16. Local Anaesthetic toxicity Flashcards
Intro
Over the last decade there have
been significant improvements in the
delivery of regional anaesthesia including
ultrasound-guided nerve blockade,
which allows accurate delivery of local anaesthetics
and the introduction of less cardiotoxic local anaesthetics such as levobupivacaine and ropivacaine.
Nevertheless, local anaesthetic (LA)
toxicity remains an ever-present
risk and as such, the emergency management is a core topic.
The Association of Anaesthetists of Great Britain and Ireland (AAGBI) has produced guidelines for the management of severe local anaesthetic toxicity,
and examiners will expect a clear and concise reproduction of these guidelines in an exam
situation.
Factors to consider in the development of LA toxicity
Include the
LA itself,
site of injection,
speed of absorption and
the consequent rate of rise in plasma concentration.
The physiological and metabolical state of the patient may also play a role,
e.g. hypoxia,
hypercarbia and
acidosis all potentiate cardiotoxicity.
For all these reasons,
the actual maximum recommended dose of LA needs to be interpreted in the correct clinical context.
However, examiners would expect you to know the recommended maximum doses:
LA
Max dose
Lignocaine
Bupiv + Levo
Ropiv
Cocaine
Amethocaine
Prilocaine
Lignocaine 3 mg/kg 7 mg/kg (adrenaline)
Bupivacaine 2 mg/kg –
Levobupivacaine 2 mg/kg –
Ropivacaine 3 mg/kg –
Cocaine 3 mg/kg –
Amethocaine 1.5 mg/kg –
Prilocaine 6 mg/kg 8 mg/kg (felypressin)
What are the clinical features of LA toxicity?
Clinical features
depend on plasma concentration of LA.
For example,
early symptoms in an awake patient
with a plasma lignocaine concentration
of 2–4 μg/mL may include
light-headedness,
tinnitus,
circumoral tingling
and tongue numbness.
Plasma levels between 5 and 10 μg/mL will lead
to visual disturbances,
agitation and muscular twitching.
Plasma levels above 10 μg/mL may lead to
tonic–clonic convulsions followed
by coma and respiratory arrest.
At plasma levels of 15 and 25 μg/mL
cardiotoxicity will result,
leading to cardiovascular collapse
and development of malignant arrhythmias
(conduction blocks,
ventricular tachyarrhythmias and asystole).
Describe your management of LA toxicity.
State that this is an anaesthetic emergency
and that you would call for senior
anaesthetic assistance and
make a rapid but thorough assessment of the
patient.
> Stop injecting the LA.
> Maintain and, if necessary,
secure the airway with a cuffed endotracheal
tube.
> Administer 100% oxygen
and ensure adequate lung ventilation
(hyperventilation may be of benefit by increasing pH).
> Confirm or establish IV access.
> Control seizures using a benzodiazepine (e.g. lorazepam) or
use small incremental doses of thiopentone or propofol.
> Assess cardiovascular status throughout. Arterial line insertion would be of benefit.
Management of cardiac arrest > Commence cardiopulmonary resuscitation (CPR) following Advanced Life
Support (ALS) protocols.
> Manage arrhythmias using the same ALS protocols, recognising that arrhythmias may be refractory to treatment and prolonged resuscitation
(several hours) may be necessary.
> It may be appropriate to consider other treatment options:
- Consider cardiopulmonary bypass if available.
- Consider treatment with lipid emulsion.
Treatment of cardiac arrest with lipid emulsion
Approximate doses for a 70 kg
patient are given in italics:
> Administer an intravenous bolus of Intralipid® 20% (1.5 mL/kg) over 1 min (100 mL bolus).
> Continue CPR.
Start an infusion of Intralipid® 20% at 0.25 mL/kg/min (400 mL over 20 min).
> Repeat the bolus injection (100 mL) of Intralipid® 20% twice at 5 min intervals
if an adequate circulation has not been restored.
> After another 5 min, increase the rate of infusion to 0.5 mL/kg/min if an adequate circulation has not been restored (400 mL over 10 min).
> Continue infusion until a stable and adequate circulation has been restored.
Remember
> Continue CPR throughout treatment with lipid emulsion.
> Recovery from LA-induced cardiac arrest may take >1 hour.
> Propofol is not a suitable substitute for Intralipid® 20%.
> Replace your supply of Intralipid® 20% after use.
Follow-up action >
Inform the patient of the event, answer any questions and ensure medical
documentation is complete.
> Complete a local hospital critical incident form.
> Report case to the National Patient Safety Agency (NPSA) (via www.
npsa.nhs.uk).
