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8/13/2019 Reality n Myth - Anaesthetists and Ultrasound
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Reality and myths
Anaesthesiologist and Ultrasonography
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THE ROLE OF AN ANAESTHETIST
Anaesthetists form the largest singlehospital medical specialty and their skills
are used in all aspects of patient care.
Whilst the perioperative anaesthetic care
of the surgical patient is the core of
specialty work (and this includes all types
of surgery from simple body surface
surgery in adults to the most complex
surgery in patients of all ages, including
the premature newborn) manyanaesthetists have a much wider scope of
practice which may include:
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The preoperative preparation of surgical patients
The resuscitation and stabilisation of patients in the Emergency Department
Pain relief in labour and obstetric anaesthesia Intensive care medicine
Transport of acutely ill and injured patients
Pre-hospital emergency care
Pain medicine including:
The relief of post-operative pain
Acute pain medicine and the management of acute teams
Chronic and cancer pain management
The provision of sedation and anaesthesia for patients undergoing variousprocedures outside the operating theatre. Examples of this include different
endoscopic procedures, interventional radiology and dental surgery (this list
is not exclusive).
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Anaesthesia is the largest
single hospital specialty but is
probably the least well
understood. The general publichas little idea of the role of
anaesthetists, and, sadly,
the medical profession as awhole often mirrors this lack of
knowledge.
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ULTRASOUND
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What is ULTRASOUND
The frequency of range of sound above 20kHz is
known as ULTRASOUND
These waves inaudible to humans, can betransmitted in beams and used to scan the tissues of
the body.
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History
1500Leonardo da Vinci
1845Christian Doppler
1880Curie Brothers
1900Langevin 1927Wood & Loomis
19401950Ludwig, John Wild
1960Douglas Howry, Hertz & Elder
19701990New Developments
2000Now and the Future
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History of Ultrasound
ANAESTHESIA
1978La Grange P in 1978 described the use of
Doppler ultrasound for supraclaviclar brachial
plexus
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Development of Ultrasound
DMS
Diagnostic Medical
Sonography
An imaging tool thatis used to visualise
the soft tissue
structure of the body
by sending andreceiving signals to
and fro from the body
Acoustics
The science of
engineering and the
art of generating,propagating, and
receiving sound
waves
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Basic Ultrasound Physics
Transducer (AKA: probe)
Piezoelectric crystal
Emit sound after electriccharge applied
Sound reflected from
patient
Returning echo isconverted to electricsignalgray scaleimage on monitor
Echo may be reflected,transmitted or refracted
Transmit 1% and receive99% of the time
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Physics
Characterized by sound waves of high
frequency.
Higher than the range of Human Hearing
Sound waves are measured in Hertz (Hz)
Diagnostic U/ S = 1-20 MHz
Sound waves are produced by a transducer
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Monitor and Computer
Converts signal to an image/
archive
Tools for image manipulation Gainamplification of returning
echoes Overall brightness
Time gain compensation (curve) Adjust brightness at different depths
Freeze
Depth Zoom in for superficial view Zoom out for wide view
Depth limited by frequency
Focal zone
Optimal resolution wherever focal zone is
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Image controls
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Modes of Display
A mode
Spikeswhere precise length and depth
measurements are neededOphtho
B mode
M mode
Brightness used more often
- 2D construction of the image slide
Moving modemoving 1D image
Cardiac mainly
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Major Uses of Ultrasound
Obstetrics and Gynecology
Urology
Cardiology To observe structures or
functions of the hearth to
identify abnormalities.
To measure blood flow throughthe heart and major blood
vessels.
Lungs filled with air and ribs
limits the application.
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Modalities
X-ray Measures line integrals of attenuation
coefficient
CT Builds images tomographically; i.e. using a
set of projections
Nuclear Radioactive isotope attached to metabolic
marker
Strength is functional imaging, as opposed
to anatomical
Ultrasound Measures reflectivity in the body
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Comparison of modalitiesWhy do we need multiple modalities?
Each modality measures the interaction between
energy and biological tissue.
- Provides a measurement of physical properties oftissue.
- Tissues similar in two physical properties may differ
in a third.
Note:- Each modality must relate the
physical property it measures
to normal or
abnormal tissue function if
possible.
- However, anatomicalinformation and knowledge of a
large patient base
may be enough.
- i.e. A shadow on lung or chest
X-rays is likely not good.
Other considerations for multiplemodalities include:
- Cost
- Safety
- Portability / Availability
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Clinical Applications - Table
Chest Abdomen HeadX-Ray/
CT
+widely used
+CT - excellent
needs contrast
+CT - excellent
+X-ray - is good for bone
CT - bleeding, trauma
Ultrasound no,
except for+heart
+excellent
problems with
gas
poor
Nuclear +extensive use
in heart
Merge w/ CT +PET
MR +growing
cardiac
applications
+minor role +standard
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