Download Basics of ultrasound – 2 MGMC

Basics of ultrasound – 2
Dr. S. Parthasarathy
MD, DA, DNB, Dip Diab.MD ,DCA,
Dip software based statistics,
PhD (physiology) FICA
• Needling skills
Why we need such skills ??
• Regardless of experience, there is the ever
present risk of needle
misplacement with
damage to adjacent structures.
• arteries, veins, viscera nerve bundles, pleura.
• Occasionally,
such
damage
may
have
devastating implications for both the patient and
the practitioner.
• Fix the target with the transducer
• Get the needle towards the beam
• Move the needle more than the transducer
• Its not ideal to move the transducer to see the
needle
Don’t chase the needle
Needling skills
•
•
•
•
•
Transducer is positioned
We see the targets
Needle has to go in
It should reach the target
It should be seen in the screen
• Transducer
orientation
is
characterized
as
transverse and longitudinal in reference to the
physical
body
planes
(cross-sectional,
parasagittal),
• in relation to the ultrasound appearance of
anatomical structures (short-axis, long-axis).
In-Plane (IP) needle
•
•
•
•
•
the needle is followed in real time from penetration of skin
surface to deep anatomical target.
advantage of constant visualization during advancement of
the needle
minimize any aberrant needle direction and potential trauma
to nearby structures.
requires refined technical skills to keep the needle within the
sub-millimetre width of the ultrasound beam along its
trajectory.
This becomes increasingly difficult with the use of smaller
diameter needles and with deeper target structures.
In plane
Out of plane
• does not allow for continual visualization of the needle as
it passes through the tissues, but rather only as it passes
through the thin anatomical plane of the transducer
beam represented on-screen
• The Out-of-Plane technique conventionally does not
indicate the relationship of the needle to anatomic
structures either before or after it crosses the beam.
The white dot is which part of the needle ??
Two types of needle guidance
• Indirect
• Direct
• Do the USG
• fix the target
• Assess the depth and
structures
• Remove the USG
probe and insert the
needle
• Continuous
monitoring of the
needle path
• Real time
Needle guides
• direct the needle in a fixed, predetermined
direction to various depths
• from the transducer surface, depending on the
selected angle of the guide relative to the
transducer
• Especially indepth structures
• Disposable or reusable
Longitudinal or transverse
Approaches to venous
cannulation
• Longitudinal
•
long axis view – needle perpendicular
• Transverse
– Short axis view – needle parallel
• Hybrid
– Short axis view - needle perpendicular
Infection from transducers
• Cleaning the transducer between patients is essential.
•
Most
equipment
manufacturers
recommend
a
nonalcohol-based cleaning fluid.
• Over time, alcohol-based solutions will damage the seal
on the transducer scanning surface.
• the thin protective covering on the scanning surface of a
transducer can be damaged over time by use of abrasive
paper towels.
Pearls
• Large needles with guidewires inside
• Best visibility
• Smaller gauge needles- less artifacts
• More perpendicular needle better
visualized than acute angle
Scattering
• The needle tip may be visualized even
when the shaft cannot.
• The needle tip has a machined cutting
bevel with an irregular surface.
• Etching
• Polymer coating
Still not able to see
• short “in-and-out, side-to-side” motion
causes deflection of the adjacent soft
tissues
• Focus – if the needle is
• in the focused area ,
• it is better seen
Pearls
• Priming the needle with sterile water increases needle
shaft and tip brightness
• When the needle shaft crosses the ultrasound beam,
an acoustic shadow forms, which may be used to
indirectly assess needle position.
Pearls
• to achieve close alignment of the US
beam and needle - recognise that very
small movements of either the needle
or the probe are required.
• Don’t move both
Pearls
• the injection of fluid may improve needle
and catheter tip visualization.
• Rotating the stylet inside the needle may
improve visualisation
• If we have no further problems – inject air !!
Pearls
• When the needle tip is close to the nerve and small
amount of LA can be injected.
• The LA will usually create an open space around part
of the nerve.
• This potential space -- safely advance the needle.
• the 'Doughnut sign,' where a dark ring of LA
completely surrounds the nerve
Dot does not mean position
Dot does not mean position
Tofu model
• Mashed soya beans
• Wood
• Rubber tubings
Needling with GPS
Target reached red--- needle reached green
• The needle sets up an electromagnetic
field which is picked up by a transducer
• It is usually better visualised upto a depth
of 4 cm.
SAFETY
• Does not involve any of the problems associated with
ionizing radiation, which limits the use of modalities
such as X ray, computed tomography (CT), positron
emission tomography (PET).
• MRI – working close to a strong magnetic field ??
• But USG – impeccable safety record !!
Mechanisms of damage
• Cavitation
• Microstreaming
• Heating
Cavitation
• small gas collections, normally pre-existing, in either
the bloodstream or possibly interstitial spaces in tissue.
• the US wave consists of alternating positive and
negative pressure phases.
• the bubbles will alternately be compressed and
stretched.
• Compression and rarefaction
• Bubble grows – implode – inertial cavitation
• Bubble shrinks – Non inertial cavitation
What is the
biological change
due to this ??
Possibly some benign
biological change
Microstreaming
• passage of an ultrasound wave through a liquid
can cause a flow or stirring action, called
microstreaming.
• Possible alteration in the permeability of the
membranes of nearby cells.
Heating
• World Federation for Ultrasound in
Medicine and Biology (WFUMB)
• A diagnostic exposure that produces a maximum in
situ temperature rise of no more than 1.5 *C above
normal physiological levels (37*C) may be used
clinically without reservation on thermal grounds
• How to know that ??
Heating
• National Electrical Manufacturers Association (NEMA)
• Onscreen labelling
• Mechanical index
• Thermal index
• If MI is less than 0.3 – cavitation is less – OK
• TI is less than 1 – heating is less – OK
• More protein
• More time
• More beam width
• More heat
Think of TEE – time
prolonged
Chemical
• Depolymerisationcan
breakdown
experimentally
ultrasound
polysaccharides
and
polypeptides including DNA.
• These effects have not been reported to occur in
vivo
following
diagnostic
ultrasound
procedures.
• Normal is 10 mW/cm2--100 mW/cm2 is dangerous
• High intensity, high frequency ultrasound has
been shown to result in adverse effects including
:Tissue necrosis
• Chromosomal damage
US as analgesic ?
• Genetic mutations
• Teratogenic changes
Summary
• In and out of plane
• Direct and indirect USG guidance
• Three approaches of needle in vein
• Pearls of needle vision
• Safety cavitation, microstreaming and heating,
chemical
• Thank you all