15 Local anaesthetics Flashcards
What are the three types of local anaesthesia?
Regional anaesthesia.
Local infiltration.
Topical.
What are the non pharmacological methods of local anaesthesia? (3).
Cold.
Pressure.
Hypoxia.
What are the non reversible pharmacological methods of anaesthesia? (4).
Phenol.
Ethanol.
Radio frequency.
Surgical.
Define local anaesthetic:
A drug that reversible prevents transmission of nerve impulses to the region to which it is supplied, without affecting consciousness.
Which layers does a local anaesthetic have to pass though? (3).
Epineurium.
Perineum.
Endoneurium.
How do local anaesthetics work?
Cross membrane as non-ionised form. Bind to intracellular surface of voltage gated sodium channels. Act as ionised form.
What is the structure of local anaesthetics?
Lipophilic aromatic residue.
Intermediate chain.
Hydrophilic amino group.
Differentiate between esters and amides.
Esters: COO group.
Amides: NHCO group.
How do you tell the difference between an ester and an amide?
Amides have an ‘i’ before the suffix ‘caine’.
What is pKa?
Clinical relevance?
pH at which ionised and non-ionised forms of LA are equal.
If pKa»_space; pH then onset of action is slower.
What is the pH of the body? Pus?
Body: 7.4
Pus: 6.9
What controls the duration of action of a local anaesthetic?
Protein binding. More binding = longer duration.
Dependant on intermediate chain length.
What does the potency of a local anaesthetic depend on?
Lipid solubility.
More soluble - more penetrates the membrane, less required for same effect.
What does the ability of a local anaesthetic to block nerve conduction depend on?
Type of nerve fibre (larger=slower).
Location - inside or outside the mantle.
In what order is sensory function lost with a local anaesthetic?
Col, warmth. First pain. Second pain. Touch, pressure. Motor function.
Why are vasoconstrictors used with local anaesthetics? (4).
Prolong action.
Reduced plasma levels: reduce CNS effects.
Reduce dose needed.
Reduce operative haemorrhage risk.
When are vast-constrictors not used with local anaesthetics?
In areas supplied by end arteries.
Penis, fingers and toes, ear lobules, ala of nose.
Which vasoconstrictors are used with local anaesthetics? (2).
Adrenaline.
Felypressin (no effect on heart).
In which type of local anaesthetic is hypersensitivity more of a problem?
Esters.
What is the main toxic side effect of prilocaine?
How does this occur?
Methaemoglobinaemia.
Metabolite 0- toluidine oxidises ferrous to ferric ions.
What are the symptoms of methaemoglobinaemia?
Treatment?
Cyanosis, lethargy, respiratory distress which doesn’t respond to oxygen.
IV methylene blue.
What order do the symptoms of local anaesthetic toxicity occur? (6).
Lightheadedness. Visual disturbances. Muscular twitching then convulsions. Unconsciousness then coma. Respiratory arrest. CVS depression.
How is local anaesthetic toxicity treated? (5).
Maintain airway. 100% oxygen. Control seizures. Cardiopulmonary resuscitation. Intravenous lipid emulsion.
Why is intravenous lipid emulsion the last line treatment for reversal of local anaesthetic toxicity?
May cause pancreatitis.
