USG and its uses in anaesthesia practice

USG AND ANAESTHESIA
• PRESENTOR:Dr BHOOMIKA
• MODERATOR:Dr CHAITRA T S

• HISTORY
• In the twentieth century, the sinking of the Titanic followed by the
start of World War I served as catalysts for the development of sonar,
or sound navigation and ranging, which was the first real- world
application of the principles of sound.
• Karl Theodore Dussik, an Austrian psychiatrist and neurologist, is
credited as being the first physician to use ultrasound in medical
diagnostics when he attempted to visualize cerebral ventricles and
brain tumors using a primitive ultrasound device in 1942

INTRODUCTION
• A noninvasive procedure for visualising soft tissue structures of the
body ,by recording the reflection of high frequency sound waves
directed into tissues .
• USG has revolutionized the field of anaesthesia ,enabling
anaesthesiologist to perform procedures with greater precision and
safety .
• Allows visualisation of anatomical structures,nerves facilitating proper
needle placement and reducing the risk of complications.

Principle
• Sound waves are emitted by piezoelectric material, most often
synthetic ceramic material (lead zirconate titanate [PZT]), that is
contained in ultrasound transducers.
• When a rapidly alternating electrical voltage is applied to piezoelectric
material, the material experiences corresponding oscillations in
mechanical strain
• As this material expands and contracts rapidly, vibrations in the
adjacent material are produced and sound waves are generated.

Ultrasound Production
 Transducer produces ultrasound pulses (transmit 1% of the
time)
 These elements convert electrical energy into a mechanical
ultrasound wave
 Reflected echoes return to the scanhead which converts the
ultrasound wave into an electrical signal

• KEY PARAMETERS INCLUDE
• FREQUENCY
• WAVELENGTH
• VELOCITY
• POWER
• INTENSITY

FREQUENCY AND WAVELENGTH
• By definition, “ultrasound” refers to sound waves at a frequency
above the normal human audible range (>20 kHz).
• Frequencies used in ultrasonography range from 2 to 18 MHz.
• Frequency (f ) is inversely proportional to wavelength (λ) and varies
according to the specific velocity of FUNDAMENTAL PRINCIPLES OF
ULTRASOUND sound in a given tissue (c) according to the formula: λ =
c/f.

• Ultrasound waves with shorter wavelengths have higher frequency
and produce higher-resolution images, but penetrate to shallower
depths.
• Conversely, ultrasound waves with longer wavelengths have lower
frequency and produce lower-resolution images, but penetrate
deeper.

Reflection and propogation of sound waves depend on
• Acoustic impedence .
• Attenuation .

ACOUSTIC IMPEDENCE
• Propagation speed is the velocity of sound in tissues and varies
depending on physical prop- erties of tissues. Acoustic impedance is
the resis- tance to propagation of sound waves through tissues and is a
fixed property of tissues deter- mined by mass density and propagation
speed of sound in a specific tissue.
• For example, sound waves reflect in all directions, or scatter, at air-
tissue interfaces due to a large difference in acoustic impedance
between air and bodily tissues. Scattering of sound waves at air-tissue
interfaces explains why sufficient gel is needed between the transducer
and skin to facilitate propagation of ultrasound waves into the body

ATTENUATION
• As sound waves travel through tissues, energy is lost, and this loss of
energy is called attenuation.
• Attenuation is due to absorption, deflection, and divergence of sound
waves and is dependent on the attenuation coefficient of tissues,
frequency of sound waves, and distance traveled by sound waves.
• Absorption, the most important cause of attenuation, refers to
energy transferred from the ultrasound beam to tissues as heat.

PARTS OF USG MACHINE
• DISPLAY UNIT
• CPU
• KEYBOARD WITH CURSOR
• PRINTER
• TRANSDUCER
• STORAGE
• TRANSDUCER CONTROL

KEYBOARD WITH CURSOR
• Depth should be adjusted to position the structure
of interest in the center of the screen.
• Gain adjusts amplification of echoes returning to
the receiver. Appropriately adjusted gain is
important for accurate image interpretation.
• Increasing gain results in brighter images, and
decreasing gain results in darker images.
• Measurements and Calculations. Most ultrasound
machines have a caliper function to take
measurements.

TRANSDUCERS
• Ultrasound transducers are designed for optimal transmission and
reception of sound waves . An electrical shield lines the transducer
case to prevent external electrical interference from distorting sound
wave transmission.
• At the tip of the transducer, a thin matching layer improves efficiency
of sound wave transmission from piezoelectric elements to skin and
deeper structures.

• Backing material is an essential component of transducers. Backing
material is fixed behind the layer of piezoelectric elements to dampen
ongoing vibrations of elements.
• Sound energy is absorbed by backing material when elements are
generating and receiving sound waves.
• Transducers are sensitive instruments, and the internal components
of the transducer head, including the piezoelectric elements, can
break easily with minor impact. Providers must be trained to
safeguard transducers at all times.

• There are four basic types of transducers: linear, curvilinear, phased-
array, and intracavitary

• linear transducers generate high-frequency (5–10 MHz), shorter-
wavelength sound waves with excellent axial and lateral resolution.
Linear transducers also have excellent elevational, or slice thickness,
resolution because ultrasound beam shape is relatively flat.
• Linear transducers are limited to visualization of superficial structures
in a relatively narrow field of view because attenuation decreases
resolution and penetration at depths >5 cm.
• Linear-array transducers are ideal for evaluating superficial structures,
including eyes, blood vessels, muscles, nerves, and joints, and for
performing ultrasound-guided procedures.

• Curvilinear transducers utilize lower frequencies (2–5MHz) with
longer wavelengths that penetrate deep structures with relatively less
attenuation, particularly for structures 5–25 cm deep.
• Curvilinear transducers are ideal for imaging intraabdominal organs,
including liver, spleen, kidneys, and bladder, and for imaging larger
musculoskeletal structures, such shoulders and hips.

• Phased-array transducers combine a low- frequency ultrasound beam
(1–5MHz) with a small, triangular-shaped footprint with adjust- able
focusing and steering.
• Phased-array technology allows for more efficient two-dimensional
imaging and is ideal for moving structures, such as the heart.
• Intracavitary transducers combine a small, micro-convex footprint
with a high frequencyrange (5–8MHz).
• Intracavitary transducers are ideal for transvaginal and transrectal
ultrasound and also for intraoral evaluation of peri- tonsillar abscess.

• 3D/4D TRANSDUCERS :
• Capable of obtaining volumetric data
• Used in obstretic and fetal
imaging ,gynecology,vascular studies
• INTRAOPERATIVE TRANSDUCERS :
• Sterlisable and designed for use in surgical
procedures.
• WIRELESS TRANSDUCERS :
• Enable flexibility during scanning and
enhance portability.

NEEDLE ORIENTATION
-Using a longitudinal approach, the
transducer is placed lengthwise
along the long axis of the target
vessel.
-A transverse view of a vessel can
be obtained by placing the
transducer perpendicular to the
long axis of the vessel

ECHOGENICITY
• Two-dimensional (2-D) mode is the default mode of most ultrasound
machines, and the majority of bedside diagnostic ultrasound imag-
ing is performed in 2-D mode. This mode is also called B-mode, for
“brightness,” because echogenicity, or brightness, of observed struc-
tures depends on the intensity of reflected signals.
• Structures that transmit all sound waves without reflection are called
anechoic and appear black on ultrasound. Most fluid-filled structures
appear anechoic.

• Structures that reflect some sound but less than surrounding struc-
tures appear hypoechoic, whereas structures that reflect sound
waves similar to surrounding structures appear isoechoic.
• Both hypoechoic and isoechoic structures appear as shades of gray
and are generally soft tissue structures.
• Hyperechoic structures reflect most sound waves and appear bright
white on ultrasound. Calcified and dense structures, such as the
diaphragm or pericardium, are hyperechoic.

MODES IN ULTRASOUND
• B-mode (brightness) is the main mode of any ultrasound machine.
Each gray scale tomographic image in B-mode is composed of pixels
with brightness depending on the intensity of the echo that is
received from the corresponding location in the body. This mode is
used to evaluate and scan organs in real time

Modes in ultrasound
• M-mode, or “motion” mode, is an older mode of imaging but is still
frequently used today to analyze movement of structures over time.
• After a 2-D image is acquired, M-mode imaging is applied along a single line
within the 2-D image.
• A single-axis beam is emitted along a select line and gathers data on
movement of all tissues along that line. All points on the line are plotted
over time to evaluate the dimen- sions of cavities or movement of
structures.
• M-mode is used to measure the size of cardiac chambers or movement of
cardiac valves throughout the cardiac cycle.
• measurement of change in inferior vena cava diameter with respiration, and
evaluation of the lung-pleura interface to rule out pneumothorax.

• The Doppler effect is a shift in frequency of sound waves due to
relative motion between the source and observer.
• Blood flow moving toward the transducer shifts the echoes to a
higher frequency while blood flow moving away from the transducer
shifts the echoes to a lower frequency.
• The change in frequency between the emitted and received sound
waves is called Doppler shift.
• Variables that determine the amount of Doppler shift are:1.
Frequency of ultrasound beam 2. Velocity of blood flow 3. Angle of
insonation

Applications of USG in Anesthesia .
1.Regional anesthesia .
2.Nueraxial and chronic pain procedure .
3.Vascular access.
4.Airway assessment.
5.Lung ultrasound .
6.Ultrasound neuro-imaging .
7.Gastric ultrasound .
8.Focused transthoracic echo (TEE)
9.Transeosophageal echo.

VASCULAR ACCESS
• Advantages of ultrasound-guided central venous catheterization include
identification of the vein, detection of variable anatomy and intravascular
thrombi, and avoidance of inadvertent arterial puncture. It is safer and
less time consuming than the traditional landmark technique.
• Ultrasound can also be used for localization of central vein catheters and
detection of postprocedural pneumothorax, as an alternative to chest
radiography.
• Ultrasound arterial cannulation helps in reducing the number of
attempts, shortening the procedure time, and increasing the success
rate, even in children

VASCULAR ACCESS
ARTERIES VEINS
NONCOMPRESSIBLE UNDER
LIGHT PRESSURE
COMPRESS EASILY UNDER
LIGHT PRESSURE
THICK,ECHOGENIC WALLS THIN,NEARLY
IMPERCEPTIBLE WALLS
ROUND SHAPE VARIABLE SHAPE
PULSATILE NONPULSATILE
COLOR FLOW UNCHANGED
WITH DISTAL
COMPRESSION
COLOR FLOW AUGMENTED
BY DISTAL COMPRESSION

RADIAL ARTERY CANNULATION
• The radial artery is the most common
site for arterial cannulation.

NEURAXIAL AND CHRONIC PAIN PROCEDURE
• Ultrasound has become a commonly used modality in the performance of chronic pain
interventions and has begun to substitute for CT scans and fluoroscopy in many chronic
pain procedures.
• neuraxial block
• nerve root blocks (e.g., cervical and lumber);
• stellate ganglion block;
• lumbar transforaminal injections for radicular pain,facet joint block
• Epidural blood patch
• Intra-articular joint injections;usg guidance for peripheral nerve stimulator implantation
• Interventional procedures for patients with chronic pelvic pain (e.g., pudendal neuralgia,
piriformis syndrome, and “border nerve” syndrome).

AIRWAY ASSESSMENT
• Airway ultrasound can visualize and
assess the tongue, oropharynx,
hypopharynx, epiglottis, larynx, vocal
cords, cricothyroid membrane, cricoid
cartilage, trachea, and cervical
esophagus
• The posterior pharynx, posterior
commissure, and posterior wall of the
trachea cannot be visualized due to
artifacts that are created by the
intraluminal air column.

AIRWAY ASSESSMENT
• 1)prediction of difficult airway
• 2)confirmation of proper endotracheal tube placement and ventilation;evaluation
of airway pathologies that may affect the choice of airway management (e.g.,
subglottic hemangiomas and stenosis), or mandate urgent securing of airway (e.g.,
Epiglottitis)
• 3)prediction of obstructive sleep apnea
• 4)prediction of size of endotracheal, endobronchial, and tracheostomy
tubes;airway related nerve blocks;assessing and guidance for proper percutaneous
dilatational tracheostomy (PDT)
• 5)prediction of successful extubation:a)prediction of airway edema;b)assessment
of the diaphragm movement; c)assessment of vocal cord movements.

• Confirmation of proper endotracheal tube placement
can be done by two methods, direct and indirect .
• One direct method is the use of a real-time
ultrasound probe placed transversely on the neck at
the level of the suprasternal notch during intubation
to observe whether the tube enters the trachea or
esophagus.
• An indirect method is by observing bilateral lung
sliding with ventilation as the probe is placed in the
midaxillary line.

• Diagnosis and prediction of obstructive sleep apnea is a challenge, as
many patients come for surgery undiagnosed. tongue base width,
measured by ultrasound, may influence the severity of obstructive sleep
apnea.
• In percutaneous dilatation tracheostomy , identification of possible
vessels in the field and localization of the midline and the tracheal rings
for optimal intercartilaginous space selection, to avoid any possible
laryngotracheal stenosis.
• Predication of successful of extubation , the air-column width during cuff
deflation at the level of the cricothyroid membrane is a potential
predictor of postextubation stridor that reflects laryngeal edema.

ULTRASOUND NEUROMONITORING
• Elevated intracranial pressure (ICP) requires special precautions by the
anesthesiologist, such as avoiding particular medications, ventilation settings, and
neuraxial anesthesia.
• Neuroultrasound are as follows:
• 1)optic nerve sheath diameter (ONSD) measurement
• 2)transcranial Doppler ultrasound (TDU)
• 3)pupillary light reflex (PLR).
• Measurement of optic nerve sheath diameter (ONSD) has been found to reflect
intracranial pressure, as an increase in ICP will be transmitted through the
subarachnoid space that surrounds the optic nerve within its sheath and has been
proposed as noninvasive and reliable means of assessing ICP in neurocritically ill
patients

• Usually optic nerve sheath measured 3mm .
• ONSD of more than 5.00 to 5.70 mm has a
concurrent ICP value above 20 mm Hg.
• In Intracranial hypotension, as in a setting of dural
leak, might be associated with decreased ONSD, as
the optic nerve is surrounded by cerebrospinal fluid
and dura mater, which form the optic nerve sheath.

GASTRIC ULTRASOUND
• A full stomach may lead to aspiration pneumonia and subsequent
morbidities.
• Anesthesiologists may encounter patients with unknown prandial status,
and even fasting “sufficient” time cannot guarantee an empty stomach in
many cases (e.g., in the elderly or in patients with gastroparesis)
• Current and potential applications of Gastric ultrasound are as follows:
• 1)assessment of gastric content and diagnosis of full stomach
• 2)confirmation of gastric tube placement.
• 3)Evaluate the imaging findings associated with an empty stomach, liquid
in the stomach, and solid food in the stomach.

• If the stomach contains only clear liquids, the
volume can be estimated by measuring the CSA
of the antrum at the level of the aorta.
• The volume of stomach contents (in milliliters)
can be estimated by the following equation:
• 27 + (14.6 * CSA) – (1.28 * age)
• Gastric volumes <1.5 ml/kg are considered
normal (consistent with baseline secretions),
associated with a low risk of aspiration under
anesthesia. Volumes greater than 1.5 ml/kg are
treated as positive findings.

LUNG ULTRASOUND
• Critical care providers have
adopted the bedside lung US
in emergency (BLUE) protocol
as a standardized approach to
lung US in the ICU

NORMAL LUNG AERATION PATTERNS
• “Lung sliding” signs are sliding of visceral and parietal layers
of pleura with respiration.
• Seashore sign is a complex picture of parallel lines signifying
the static thoracic wall and sandy “granulous” pattern, which
reflect the normal pulmonary parenchyma.
• A-lines are a basic artifact of normally aerated lung.

PATHOLOGICAL LUNG SIGNS
• B-lines represent discrete laser-like vertical hyperechoic lines that
arise from the pleural line and extend to the bottom of the screen.
These lines are consistent with interlobular pulmonary edema and
can be found in both ARDS and cardiogenic pulmonary edema.
• Dynamic and static air bronchograms which consist of
hyperechoic punctiform elements within the lung parenchyma can
be used to diagnose consolidation and atelectasis, respectively.
• Lung pulse is an early and dynamic diagnostic sign of complete
atelectasis, in which US perceives the vibrations of heart activity,
along with the absence of lung sliding

PULMONARY EDEMA AND FIBROSIS
• When the pulmonary interstitium
thickens (secondary to fibrosis or
fluid), B-line artifacts replace the
normal A-lines
• B-line artifact consists of well-
defined, laserlike, vertical,
echogenic lines arising from the
pleural line and extending to the
bottom of the image.

PNEUMOTHORAX
• Identification of a lung point on lung US yields 100% specificity
for pneumothorax
• normal pattern is called the seashore sign as it depicts the
boundary between the stationary chest wall (“ocean”) and
moving lung (“sand”)
• When a pneumothorax is examined at M-mode US, the smooth
horizontal lines are uninterrupted, as the chest wall and air
deep to the pleura are both stationary in pneumothorax
• This appearance of pneumothorax at M-mode examination has
been dubbed the bar code sign

• SEASHORE SIGN-NORMAL LUNG • BARCODE SIGN -
PNEUMOTHORAX

PLUERAL EFFUSION
• Simple effusions commonly present as anechoic fluid in the posterior
dependent lung

REGIONAL ANAESTHESIA
• Single-injection ultrasound-guided nerve blocks are ideal to relieve pain
from acute injuries and painful procedures.
• Common indications include wound debridement andirrigation, laceration
repair, incision and drain- age, fracture reduction, and joint relocation.
• Patient Selection :Single-injection ultrasound-guided nerve blocks should
be performed only in patients who are awake, alert, and able to cooperate
with a neurologic exam.
• Patients with preexisting neurologic deficits are not candidates for
ultrasound-guided nerve blocks because the presence of peripheral nerve
injury (PNI)

REGIONAL ANAESTHESIA
• CENTRAL NEURAXIAL BLOCKADE

• EPIDURAL BLOCKADE CAUDAL EPIDURAL BLOCKADE

PERIPHERAL NERVE BLOCK
• SUPRACLAVICULAR BLOCK

SUPRACLAVICULAR BLOCK PARA-SAGITTAL OR OBLIQUE
CORONAL PLANE
HYPOECHOIC HOLES SUPERIO-
POSTERIOR TO SUBCLAVIAN
ARTERY (TRUNKS,DIVISIONS)
INTERSCALENE BLOCK OBLIQUE C6 LEVEL INTERSCALENE FOLLOW STERNOCLEOID MASTOID
MUSCLE LATERALLY HYPOECHOIC
BUBBLES ,BETWEEN SCALENES
ANTERIOR/MEDIUS
FEMORAL BLOCK HORIZONTAL PLANE AT INGUINAL
LIGAMENT LEVEL
M->L,VEIN/ARTERY/NERVE

FOCUSED ASSESSED TRANSTHORACIC
ECHO(FATE)
• This approach basically involves four standardized acoustic views for
cardiopulmonary screening and monitoring.FATE was introduced by
Jensen et al for cardiopulmonary monitoring in the intensive care unit
• Focused cardiovascular ultrasound performed by anesthesiologists in
the perioperative period accurately detects major cardiac pathology
and significantly alters perioperative management.

IVC ASSESSMENT FOR FLUID
RESPONSIVENESS
• In spontaneously breathing patients,
• a. IVC measuring < 2 cm in diameter coupled with IVC collapse> 50%
with each breath
• b. IVC collapsibility > 12%
• IVC collapsibility = (max diameter – min diameter) / (mean
diameter) x 100

• In mechanically ventilated patients who are passive on the ventilator,
fluidresponsiveness is likely if
• IVC distensibility > 18%.
• IVC distensibility = (max diameter – min diameter) / (min diameter) x
100

FOCUSED ABDOMINAL SONOGRAPHY IN
TRAUMA (FAST)
• The primary objective of focused abdominal sonography in trauma
(FAST) - to identify the presence of haemoperitoneum
• Indications of FAST
• Haemodynamically unstable patients with suspected abdominal
injury.
• Significant extra-abdominal injuries (orthopaedic, spinal, chest)
requiring a non-abdominal emergency surgery.
• The presence of free intraperitoneal fluid or solid organ injury is
considered as a positive FAST .

SUMMARY
• Ultrasound is a unique tool which provides the anaesthesiologist with
diagnostic and monitoring capabilities enabling optimization of
perioperative management.
• Procedural anaesthesia applications in the field of anaesthesiology
are numerous and improve the quality of care.
• Ultrasound can be the third eye of the anaesthesiologist that helps in
the performance of previously blind procedures.

RECENT ADVANCES
• Echogenic needles are customized needles that improve the
ultrasound beam's reflection to enhance needle visualization in an
ultrasound image.
• The SonixGPS needle guidance system (Ultrasonix, Richmond, BC,
Canada) is a GPS technology with a new needle tracking system, using
sensors in both the needle and transducer to obtain a real-time image
of needle shaft and tip position related to the ultrasound beam that is
based on the needle trajectory.

REFERENCES
• https://pmc.ncbi.nlm.nih.gov/articles/PMC3856172/
• POINT OF CARE ULTRASOUND -ELSEVIER

USG and its uses in anaesthesia practice

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