Introduction to anaesthetic lectures Flashcards
What is the maximum recommended safe dose of bupivacaine?
2mg/kg
What is the maximum recommended safe dose of lignocaine?
3mg/kg
What is the maximum recommended safe dose of prilocaine?
6mg/kg
What is meant by combination anaesthesia?
This is using a combination of drugs to achieve the desired effects:
Analgesia to reduce consciousness
Anaesthetic to reduce pain
Muscle relaxant to reduce muscle activity
Why is single agent analgesia problematic?
It typically requires large doses of a single agent which increases the risk of toxicity
Can lead to respiratory or cardiac depression
What are some key differences between anaesthesia and sleep?
Anesthesia don’t respond to pain
Anaesthesia don’t support your own airway
Anaesthesia don’t remove respiratory secretions, reduced swallowing
Don’t dream under analgesia
Analgesia you don’t move
How can general anaesthesia be induced?
IV or inhalational agent
Propofol is most commonly used
How is general anaesthesia maintained?
IV or inhalational agents
What are general anaesthetic agents often combined with?
Analgesia- typically opioid
Muscle relaxant- e.g. suxamethonium
Or they may be combined with a local anaesthetic
How does general anaesthesia differ from local anaesthesia?
Local anaesthetics prevent pain signals being generated at their source
General anaesthetics don’t prevent the pain signal being generated but reduce the central perception of pain
How do local anaesthetic agents work?
They exist in an ionised and non-ionised form. The non-ionised form is able to cross the cell membranes of neurons and the ionised form them blocks the voltage dependent sodium channels- preventing AP generation
Why is the use of LAs pH dependent?
The pH alters the proportion of ionised to un-ionised. There is a greater proportion of ionised LA in inflamed acidic tissue and this reduces the number of LA molecules that can cross the cell membrane, thereby reducing their effect.
What are the two types of bonds seen in LA agents?
Ester or Amide
Why does more pain result in greater LA effect?
The ionised form of the LA blocks the voltage gated sodium channels
There is greater opening of the sodium channels with greater pain signals and so greater blockage
Why don’t LA agents generally block motor fibres?
Motor fibres are much larger in diameter and are relatively resistant to the effects of LAs
Pain fibres are smaller in diameter and so are more prone the effects of LA.
What are some side effects of LAs?
Side effects develop with increasing plasma concentration
Lightheadedness, Tinnitus, Tongue numbness Visual disturbance Twitching Convulsions Unconsciousness Coma Respiratory arrest Arrhythmia and CV collapse
Name three local anaesthetic agents and give their maximum dose
Bupivacaine 2mg/kg
Lidocaine 3mg/kg
Prilocaine 6mg/kg
Give some methods of local anaesthesia
Topical- Creams, Spray
Infiltration- Injections into the target tissue
Regional nerve block- targeting a single nerve or plexus
Epidural- Into the epidural space
Spinal- LA injected into the subarachnoid space
IV Regional- Cuff used to reduce blood flow and IV anaesthetic give, very rarely done
What is often combined with LAs to reduce the systemic toxicity?
Adrenaline is used to cause vasoconstriction and reduce systemic uptake of the LA
This shouldn’t be done for toes and fingers as it could significantly reduce blood flow
What are some side effects of spinal/epidural anaesthesia?
Arrhythmia
Muscle paralysis
Urinary retention
Respiratory depression
Where is LA typically injected for an epidural?
Between L3 and L4
What kind of needle is used for an epidural?
A touhy needle is used
