Sem 3, case 10 (general anaesthetic) Flashcards
What are the 2 drugs used in induction of general anaesthetic
Propofol
Isoflurane
How is propofol administered?
IV injection
What are the pros and cons to IV induction (propofol)?
Pros:
- rapid onset (3 secs)
- reduced number of complications
- misses excitatory phase
Cons:
- might not be easy to find the vein on some patients
What are the pros and cons of inhalation induction (isoflurane)?
Pros:
- easier in difficult to obtain IV patients
- easier to use in paediatrics
- easier patients with airway difficulty
Cons:
- slower onset (7 mins)
Which neurotransmitter do induction agents interact most with?
GABA
(via GABA-A receptor)
What is the MOA of propofol?
Positive modulation of GABA inhibition via GABA-A receptor
= Increase GABA interaction with the GABA-A receptor = more inhibition of action potentials
What is the MOA of isoflurane?
Binds to receptors:
- GABA
- NMDA
- Glycine
(Full MOA unknown)
What are the side effects of propofol ?
Hypotension
Respiratory depression
Brady cardia
Nausea + vomiting
Adrenocortical suppression
What are the side effects of isoflurane?
Hypotension
Respiratory depression
vasodilation (coronary)
What are the main aspects of maintenance?
Maintaining:
- unconsciousness
- analgesia
- muscle relaxation
- airways
How is unconsciousness maintained during general anaesthesia?
Continue administering the drug used in induction (propofol or isoflurane)
How are airways maintained during general anaesthesia?
Usually:
- endotracheal tube (ET) = tube inserted past vocal cords
- tracheostomy tube = tube inserted at level of 2nd tracheal ring, passes vocal cords
- supraglottic airway (SGA) = tube inserted that sits on/in vocal cords
ventilate with O2 and Nitrous Oxide (NO)
How is muscle relaxation maintained during general anaesthesia?
Using Ach antagonists
- atracurium
- suxamethonium
How is atracurium administered?
IV injection
How is suxamethonium administered?
IV injection
What is the MOA of atracurium?
Ach antagonist at the motor end plate (NMJ) = competitive inhibitor
= NON-DEPOLARISING agent
What is the MOA of suxamethonium?
Ach agonist (acetylcholinesterase resistant)
- mimics Ach but takes way longer to hydrolyse
- stays in NMJ receptors for longer, prolonging depolarisation
= neuromuscular blockade
= DEPOLARISING agent
How does atracurium leave circulation?
Spontaneously hydrolyses in plasma
How does suxamethonium leave circulation?
Hydrolysed by acetylcholinesterase rapidly after withdrawal
What are the side effects of atracurium?
Hypotension
Bronchospasm
Ganglion block
What are the side effects of suxamethonium?
Bradycardia
Hyperkalaemia
Increased intraocular pressure
Postoperative pain
(Same as glycopyrrolate)
How is analgesia maintained during general anaesthesia?
Fentanyl = Opioid analgesic
How quickly do induction agents ware off if not replenished?
After 5-10 minutes
How is unconsciousness reversed in the process of general anaesthesia?
Stop giving the induction agents (propofol or isoflurane)
How is muscle relaxation reversed in the process of general anaesthesia?
Administer neostigmine and glycopyrrolate
How is neostigmine administered?
IV injection
(Or intramuscular injection/subcutaneous injection)
How is glycopyrrolate administered?
IV injection
(Or intramuscular injection/orally/topically)
What is the MOA of neostigmine?
Reverses non-depolarising muscle relaxants (e.g atracurium)
- blocks acetylcholinesterase
= increases Ach in NMJ
= increases muscle contraction
Which drug must be administered alongside neostigmine?
Glycopyrrolate
Why does glycopyrrolate need to accompany neostigmine?
Limits the parasympathomimetic side effects of neostigmine
(Parasympathomimetic drug = activates parasymp NS by mimicking/modifying Ach action)
What are the side effects of neostigmine?
Hypotension
Bradycardia
Bronchoconstriction
Muscular fasiculations
What is the MOA of glycopyrrolate?
Muscarinic receptor ANTagonist
= inhibits Ach transmission
Which drugs in general anaesthesia can cross the BBB?
Induction agents (propofol, isoflurane)
Atracurium metabolites (muscle relaxant)
Atropine (a less potent alternative to glycopyrrolate, as that cannot cross BBB)
What are the side effects of glycopyrrolate?
Bradycardia
Hyperkalaemia
Increased intraocular pressure
Postoperative pain
(Same as suxamethonium)
What are the 2 main drugs used in induction?
Propofol (IV)
Isoflurane (inhalation)
What are the 2 main drugs used as muscle relaxants?
Atracurium
Suxamethonium
What are the 2 main drugs used in reversal of general anaesthesia?
Neostigmine
Glycopyrrolate
What are the most common drugs used as for analgesia in general anaesthesia?
Opioids
- fentanyl
- morphine
- hydromorphone
What are some of the premeds used before general anaesthesia? What do they do?
- benzodiazepines (sedation and amnesia)
- opioids (analgesia and sedation)
- anticholinergics (antiemetic = stops vomiting)
- antibiotics (infection prophylaxis)
Which drug does not get reversed by simply stopping administration?
Atracurium
(use neostigmine and glycopyrrolate)
What is some info needed before commencing general anaesthesia?
- Age
- consent
- BMI
- airway inspection for intubation
- PMHx
- administer pre-meds
