The current trend for performing nerve blocks in regional anaesthesia is to use
ultrasound guidance These machines are however expensive and
beyond the reach of a large part of the anesthesia population. Currently about
80% of all regional anesthesia is still performed using a nerve stimulator. Also
ultrasound guidance requires a learned skill with a definitive learning curve
and requires proper training and education. That is a worldwide movement to
using ultrasound guidance. Ultrasound blocks more and more
because it has certain advantages of locating the nerves exactly where they
are. It helps you to identify aberrant nerve placements where they are not usually expected
to be and also you can actually visualise the needle approaching the nerve so it
should theoretically eliminate nerve injuries. So worldwide the use is to
using ultrasound but these machines are very expensive and which puts them out
of reach of a large section of the anaesthesia population that just
simply cannot afford these machines. Unfortunately because all the attention
has been focused on ultrasound machines, the technology of nerve stimulators has
lagged behind and this is where the Xavant nerve stimulator is very unique
and that it's a very high-tech machine with a lot of high-tech features but it
has the most important feature is the mapping probe and you can map
the nerve and I'd locate the nerve percutaneously before you make a needle
puncture. This brings it very close to achieving what an ultrasound machine
does and that is locating the nerve to prevent somebody who's not quite sure of the
anatomy puncturing the skin and poking around looking for the nerve and also
even in the hands of an experienced nerve blocker the nerve might not be
where it should be. There are anatomical variations
however the mapping probe allows you to identify the nerve percutaneously and
you can do your nerve puncture accurately. This saves both time and
makes the block more accurate at the same time. The Stimpod consists of the
stimulator pulse generator, a nerve mapping probe, a lead that connects to
the stimulating needle, the positive return lead. Here we have the machine in
the mapping mode. Here we have the pulse width. In order to get the best
stimulation through the skin one needs to have that on 0.3 milliseconds
and by pressing that button it changes to 0.3 milliseconds and as one has
the probe in place one will raise the current until you get the twitch in the
arm in the correct place. Now it is on 0.3 so we will proceed to do our
block. At the start of the procedure landmarks are marked on the skin to give
an approximate idea of where the nerve is to be expected. There we have the
patient's neck area that has been draped and prepared for doing the interscalene
block. There we have the posterior border of the sternomastoid muscle. This
line marks the level of the cricoid cartilage which gives us an idea where C5
C6 level in the neck is. Here's the external jugular vein and here is the
interscalene groove which we have palpated digitally. There's our finger in
the interscalene groove. That's where we expect to get our brachial plexus. When
using the Stimpod one can locate the nerve through the skin by placing the mapping
probe where one would expect the nerve to be and when one stimulates the nerve
through the skin one can look through the skin percutaneously to find the ideal twitch. In
this case we're looking for the forearm flexes as we see there. Now I know
exactly where my nerve is under the skin
When one gets the twitch one must also try and look to find the area of maximum
twitch because the probe's point is round and can be stimulated in the nerve a bit
from the side. Your greatest current density is in front of the needle so
we'll try and get the front of the needle over the nerve to get the best
twitch. The mapping probe is held in position to identify the nerve and the
needle is approached right up to the point of the mapping probe. As soon as
the needle touches the skin the machine automatically switches from stimulating
on the mapping probe to simulating on the needle. One has to then change the
current to 1.2 milliamps and the needle is advanced through the skin and
the twitches are obtained like that. One can now take away the mapping probe and
identify the twitch, and there we have it.
We reduce our current
down, and we're still getting this slight twitch
When the block is performed this way between 5 and 10 ml of
local anesthetic is usually sufficient because it is very very accurately placed.
One can see that the needle's tip is exactly in the interscalene groove. Remove the
needle and that will be a successful block. What are the advantages of using
the Stimpod nerve locating technique compared to other nerve stimulators. The
thing is that when you locate the nerve percutaneously with the
mapping probe you can hold it there in position and you bring your needle up to
the tip of the probe and as soon as the needle touches the skin the machine
automatically changes from stimulating on the probe to stimulating on the needle
With other nerve mappings you will map the nerve and maybe mark the skin
where the nerve is and then go to the needle and try to locate the nerve where
the mapper said it was. With the Xavant machine you hold the nerve
in position with a bit of pressure from the probe and you put your needle
exactly there and that's where you find the nerve. So the
big feature is that it changes automatically from the one to the other
on contact with the skin