Reality n Myth - Anaesthetists and Ultrasound

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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Reality n Myth - Anaesthetists and Ultrasound