Local Anaesthetics Flashcards
Pharmacological ways of stopping pain - non-reversible
Phenol
Ethanol
Radiofrequency
Surgical
Reversible pharmacological ways of stopping pain
Local anaesthetics
Where are local anaesthetics injected? what does this mean for its movement in the body?
Around a nerve
Has to pass through epi->peri->endoneurium then through the nerves in the nerve fibre to reach central axons- takes time to act
Mode of action of local anaesthetics
- LA crosses membrane
2. binds intracellularly to Na channel
Crossing the membrane requires what of LA? Why is this a problem?
Them to be uncharged
Problem as only binds when ionised
Local anaesthetics bind to what subunit in an Na channel?
Alpha subunit
3 constituent parts of cocaine molecule
Lipophilic
Intermediate chain
Hydrophilic
Types of cocaine
Amides or esters
Looking at general names between amides and esters
i is included before -caine in amides
pKa wants to equal pH - why?
Ionised and non-ionised forms of local anaesthetics are equal
Quicker onset
Sensory function lost in what order
Cold, warmth
Pain (Aa fibres, then second pair of C fibres)
Touch, deep pressure
Motor function
What are often added to LAs?
Vasoconstrictors
Why vasoconstrictors?
Prolong action
Reduce plasma levels
Reduced dose of anaesthesia
Reduced operative haemorrhage
When not to add vasoconstrictors?
To areas supplied by end vessels
Fingers&toes, penis, ear lobule, ala of nose
Which vasoconstrictors are used?
Adrenaline
Felypression - less effective but not effect on heart conduction/contraction
Lipid solubility determines what
Potency of LA
Adverse effects of LAs
Hypersensitivity - anaphylaxis, more common in esters, may be rxn to preservatives
Methaemoglobinaemia - prilocaine problem, metabolised 0-toluidine which oxidises ferrous to ferric ions, stops O2 binding, cyanosis, lethargy, resp distress which is not responsive to oxygen
Treatment of methaemoglobinaemia
IV Methylene blue 1.5mg/kg
LA toxicity affects what first
Highly sensitive areas of body e.g. eyes, face, ears
Moves to inhibitory parts of brain producing twitches
LA toxicity progression of symptoms
Lightheaded, tinnitus, circumoral and tongue numbness
Visual disturbances Muscular twitching Convulsions Unconsciousness Coma Resp arrest CVS depression
Treatment of LA toxicity
Stop injecting
Call for help
A: maintain airway, maybe secure with traceal tube
B: give 100% O2 and ensure lung ventilation
C: Confirm of establish IV access
D: control seizures
Draw blood for analysis
Assess CVS function
Start cardiopulmonary resus
Give IV lipid emulsion
