hi everyone this is Lahiru from abc's of anesthesia and in this
video we're gonna go through a really niche topic that not many people would
really think about that often but it's how to optimize your flashback in your cannula
so i want to thank brenton edwards for this comment which really requested this so
i'll put it at the top of my priority list and here we go i'm going to start making this video
so the first question is why would you want to even put saline in your cannula chamber
so right now here we have the chamber of the cannula right there and we're going to fill
that with saline and that's going to speed up the process of flashback and i'll tell you why
that's really important so the way we do that is essentially take that little cap off and then
put some of this solution into there and i'll show you that as we get into a bit more detail
so the first thing i want to tell you is flashback is absolutely vital it's the only indication that
you have without other fancy techniques like ultrasound it's the only indication that your
needle and cannula is actually in the vein so what i mean by that is you've got your needle and let's
imagine that this syringe is a vein let's say you go through the skin and then you know you're
not getting any blood in this chamber until you actually enter into the vein itself so once you're
in the vein then you know that your needle's in the vein and that's why you have to lower the
angle and then advance it down before pushing off the cannula so flashback is vital it's the first
indication the only indication that your needle is actually inside the vein so the only reason
we get flashback is besides the needle being in the vein the venous pressure is higher than
atmospheric pressure so there's a push of liquid from the high pressure area to the low pressure
area which is in that chamber so for example if i was to just get a normal 22 gauge cannula like so
it's what i've done to demonstrate this i've got a bag of csl combined sodium lactate i've just put
some red food coloring in it so it's not blood and what i'm going to do is pretend that that's
a vein so i'm going to access it through this port here so that i don't have to access an actual vein
and then we'll see what happens now first of all the pressure in this bag is actually not very
high there's not much you know there's a lot of laxity in that so if i was to
use this 22 gauge needle and just put it through this artificial vein you'll see that there's
actually no flashback occurring and it's only through the increase of pressure so let's say
this is going to be an increase in pressure now you get that flashback occurring
so you need some kind of venous pressure for flashback to even occur so that's the first thing
now usually flashback is instant so everything we're talking about about putting saline
in the chamber doesn't usually matter because there's a vein with high enough venous pressure
and you've got a needle that's got a large enough metal tube and chamber there so even at 22 gauge
in a high pressure vein it's not a problem at all but if the vein is a very low pressure vein
or very small spindly vein fragile vein that's when you're gonna have problems and that's when
your flashback is gonna be incredibly incredibly slow so the main situation is that you have very
very low pressure veins are just the small veins so these are neonates pediatric veins
and as well as those really tiny veins you might see in elderly patients but even even
on on your wrist for example if you take any small vein unlike your feet or your wrist these
small veins anywhere are very low pressure and the flashback will take a lot of time to occur
so now in this scenario of having a very small needle it has a very small needle and chamber
in a very low pressure small vein the problem is that your flashback is not going to be quick
enough so imagine that scenario let's imagine that this is actually a 24 or 22 gauge needle
and this is a very very tiny vein imagine that you go into the vein but because it's so small
and there's so low pressure the flashback doesn't traverse up this fast enough and you
just keep going through so you go through the other side and then you might see the flashback
that means that you're already through the other side now there's obviously a solution to this
you just need to go really really slowly in the smallest most fragile veins using the smallest
cannulas if you go really quickly you don't get flashback and you have a problem your veins your
needle's already on the other side of the vein but if you go really really slowly take your time
then you get flashback and then you know that's time to flatten out and advance
now besides going slowly method that's been passed down from my supervisor and my seniors to myself
and the thing i passed down to my juniors is to put saline in that chamber of the cannula and that
will speed up flashback the reason for this is now instead of having fluid in the vein so blood
and air in your chamber so now you need an actual pressure differential what happens is when you
put liquid like saline it means that you get a flashback not just through a pressure gradient
but also through diffusion and i'll show you what i mean with this demonstration in this
first scenario i've got a 22 gauge needle and i've got no sailing in the chamber it's just there it's
just as it comes normally now what i'm going to do i'm going to imitate puncturing through the vein
and let's just see how quickly it happens so puncturing the vein now it's through there now
and then you'll see that the flashback has occurred in the chamber right there
so that's the first scenario so in the second one i take my cannula
i uncap it as normal i then take off this little device here so that just comes off like that
make sure that's all clean and sterile obviously i'm not doing aseptic non-touch
technique for this demonstration i take a syringe of saline and i simply
put saline into that chamber until it drips out the other side as you can see so now that whole
needle column is filled with saline i remove my syringe and then i recap it in a clean fashion
so now i've got a cannula nothing's changed except the fact that i've now got
saline a saline fluid column throughout the whole needle and into the chamber
so as i enter the vein you'll see a different quality to the flashback
as you can see it kind of squirts out the other side
so that's the reason why you sound in the chamber in the smallest most difficult veins
especially pediatrics neonates and just adults with really difficult veins so i go slowly
really really slowly waiting for that flashback to occur but i also use saline in the chamber to
get a quicker flashback to make sure that i don't go through the other side so that's the reason i
use saline in the most difficult veins so if you enjoy this video that's a really simple technique
that i use for the most difficult cannulas um please write any comments any feedback or any
other techniques that you might have for the most difficult cannulas so please write in the
comments below and uh yeah i'll see you next time for the next video thanks a lot bye-bye