of the drug. It's a one shot technique.
So this is what happens with a spinal.
The needles we use for spinals now are very small
needles, and I'll show a picture in a moment
of what the tip of the needle looks like, because has been
a dramatic change in the shape of these needles over the years.
But the needles are small, they're very, they're very
fine needles. They actually have to be
put through an Introducer. So the first thing we do is, we put
some local anesthetic in the patient's skin. We place
an introducer in the position that we want to pass
the spinal needle, and then we pass the spinal
needle through the introducer. And, as you become more
experienced, you can feel the needle popping through
various levels of ligaments. You hit
the Ligamentum flavum and you get
quite a big pop. And then you advance just a tiny bit more,
that 2 or 3 millimeters that I mentioned before,
and you can feel another pop. And
at that point, if you take the stylet
out of the needle, you get cerebral spinal fluid
coming out as you can see in this picture.
As soon as that happens, you disconnect the syringe,
you take a syringe that's already been pre-loaded with
a local anesthetic, you attach it to the spinal needle,
and you inject it. And within seconds, the patient
will note that the bottom and the legs are
warming up. And within a very few minutes
the legs and the middle part of the body just
simply disappears. So these are two types
of spinal needles. The one in the middle is called
a Quincke needle. And this is an old
fashioned needle, although we still use it in some situations.
They tended to be larger needles, but you can see that
the tip of the needle is sharp, and you may not be able
to tell from the picture, but that whole area around
the hole in the needle tip is a cutting edge,
and it will cut through tissues very easily.
The problem with this needle is that, it caused
holes that were big enough for cerebral spinal
fluid to continue to leak out of the central
nervous system, after the block
was in place. And this could lead to extremely severe
headaches, which were sometimes quite difficult
to treat. About 20 years ago a new type of needle
was introduced, and this was the Sprotte
needle. And that's the one on the right of this diagram.
And you can see that the tip is different, it's a pencil point
tip. It has no cutting edge. It basically
forces its way between the fibers of
the ligaments without cutting them. The hole
in this needle is not right at the tip, it's down,
a little bit down the shaft. And in the Sprotte needle it was
a very big hole. And that became a problem because
it was possible to have a portion of the hole
in the sub-arachnoid space, and a portion of it outside
the sub-arachnoid space. So that when you injected the local
anesthetic, some of it would go into the right place, but some of it
would just get lost. The needles we use now are,
the ones that I use now, are called Whitacre needles,
and they're very similar to the Sprotte, except the hole
is much smaller and much closer to the tip.
And the chances of injecting local anesthetic
into the wrong space is largely eliminated.
The incidence of headaches with these
needles is well under 1%, whereas
with the Quincke needle in pregnant women
it was around 60%. So it's a huge change and
it's allowed us to use spinal analgesia in obstetrics,
whereas before we had to use epidurals.