Transcript Local Anaesthetic Toxicity

Local Anaesthetic Toxicity
John Kilic
28th October 2005
Mode of action
Factors affecting toxicity
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Absorption
Distribution
Metabolism
Protein binding
Placental transfer
Absorption
Sites and rates
Fastest
• Intercostal space
• Epidural space
• Brachial plexus
• Lower limb blocks
Slowest
• Local infiltration
Distribution
Other factors
• Metabolism
• Amidases in liver
• Proportional to hepatic flow
• Protein
binding
• Values don’t correlate with toxicity acurately
• Placental
transfer
•  total protein [LA] / same free [LA]
•  rate hepatic metabolism in foetus
• no significant problems with toxicity as long as
episode not close prior to delivery
Common Las and toxic doses
Lignocaine
Lignocaine with adrenaline
Bupivocaine
Ropivocaine
Prilocaine
Prilocaine with felypressin
Cocaine
3 mg/kg
7 mg/kg
2 mg/kg
3 mg/kg
6 mg/kg
8 mg/kg
3 mg/kg
Symptoms - CVS
 rate phase IV depolarisation
 duration action potential
 effective refactory period
 conduction velocity
slight in SVR (slight in BP)
• Low dose
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• High dose
•  SVR
•  myocardial contractility
• possible cardiovascular collapse due to these
Symptoms - CNS
• Low doses
Inhibitory pathway
• High doses
Inhibitory + facilitatory pathways
• Intra-arterial
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Lightheadedness
Dizziness
Visual/auditory hallucinations
Seizures
• Drowsiness
• Disorientation
• Coma
• LA/neurotransmitter/receptor
complex formed
• Neuromuscular blockade
Symptoms - Other
• GI
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• Metabolic
• some anticholinergic activity
• some antihistamine activity
contraction of intact bowel
Risk of anaphylaxis with LAs very rare
Treatment
• Stop injection/infusion
• ABC !!
• Treat initial Sx with O2
• Repeated doses midazolam (1-4mg)
Treatment (cont)
• Modsevere
• Drug OD in presence of hypoxia
• Prevent convulsions
• Maintain oxygenation
• GCS/
convulsions
• Intubate
• Preferentially sux/thiopentone
• Ventilate 100% O2
• CV collapse
• Commence CPR
Methaemoglobin
• Hepatic metabolism prilocaine produces otoluidine
• o-toluidine oxidises Hb to methaemoglobin
• Especially doses >600mg prilocaine
• Avoid prilocaine in anaemia/pregnancy
• Treatment with 1mg/kg methylene blue
Prevention of toxicity
AVOID INTRAVASCULAR INJECTION!!!!!
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Repeat careful aspiration
Use adrenaline 1:200,000/vasoconstrictor
Care with site of injection
Care with patient’s general condition
Care with dose used
Any questions?