46. IVRA + LA toxicity

Question 1

You are anaesthetising for a list that includes a 60-year-old man for
superficial forearm surgery to be done under intravenous regional
anaesthesia (Biers block

How would you proceed?

Answer 1

Check with the patient and the surgeon the exact nature
of the surgery as intravenous regional anaesthesia (IVRA) is mainly suitable
for skin surface surgery and the effect reliably lasts for about 30 minutes.

The patient should be assessed and prepared as for any other anaesthetic
(although there is no evidence to suggest that the patient comes to any
harm by not being fasted as the incidence of complications is so rare).

Suitable IV access (usually 20G) is obtained both in the operative arm distal
to the cuff and in the non-operative arm.

Establish routine monitoring.

A double-cuffed tourniquet is applied to the upper arm of the operative
limb.

An Eschmarch bandage or elevation is used to exsanguinate the limb.

The distal then the proximal cuffs are inflated to 100mmHg above the
systolic BP.

Inject a dilute solution of local anaesthetic and wait 10–15 minutes for the
block to take effect.

Question 2

What local anaesthetic would you use?

Answer 2

Usually prilocaine 0.5%, 40–60 ml depending on the size of the arm (max
dose 6 mg/kg).
Prilocaine is an amide local anaesthetic, which has less protein binding than
others and has the advantage that it is more rapidly metabolized (hepatic
and extra-hepatic) and hence less toxic.

Prilocaine is closely related to lidocaine and is very similar in its clinical
action. It can cause methaemoglobinaemia when used in high dosage

(>600 mg) – this is usually benign and resolves within a couple of hours. The
treatment is methylene blue 1 mg/kg i.v. over 5 minutes.
Lidocaine 0.5% up to a maximum dose of 3 mg/kg is an alternative.

Question 3

What would you do if the patient complains of cuff pain?

Answer 3

It is possible to deflate the distal cuff for a few minutes leaving the upper
proximal cuff inflated, and then inflate the distal cuff again over the now
anaesthetised skin.

The upper proximal cuff can then be deflated.

This does remove the safety feature of the double cuff.

As some of the anaesthetic effects and discomfort are probably caused by
ischaemic neuropraxia, this may not solve the problem of cuff discomfort.

Question 4

What precautions do you take to avoid systemic toxicity?

Answer 4

The double cuff remains inflated for a minimum of 15 minutes for
prilocaine or 20 minutes with lidocaine (which takes longer to metabolise
and ‘fix’ to the tissues).

There are strict maximum doses which should not be exceeded. Secure i.v.
access and monitoring is mandatory prior to the injection of large doses of
local anaesthetic. Full resuscitation equipment must be immediately
available.

Question 5

If the cuff leaks, what symptoms and signs would you expect to see?

Answer 5

Systemic toxic effects due to local anaesthetic overdose primarily involve the
central nervous and cardiovascular systems.
In general, the CNS is more sensitive to local anaesthetics than the CVS, so
CNS manifestations tend to occur earlier.
Brain excitatory effects occur before the depressant effects.
Usually about 4–7 times the convulsant dose needs to be injected before
cardiovascular collapse occurs.
Bupivacaine is more cardiotoxic than lidocaine, which is why it is not used
for IVRA.

Question 6

CNS symptoms and signs include the following:

Answer 6

Perioral + tongue paraesthesia

Metallic taste

Dizziness

Slurred speech

Diplopia

Tinnitus

Confusion

Restlessness

Muscle twitching

Convulsions/coma

Question 7

CVS symptoms

Answer 7

result from progressive sodium channel blockade with the
eventual formation of re-enterant tachycardias:

Bradycardia

Prolonged PR interval

Widened QRS

Progressive conduction blockade

Re-enterant tachycardias

VF

Question 8

Do you know of a specific antidote to LA toxicity?

Answer 8

Intralipid R has been used successfully to restore electrical activity after the
failure of conventional resuscitation in cardiac arrests. It has been reported in
case reports as a successful therapy during prolonged cardiac arrest following
local anaesthetic blocks and toxicity.

Immediately
* Give an initial i.v. bolus of lipid emulsion 1.5 ml.kg–1 over 1 min
(~100 ml for a 70 kg adult)
* Start an i.v. infusion of lipid emulsion at 15 ml.kg–1.h–1
(17.5 ml.min-1 for a 70 kg adult)

At 5 and 10 minutes:
* Give a repeat bolus (same dose) if:
o cardiovascular stability has not been restored or
o an adequate circulation deteriorates
At any time after 5 minutes:
* Double the rate to 30 ml.kg–1.h–1 if:
o cardiovascular stability has not been restored or
o an adequate circulation deteriorates

In 2007, The AAGBI published guidelines for the
management of severe local anaesthetic toxicity. These include the possible
use of cardiopulmonary bypass and lipid emulsion