surgery
as it can reduce intraocular pressure
Short-acting benzodiazepines
(use at high dose) -
Midazolam
: :pen:
Slow
onset of action and
slow recovery
(i.e.
long
duration of action)
Used along with
ketamine
:<3: as
basal anaesthesia
water-soluble
diazepam
is :checkered_flag: not water-soluble- cause pain when IV
Basal anaesthesia
:black_flag:
Purposes
Induce
semi-consciousness
to
reduce anxiety
:smiley:
Make
induction easier
Modify
depth of anaesthesia
rapidly
Agents
Thiopentone :star: IV or rectal paste
Diazepam :checkered_flag: large IV
Ketamine :<3: - induce
dissociative anaesthesia
Paraldehyde :lock: - rectal
Neuroleptanalgesia
:question:
Purposes
Immobilization, devoid of pain, sedated, amnesic but
not unconscious
Obey commands and answer simple questions
burns dressing
diagnosis - cystoscopy, bronchoscopy
when unconsciousness is inadvisable
Agents
50:1 Droperidol (neuroleptic) and fentanyl (opioids)
Tranquilizer -
3:1 diazepam and pentazocine
Supplement with
nitrous oxide
Adjuncts
Pre-medication
depends on nature of surgery
opioids
morphine,pethidine,pentazocine
analgesia, sedation, reduce anxiety
given
before barbiturate induction
- can lower dose of barbiturate needed
sedatives and anxiolytics
reduce anxiety,
induce amnesia
Reduce circulating catecholamines - avoid high BP
Reduce risk of cardiac arrhythmias
Benzodiazepines
anti-cholinergics
atropine,hyoscine
reduce bronchial and salivary secretions
prevent excessive bradycardia and hypotension
hyoscine also can used as
hypnotics
Neuroleptics
chlorpromazine,droperidol,haloperidol
used as sedatives
synergise
with anaesthetics
anti-emetic
metoclopramide
:silhouette:
increase gastric emptying
anti-emetic
During surgery
Depolarizing muscle relaxant
Suxamethonium
destroyed by
pseudocholinesterase
Anticholinesterase do not reverse the action :!!:
Rapid
paralysis but
short
duration of action (i.e. fast recovery)
Paralyze
larynx and pharynx
Non-depolarizing muscle relaxant
vecuronium,atracurium
Slower
onset but
long
paralysis (i.e. slow recovery)
Can be reversed with
anticholinesterase
Hydrolysis of acetylcholine is inhibited , hence compete with non-depolarizing muscle relaxant at the receptor site
Pressor drugs
adrenaline, metraminol,dopamine, dobutamine
maintain blood pressure
Depressor drugs
trimetaphan, sodium nitroprusside
lowering blood pressure -
reduce excessive bleeding
Post-operation
Anticholinesterase
edrophonium, neostigmine (+atropine - to counter excess acetylcholine)
Reverse effects of non-depolarising muscle relaxant
Ensure patent airway and adequate ventilation
Respiratory stimulants
Naloxone, doxapram
Reverse
opioid
-induce respiratory depression
Analgesic
opioids
Sedatives and anxiolytics
diazepam
Muscarinic agonist
to overcome excess effect of atropine