What Is Anaesthesia Flashcards
Sleep vs anaesthesia
Sleep - respond to pain - move around - dream -maintain airway - may be partial closure snoring or transient closure OSA -Normal breathing -Swallowing normal -Sleep EEG Anaesthesia - no response to pain - no movement - no dream - lose airway - depressed ventilation -Reduced swallowing - anaesthesia EEG
Types of anaesthesia
Balanced - combination of different components that cause an anaesthetised state - anaesthesia to reduce consciousness, muscle relaxant that prevents movement - and analgesia that obtunds painful stimuli
Simple - just anaesthetic agent
The balanced anaesthesia approach reduces the side affects of anaesthetic agents by having multiple agents that target different needs to maintain during anaesthesia
Features or single agent anaesthetic
Simple - only one component
You need a larger amount of the drug so more likely to get cardiac or resp depression
Short procedures only
Features of balanced anaesthesia
Each component contributes to its affect
Side effects are reduced by the relatively smaller doses
Requires attention to detail
- too little anaesthetic agent = awareness
- to little analgesia = excess response to pain
- too little relaxant = unwanted movement
How is GA administered
Inhaled
IV
Induced and maintained
GA can be combined with Analgesics, relaxants, local or regional anaesthesia
What is sedation
Form of semi-hyponosis in which the patient is rousable, can talk but may have no memory of the events
Important they can maintain there airway
There is a concern that to much sedation a patient will no longer be able to do so
Types of anaesthesia
Local - topical or infiltration
RA- peripheral nerve block, ganglion/plexus block/ epidural, spinal, IV regional
GA - simple or balanced, inhalational - TIVA, TCI
How does the mechanism of GA work
GA prevents pain generated peripherally being interpreted as pain by the CNS
It does not stop the transmission of painful stimuli from the source of the pain
Mechanism on RA or LA
They prevent the transmission of a painful stimulus reaching the CNS
Chemistry of LA and how this affects their mechanism
Most have a lipid soluble hydrophobic aromatic group
And a charged hydrophilic aside group
Amide or Ester bond between groups
LA inhibit sodium influx through sodium voltage gated channels in the neuronal cell membrane
The molecule can exist in an unionised and ionised form
The pH determines which is the most predominant
PH is higher in the tissues so the molecule dissociates and the base enters the axon when inside the axon the pH is lower so re-ionisation takes place
The recognised portion enter the Na channels and blocks them preventing depolarisation
What happens when LA get into the plasma
1) they should not go into the plasma Increasing dose inc the severity of SE 4 - lightheaded, tinnitus 10 - convulsion 20 - resp arrest 26 - CV collapse
What is the max safe dose of bupivicaine
2mg/kg
What is the max safe dose of lignocaine
3mg/kg
What is the max safe dose of Prilocaine
6mg/kg
What topical application of LA are there
Eutectic mixture of LA (EMLA) lignocaine and prilocaine
Amethocaine cream/gel
Lignocaine spray
Benzocaine lozenges
What is local infiltration LA
Cannula, sutures
Field block - inguinal hernia
Wound infiltration - often with adrenaline
Why is adrenaline given with LA
Slows the systemic absorption of LA thus inc duration of LA effect and is useful in areas of inc vascularity where the risk of systemic absorption is higher
Adrenaline is CI in penile, digital block and around the nose and ear due to the risk of ischaemia
Where does spinal anaesthesia go
Into the subarachnoid space
L3-4
25-27G needle
What confirms the correct placement of needle in spinal anaesthesia
The flow of CSF back through the needle
What is epidural anaesthesia
Anaesthetic into the extradural space
Insert an indwelling catheter through a tuohy needle
Larger volumes on anaesthetic also opioids can be given this way
Thoracic lumbar and cervical can be given but need great skill
What is the name of the technique in epidural anaesthesia
Loss of resistance technique
Features of nerve blocks
LA injected close to the nerve Need to avoid vessels Up to 30mls required Single nerve Multiple - plexus of multiple nerve that supply an area such as an ankle block
What is IV regional anaesthesia known as in the wrist and how is it done
Biers block and is done in for a fractured wrist
The arm needs to be exsanguinated with a double tourniquet to prevent blood flow cuff up for >20 mins
Can be hazardous if cuff let down too soon - toxic effects of
LA in the circulation
What are the CI absolute and relative to LA
Consent unable
Surg unhappy with the conditions provided under LA
Absence operating too staff
Anticog coagulopathy
Infection at site of injection
Existing or suspected neurological deficit
