Adrian,
I like you have never had a problem with prilocaine over the years. I can
only find one case report of fitting once the cuff was released (see below).
This must be 1 case in hundreds of thousands in the world over the years.
Source
Anaesthesia. 49(7):642-3, 1994 Jul.
Generalised Convulsions after intravenous regional anaesthesia with
prilocaine
We wish to report an unusual complication associated with the use of
prilocaine. A healthy 47-year-old man (55 kg, 162 em) was scheduled for
removal of two screws in his right ankle under intravenous regional
anaesthesia (IVRA). He was premedicated with pethidine 40 mg and
promethazine 20 mg intramuscularly 60 min before starting IVRA. After
exsanguination of the right leg, IVRA was performed with prilocaine 4
mg.kg-' injected over 2 min. The cuff was deflated 50 min after start of
IVRA blood pressure and heart rate were stable and Spo, 98%. Eight min after
deflation of the cuff generalised convulsions occurred. Ventilation was
immediately controlled via a face mask with an Fio. of 1.0 and thiopentone
given. The convulsions stopped completely. but some ventricular
extrasystoles and bigeminy were noticed for 2-3 min. The patient recovered
completely 17 min after the appearance of the convulsions. Unfortunately,
blood samples for plasma concentrations of prilocaine were not collected.
Electrolytes and blood glucose measured after the event were normal. An EEG
was performed which showed no epileptic focus, but a posttraumatic
irritative zone with very little activity in an area close to a suspected
old temporal fracture. CT scan did not show any abnormality and his
neurological status was normal. The patient confirmed a head injury in his
childhood followed by occasional episodes of dizziness, but denied any
convulsions. He left the hospital on the second postoperative day; no
medication was required and he had no complaints.
Although plasma prilocaine levels were not measured, we still consider that
the principal cause of the convulsions was the release of prilocaine into
the blood stream at the time of the tourniquet's deflation. The convulsions
appeared at a time after cuff deflation when plasma levels of prilocaine are
the highest [1, 2].
Promethazine can bind to H2 recaptors in the CNS and stimulate or depress
it. Pethidine. is predominantly a u-agonist and it exerts its chief
pharmacological actions on the CNS and in toxic doses sometimes causes CNS
excitation, characterised by tremors, muscle twitches and seizures. These
symptoms are usually due to an accumulation of its metabolite norpethidine.
An association with promethazine can slow the metabolism of pethidine, and
reinforce the sedation effect. Although the patient had been fasting for 12
h, hypoglycaemia is an unlikely cause of convulsions. We think therefore it
is reasonable to consider that the convulsions were due to prilocaine even
if this drug is considered as one of the safest local anaesthetics for 1VRA
[3, 41.
Given its efficacy by the intravenous route and the low
incidence of thrombophIebitis, prilocaine appears to be the most suitable of
the drugs available for 1VRA [51. Comparison of prilocaine and lignocaine
after intravenous injection showed that the plasma concentration of
prilocaine was far lower than for lignocaine and that a large quantity of
prilocaine is extracted by the lungs on the first pass [61. Similar results
are reported when plasma levels of prilocaine and lignocaine are compared
after release of the cuff during IVRA [71. Lack of correlation between
plasma concentration of local anaesthetics and presence or severity of
symptoms was demonstrated in several studies[ 1, 81. In one of these,
although a dose of prilocaine of only 3 mg.kg-' was used, mild CNS symptoms
(dizziness, lightheadedness and auditory disturbances) were observed after
cuff deflation, 20 min after injection [81. In our case, an EEG a few hours
after the event showed a small irritative inactive zone in the temporal
area, but no epileptic focus. We have been unable to find any evidence to
support the hypothesis that a previous head injury will lower the threshold
for convulsions due to local anaesthetics. To our knowledge, this is the
first case report of' generalised convulsions after an otherwise uneventful
IVRA with prilocaine 4 mg.kg-'. We presented this case to make clinicians
aware of the fact that generalised seizures can appear even after an
uneventful IVRA with this dose of prilocaine and that recommendations for
monitoring. and availability of resuscitation equipment must be adhered to
even when using prilocaine in 'safe' dosages for 1VRA.
University ' r Hospital of Basel, C. KERN
Basel, Switzerland
Universit ' r Hospital of'Genei,a, Z. GAMULIN
Geneva, Switzerland
----- Original Message -----
From: "Adrian Fogarty" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, September 30, 2002 7:00 PM
Subject: Re: Bier's Block
> ----- Original Message -----
> From: "Stephen Hughes"
> > As for bier's blocks, I have never seen one because of the mythology
> surrounding them and the lack of prilocaine. Would you believe that?
>
> You could always do a few weeks here in Hampstead, Stephen, and we'll show
> you a few Bier's blocks. You'll have to drop the 'Arlow accent however
> (sorry, I know you've been perfecting it over the last four years).
>
> Steve Meek wrote:
> > Now at Frenchay using prilocaine 1% diluted down to 40mls (0.5% without
> problems)
>
> Yes, I dilute 20mls of 1% with 20mls of water to produce 40mls of 0.5%. I
> presume saline could be used instead.
>
> > I am sure prilocaine is safer than lignocaine and agree with Ray that it
> is then a safe SHO procedure: staring patients, 2 doctors being present
etc
> is unnecessary
>
> I agree but haven't quite delegated this to SHOs yet. However all of ours
> are first years who are now less experienced than ever! I personally don't
> starve or monitor these patients, and I don't use second lines or second
> doctors either. Am not convinced I need to as I haven't seen any problems
> after 12 years' use. Does anyone know, is there any risk of significant
> morbidity using prilocaine? And I've never needed supplemental analgesia
> Ray!
>
> Adrian Fogarty
>
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