L19 Local Anaesthetics Flashcards
Name three common local anaesthetics used nowadays
Lignocaine, bupivacaine and ropivacaine
Explain the significance of knowing the pKa of a local anaesthesia
All the local anaesthesia are weak base, meaning they exist as two forms, the ionised and unionised. In acidic medium, more will appear as pronated form, hence moving to the left side of the graph. Local anaesthetics can only diffuse into the cell in a free base form. In acidc medium, it tends to act less satisfactorily. If it is an inflamed area, the local anaesthetic tends to act less well. Sodium bicarbonate solution can be used to make it more alkaline and it spends up the local anaesthetic block.
Routes of administration of local anaesthesia
Tropical Infiltration Nerve/ plexus Epidural/ spinal Intravenous
Name the occasion where local anaesthesia is applied tropically
Usually work on throats or eyes
What is the clinical significance of ELMA (Eutectic mixture local anaesthetic)
It can be used at a higher concentration
Name the occasion where epidural route is used for administration
Per labour injection
If you can find a lump of nerves, you can inject that and this can be highly effective
Name the occasion where intravenous route is used for administration of local anaesthetics
Bier’s block
uses the tourniquet to tie off the circulation of the arm, hence preventing the local anaesthetic from entering the systemic circulation
Name the dose limit for lignocaine
4mg/kg
7mg/kg (with adrenaline)
Name the rationale for adding adrenaline with local anaesthetic
Adreanline causes vasoconstriction, which reduces the absorption of local anaesthetic into the circulation
What is the dose limit of bupivacaine
2.5mg/kg
When is the use of adrenaline avoided?
Penile nerve block
Digital artery
What does 1% mean?
10mg/ml
What does 1:200,000 indicate?
5microgram/ ml
When comparing size, which is the harder to block?
Larger ones
List the side effects of LA
Motor block
Sympathetic block
Metabolites
Allergy
