Local Anaesthetic Toxicity (AAGBI)

Question 1

LAST Incidence

Answer 1

1.8 per 1000 Nerve Blocks
Most common causative agent lidocaine
50% of events occur within 10mins of injection

Question 2

LAST Emergency Management

Answer 2

• Stop injecting LA
• Call for help, cardiac arrest trolley and lipid emulsion pack
• ABCDE

Intralipid
- 20% intralipid bolus 1.5ml/kg over 2-3mins
- Start an infusion of 15ml/kg/hour
- If no improvement then further bolus dose then double the rate of the infusion
- Max cumulative dose 12ml/kg

If circulatory arrest differences to ALS:
- Smaller dose of adrenaline (1mcg/kg) (increases afterload and interferes with intralipid)
- Avoid vasopressin (Worse outcomes in LAST, reduced CO)
- Be aware recovery can take >1 hour
- Consider ECMO

If seizures:
- Small incremental boluses of IV benzodiazepines

Question 3

Pathophysiology of LAST

Answer 3

• LA is likely to be involved in disrupting normal mitochondrial aerobic respiration
• As the heart and brain are highly intolerant to anaerobic respiration symptoms develop here quickly
• Direct ionotropic and metabotropic disruption caused by Na channel inhibition also plays a significant role

Question 4

Mechanism of action of intralipid

Answer 4

• Directly ionotropic
• Cardioprotective of reperfusion injury
• Acts as a “lipid sink” partitions the positively charged lipophilic local anaesthetic inside negatively charged fat molecules and redistributes these to the muscle and liver

Question 5

Follow up following LAST

Answer 5

• Careful observation for at least 6 hours as LA can redistribute
• If the diangosis is clear and there has been no cardiovascular compromise then elective surgery may be acceptable to continue following an observation window of 30-40mins

Question 6

Risk Factors for LAST

Answer 6

LA RFx
- Type of LA
- Volume and rate of injection
- Where the LA was injected

Patient RFx
- Pre-existing cardiac disease
- Extremes of age
- Pregnancy
- Low muscle mass
- Impaired hepatic function
- Reduced a1- glycoprotein levels

Question 7

Methods to reduce the risk of LAST

Answer 7

• Use the minimum effective dose
• Extra care in repeat dosing
• Consider adding adrenaline to reduce systemic uptake
• US guidance
• Aspiration before injection
• NR Fit
• Awake patients theoretically allows for earlier detection
• LAST box in areas where LA are given