Even this paper is very speculative Ray; fitting eight minutes after cuff
deflation doesn't sound like local toxicity to me. There was a long
tourniquet time so acidosis is also possible although again, the long
interval from cuff deflation makes this less likely. I think the authors
were just hoping it was a prilocaine fit so they could report it as a rare
complication!

Adrian

----- Original Message -----
From: "Ray McGlone" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, September 30, 2002 9:04 PM
Subject: Re: Bier's Block


> 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
> >