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Ultrasound guidance for the placement of central venous catheters is quickly
becoming the standard of care
before ultrasound was widely available most central venous catheters were placed
using blind techniques that relied on anatomic landmarks
to estimate the location of vessels.
blind techniques may result in complications in as many as twenty
percent of cases
there is strong evidence that central venous catheter placement with real time
ultrasound guidance is safer than blind techniques
in 2001, an evidence-based report entitled
"Making health care safer"
prepared for the United States Department of Health and Human Services
strongly recommended using real time ultrasound guidance for the placement of
central venous catheters.
vascular ultrasound allows immediate identification
of anatomic variations and confirmation vessel patency
realtime ultrasound guidance of line placement allows direct visualization of
a needle entering the vessel
It has been proven to decrease the incidence of complications
and to decrease the time required for successful line placement
static ultrasound guidance in which ultrasound is used only to determine
insertion site but not for direct visualization during a procedure is less
successful than real time ultrasound guidance
the identification of vascular structures is relatively straightforward
the difference between veins in arteries can be determined by compressibility and
shape
patent veins are completely compressible
have thinner walls and an ovoid shape
arteries are difficult to compress have thicker walls and are circular in shape
veins may collapse completely
and may be difficult to identify if the patient is upright or semi-upright
placing the target main in a dependent position and having the patient perform
a valsalva maneuver may dramatically increase the size of central veins
and makes identification and cannulation much easier
a high frequencies linear or micro convex probe is usually best for line
placement
the frequency of vascular probes is usually 6-14 megahertz
the ideal probe for lines placement will vary depending on which vessel is to be
cannulated
the depth of the vessel
the size of the patient
and the orientation of the probe in relation to the vessel in either the transverse
or longitudinal plane.
a sterile glove can be used as a probe covered during central line placement
but it is best to use a commercially available sterile probe cover
sterile probe cover kits contain a long plastic sleeves, sterile gel and small
rubber bands to secure the sleeve
to apply the sterile probe cover, have an assistant place
non sterile gel inside the sleeve
and then place the probe into the sleeve
point your sleeve over the probe in court
place the rubber bands to hold the cover in place
play some sterile gel
on the tip of the probe once a sterile cover is in place
one of the most important aspects of ultrasound guidance line placement is the
orientation of the probe in relation to the target vessel
realtime guidance can be accomplished by imaging the pain in either the
transverse or luongitudinal plane.
the transverse approach allows for identification of the vein in relation to the
associated artery
the transverse approach is technically easier than longitudinal approach. And it's the
best method for beginners
with the transverse approach the needle passes diagonally through the ultrasound
plane
and appears as a single break echogenic four signs on the ultrasound image
the needle is very echogenic and produces a ring down artifact and shadowing
beginners may mistake the ring down artifact and shadowing for part of the
needle
it is important to realize
that the needle tip is not usually visualized in the transverse plane
this can lead to errors in depth perception of the needle tip and injury to
structures deep to the veins.
the best way to determine the location of the needle is to look for movement of
the soft tissue adjacent to the needles.
subtle back-and-forth movements such as bouncing or wiggling of the needle during
insertion
causes movement of the surrounding soft tissue
which is easy to appreciate on the ultrasound image
since the exact location of the needle tip is not obvious, it is important to note
the depth of the vessel on the ultrasound image
and be careful not to insert a needle beyond the depth of the vessel
It may be possible to see tenting of the anterior wall or complete collapse of
the vein
when the tip of the needle
presses against it
a quick forward movement of the needle at this point may help to puncture the
vessel wall
the return of blood confirms intravascular placement the needle tip
the main benefit of the transverse approach is that it allows simultaneous
visualization of both the artery and vein
this allows the operator to advance the needle toward the vein with almost no
danger of hitting the artery
the longitudinal approached gives the sonographers much more information during the
line placement procedure
however the longitudinal approach is more difficult and can be frustrating
for inexperienced sonographers.
when the longitudinal approach is mastered
it can be used to directly observe the needle and the needle tip
as it is advanced into the vessel
when the needle tip is clearly inside the vein in the long axis view
it is not necessary to drop blood back
and the guidewire
can be advanced and directly observed as it is advanced into the vessel
dynamic ultrasound guidance can be accomplished with a one or two persons
technique
a two persons technique with one holding the ultrasound probe and one performing the line
placement procedure
can be easily employed if the transverse approach is used
when the longitudinal approach is used the plane of the ultrasound and the plane of
the needle
must be perfectly aligned
so it is best for one operator to hold both the probe and the needle
there are several locations in which central vein can be cannulated with
dynamic ultrasound guidance
the internal jugular vein is often the best choice for ultrasound guidance central
line placement
the internal jugular vein can be cannulated in the usual position
between the heads of the sternocleidomastoid muscle
and may also be cannulated in any other location where there is minimal soft
tissue between the skin and the vessel
pulled the probe with the [__] to the patients left side
so that the patient's lestside is on the left side of the monitor
the patient's right side
is on the right side of the monitor
the crowded artery will usually be the more medial structure and internal
jugular vein will be more lateral
However, there is significant variability in the position of the internal jugular vein in
relation to the carotid artery
and it may be found
overlying or even medial to the artery
the vein can be identified by compression venus flow with doppler
or increasing size with valsalva maneuver
placing the patient in the trendelenburg position
or having them perform a valsalva maneuver
may significantly increased the size of the internal jugular vein
the position of the patients neck can also influence the relationship of the
vein and the artery
turning the head may cause the artery and vein to overlap rather than be side by
side
holding the probe in a more anterior position
parallel to the floor
rather than laterally
will also help to align the vessels any side by side position
for the transverse approach, once the target vessel is identified it should be
centered underneath the probe
the ultrasound probe should be held in your non dominant hand
insert the needle and slowly advanced the needle while watching the ultrasound
screen
the needle will appear as a
hypoechoic or bright dot with a ring down artifact
buckling of the vein will appear on the screen
when the needle tip is at the wall of the vessel
at this point
use a gentle jabbing motion to cannulate the vein
once the needle cannulate the vein under ultrasound guidance you can then drop
the probe on your sterile field and proceed with line placement in the
usual fashion
for the longitudinal approach be sure to differentiate the vein from artery by
locating both vessels in the transverse orientation
then turn the probe ninety degrees to visualize just a vein in the long axis
the marker dot
should align so that the left side of the monitor is sufflate
enter the skin just adjacent to the end of the probe in advance at about a
forty five degree angle
when the needle is about one centimeter deep look for the needle tip on the
monitor
then advance the tip of the needle into the vein under direct visualization
when the needle tip is in the vein advance the wire and watch it pass into
the vein
the femural vein is also a good location for ultrasound guide central
line placement
the femural vein is identified by placing the probe just below the inguinal ligament
with the marker dot toward the patient's right
so that the patient's right side
is on the left side of the monitor and the patient's left side
is on the right side of the monitor
conventional teaching is that the femural vein is mediall to the artery
however in more than fifty percent of patients, the vein and artery are
overlapping
if the artery completely overlaps the vein is best to go to the contra lateral
side
or slide the probe distally to find a point where the artery in vein are side
by side
the vein is identified using compression and either the transfers or longitudinal
approach can be used
the traditional approach to the subclavian vein is difficult using
ultrasound guidance because the proximal portion of the vessel is directly
beneath the clanical
howeverthe subclavian vein can be cannulated more distally using
ultrasound guidance with a longitudinal approach
a subclavian vein in our artery is first identified
at about the midpoint of the clanical
with the probe in a transverse plane
and the marker dot aimed toward the patient's head
once the vein is identified the probe is turned ninety degrees with the marker
dot toward the patient's right side
the needle is then advanced under direct visualization
to ensure that the needle tip is not inadvertently advanced too deeply
the plural interface can be seen just deep to the subclavian vessels
using ultrasound for line placement is relatively straightforward and easy to
learn the most difficult aspect of the procedure is learning how to identify
veins and arteries in relation to one another and how to follow the needle tip
toward the target vessel