Ultrasonography is useful for regional anesthesia procedures. It allows visualization of key anatomical structures like nerves, blood vessels, muscles and bones. There are different ultrasound imaging modes used including B-mode, M-mode and Doppler. Factors like frequency, depth and gain affect image resolution. The needle can be inserted in-plane or out-of-plane relative to the ultrasound beam. Proper scanning technique and following guidelines help ensure safe and effective ultrasound-guided regional anesthesia.

1. ULTRASONOGRAPHY IN ANAESTHESIOLOGY
SPEAKER: DR. RAJESH CHOUDHURI,PGT
MODERATOR: DR. B. SUTRADHAR, ASST. PROF
DEPT. OF ANAESTHESIOLOGY, AGMC& GBP HOSPITAL

2. USG image generation
• Ultrasound waves are generated by piezoelectric crystals.
• The piezoelectric crystals convert the mechanical energy of the returning
echoes into an electrical current, which is processed by the machine to
produce a two-dimensional grayscale image that is seen on the screen.
• Audible sounds spread out in all directions, whereas ultrasound beams are
well collimated
• The machine spend 100x time to listen to returning echos compared to sent
ones.

3. Ultrasound Image Modes
• A-mode : the oldest mode(1930), a simple one- dimensional ultrasound
image is generated as a series of vertical peaks corresponding to the
depth of the structures at which the ultrasound beam encounters
different tissues.

4. • B Mode : a two dimensional mode and provide a cross sectional image
through the area of interest and is the primary mode currently used in
regional anesthesia.
• M mode(motion) : one dimensional mode against time mostly used for
cardiac imaging.
• B mode image M mode image

5. • Doppler mode: measures the shift in the frequency between the
incident and the reflected wave after hitting a moving object.
• Colour -flow: the probe should be slightly tilted to be near the long
axis of the vessel. Blood coming toward the probe appears red and
appear blue if it is moving away from the probe , increasing gain
improves view for smaller vessels.
• Pulsed doppler : Continuous doppler.

6. DOPPLER COLOUR FLOW MAPPING

7. ECHOGENICITY
• Hyperechoic areas have a great amount of energy from
returning echoes and are seen as bright &white.
• Hypoechoic areas have less energy from returning
echoes and are seen as dark gray and black.
• Anechoic areas without returning echoes are seen as
black.

9. Ultrasound image of various tissues for regional anesthesia
• Veins : Anechoic/hypoechoic, non- pulsatile ,compressible, vary in size
with respiration.
• Arteries: Round in cross section, pulsatile not easily compressible.
• Fat: Hypoechoic, compressible.
• Muscles: Heterogeneous (mixture of hyperechoic lines within a
hypoechoic tissue background)
• Tendons & Fascia: Hyperechoic .
• Bone : Very hyperechoic with acoustic shadowing behind.
• Nerves: Honeycomb structures with hypoechoic fascicles surrounded by
hyperechoic tissues.
• Air bubbles: Hyperechoic .
• Pleura : Hyperechoic line.
• Local anesthetic : Hypoechoic, expanding hypoechoic region.

10. A sonogram showing a round anechoic artery
(A) and an oval shaped anechoic vein (V); a vein
is collapsible while an artery is not.
Fat has a hypoechoic background containing streaks
of hyperechoic lines that are often irregular in
texture and length; the fat layer is most superficial;
note the difference in appearance between fat and
muscle.

11. Muscle also has a hypoechoic background containing
short streaks of hyperechoic lines; the outline of a
muscle layer (the fascial sheath) is highly
hyperechoic. Bone often shows a hyperechoic
outline (arrows) and a hypoechoic bony shadow
underneath due to a lack of beam penetration.
A nerve (arrowhead, N) and a tendon (arrow,
T) of the forearm in cross section; the nerve is
oval and the tendon has an irregular shape;
note that the tendon will merge into a muscle
proximally while the nerve does not.

12. A nerve in longitudinal section (arrowheads)
showing internal echotexture consisting of
continuous hypoechoic longitudinal elements
(fascicle groups) interspersed with hyperechoic
perineural connective tissues.
A tendon in longitudinal section (arrows); a tendon
appears very much like a nerve in this view
although the tendon has a fibrillar internal
echotexture and discontinuous hyperechoic
speckles.

13. A hypoechoic nerve root (arrowhead) in the low
interscalene region; nerves are generally
hypoechoic in the interscalene and supraclavicular
regions; the hypoechoic component represents
the neural tissue.
Nerves below the clavicle and in the lower limbs
are predominantly hyperechoic and have a
honey comb appearance. For example, the
median nerve in the elbow region (arrowhead) is
predominantly hyperechoic. The degree of
hyperechogenicity likely reflects the amount of
connective tissue within the nerve.

14. REFLECTION
• Reflection occurs at the boundary or interface of different types of tissue.
The reflection is inversely related to water content of tissue .
• Substances low in water content or high in materials that are poor sound
conductors (e.g., air, bone) reflect almost all the sound and appear very
bright.
• SCATTERED VERSUS SPECULAR REFLECTION
• • In specular reflection incident angle equals the reflected angle & usually
the reflection is from smooth surface(e.g. needle ,diaphragm or blood
vessels , pleura and peritoneum).
• . Scattering is the redirection of ultrasound in any direction caused by
rough surfaces or by heterogeneous media

15. ULTRASOUND WAVE INTERACTION WITH TISSUES
•Reflection
• SPECULAR (large smooth
objects like a needle) (d)
• SCATTERING (most
neural images) (a)
•Refraction (c)
•Transmission (b)

16. ATTENUATION
• Attenuation is the loss of mechanical energy of ultrasound.
• About 75% of the attenuation is caused by conversion to heat.
• The amount of attenuation directly related to:
1-distance travelled .
2-wavelength used.
3-attenuation coefficient of tissue.
• Anisotropy :Anisotropy means that the backscatter echoes from a
specimen depend on the directional orientation within the sound field.
Anisotropy can be quantified by specifying the transducer frequency and
the decibel change in backscatter echoes with perpendicular and parallel
orientation of the specimen. Tissues like nerves, tendons, and muscle
exhibit anisotropy , but most evident with tendon.

17. Overcoming Loss of Signal from Attenuation
• Artificial Enhancement
(Adjusting Gain)
• Time Gain Compensation
• Adjusts gain independently
at specified depth intervals
• Most modern U/S machines
do this automatically
(autogain)
• Choosing lower frequencies
for deeper tissues (posterior
sciatic)

18. RESOLUTION
• Resolution, the ability to distinguish two close objects as separate.
• • Axial resolution : the minimum separation of above-below planes along
the beam axis. It is determined by spatial pulse length:
Axial resolution = wavelength (λ) × number of cycle per pulse (n) ÷ 2
• Lateral resolution: is a parameter of sharpness to describe the minimum
side-by-side distance between two objects. It is determined by both
ultrasound frequency(higher frequency decreases beam width so it
improves lateral resolution) .Beam width can be determined with focusing
the ultrasound beam to the target

20. Types of Ultrasound transducer used in regional anesthesia
1-linear: high frequency
,higher resolution used for
superficial tissues.
2-curved: low frequency
,lower resolution ,used for
deeper tissue

21. FACTORS DETERMINING RESOLUTION
• 1-Machine Setting:
• Setting Depth
•Setting Gain
•Setting Focus
•Compound Imaging(sonoCT)
• 2-transducer handling: Transducer movement Transducer orientation.
• 3- nerve and needle localization.

22. Ultrasound machine controls
• • Gain : the wave looses energy and become attenuated
deeper in tissue so time gain compensation is required.
• • Depth
• • Frequency:8-13 Mhz
• For shallow depth<4 cm use frequency>10 MHz.
• For deeper structures >4cm preferably use frequency
<8 Mhz

23. All Ultrasound Guided Blocks Involve Three Steps
•Choosing One of Two Imaging Views
• Short Axis View
• Long Axis View
•Scanning the Nerve Track for Image
Optimization
•Choosing a Needle Approach Technique
• In Plane
• Out of Plan

24. Imaging Plane Options
• Long Axis View or Longitudinal View
• Rarely Used
• Short Axis View or Transverse View
• Most Commonly Used
• Relatively Easy
• Better Resolution of Fascial Barriers that Surrond Nerves
• Dynamic Assessment of Circumferential Local Anesthetic Spread
• Workable Image Even with Slight Movement of Transducer Probe

25. The ART of Scanning
• Alignment:
Sliding Movement of Trandsducer Along the Course of the Nerve
Lengthwise (Used in Short Axis View).
• Rotation:
Clockwise/Counterclockwise Transducer Movement (Particularly
important when attempting a long axis view).
• Tilting:
Angling Movement of Transducer to Optimize the Angle of
Incidence (90º).

26. Where is The Needle Coming From?
• Out of Plane Technique: Inserting the needle so that it crosses the plane of
imaging near the target.
• In Plane Technique: Inserted within the plane of imaging to visualize the entire
shaft and tip.

27. • Disadvantages
• Out of Plane Technique
• Unable to accurately track needle tip
• Difficulty finding the echogenic “dot”
as the needle crosses the US beam.
• In Plane Technique
• More Time Consuming
• More difficult to perform
• False security when partial needle
lineups give appearance of a needle
tip
• Can be more painful secondary to
longer insertion paths
• Advantages
• Out of Plane Technique
• Shorter Needle Insertion Paths
• Less Patient Discomfort
• Easier to Perform
• In Plane Technique
• Ability to Track the Needle Tip
• Theoretically Safer

28. American society of Regional Anesthesiologists recommendations for
performing an ultrasonography-guided block
• 1.Visualize key landmark structures including muscles, fascia, blood vessels, and bone.
• 2. identify the nerves or plexus on short-axis imaging, • with the depth set 1 cm deep to the
target structures.
• 3. Confirm normal anatomy or recognize anatomic variation(s).
• 4. Plan for the safest and most effective needle approach.
• 5. Use the aseptic needle insertion technique.
• 6. Follow the needle under real-time visualization as it is advanced toward the target.
• 7. Consider a secondary confirmation technique, such as nerve stimulation.
• 8.When the needle tip is presumed to be in the correct position, inject a small volume of a
test solution.
• 9. Make necessary needle adjustments to obtain optimal perineural spread of local
anesthesia.
• 10. Maintain traditional safety guidelines of frequent aspiration, monitoring, patient
response, and assessment of resistance to injection.