2. Principles of US guided regional
anesthesia
Four components
Image capture
Image optimization
Image interpretation
Needling technique
3. Image capture
Knowledge of Machine capabilities
Transducer characteristics
How to handle the transducer
Multifunctional, Range of transducer
frequencies, Doppler, Specific pre-sets
(Nerve & Vascular) & enhanced image
processing
4. Transducers
The most commonly used probe is a high-
frequency, linear array probe (5–10 MHz)
This gives good spatial resolution for the
nerves and plexuses, which are usually
superficial (1–5 cm deep)
A low frequency curvilinear probe (2–5
MHz) can be useful for deeper nerves and
plexuses,
but it is limited by its poor spatial
resolution at increasing depth.
5. Linear VS Curved Array
transducers
Transducer Frequency &
depth of view
Field of view Application
Linear Array 13 – 6MHz
6.0cm
Beam width
38mm
Rectangular
Field of view
Brachial Plexus
Femoral NB
Distal Sciatic
NB
Curved Array 5 – 2 MHz
30cm
Beam width
60mm
Wide field of
view
Sciatic NB
Spine
Lumbar Plexus
Infraclavicular
BPB
6. Scanning technique
Orient the transducer with screen
Orientation marker on the edge of the transducer
Highlighted green dot
Place the transducer lightly on the skin –
image display
Hand movement – PART
Pressure, Align, Rotate & Tilt
7. Hand Movement - PART
Pressure – Apply optimum pressure with
transducer on the skin
Ensure not to distort anatomy
Identification of blood vessels possible
Veins – Compressible
Arteries – Non- Compressible
8. Hand Movement - PART
Align (Slide) – Movement across the surface
of the skin
Follow the nerve and other structure – MCN
– Head of Humerous
Identify optimal entry point for injection
9. Hand Movement - PART
Rotate – twisting movement
Obtain short axis view
Tilt – Rocking hand movement (heal/toe)
Optimize the angle of insonation
(anisotropy)
Adjust for varying depth of the nerve
/structure
10. Planes of view
Short axis – Transverse
Long axis – Longitudinal
12. Image interpretation
“You only see what you know”
Understanding of different tissue
echogenicity
Recognition of artefacts
Effective use of Doppler
13. Peripheral nerves
Peripheral nerves consist of a collection of
axons arranged in to fascicles, within
variable amount of connective tissue
The amount of connective tissue increases
the more the distal the nerve from CNS –
alters the US appearance – Hyperechoeic
14. Peripheral nerves
Fascicles of peripheral nerves can be
detected with high-resolution ultrasound
imaging
This fascicular echotexture is the most
distinguishing feature of nerves
(“honeycomb” architecture)
15. More central nerves, such as the cervical
ventral rami, have fewer fascicles and
therefore can appear monofascicular on
ultrasound
Slide a broad linear transducer over the
known course of a peripheral nerve with the
nerve viewed in short axis
16.
17. Nerves can be round, oval, or triangular
Although nerve shape can change along the
nerve path, the cross-sectional nerve area
is constant in the absence of major
branching
Peripheral nerves are pathologically enlarged
by entrapment or in certain neuromuscular
disorders such as Charcot-Marie-Tooth
disease type IA
18. There is some evidence to suggest that
patients with diabetic neuropathy also have
enlarged peripheral nerves
19. Although direct nerve imaging has led to a
phenomenal increase in ultrasound-guided
regional anesthesia,
the identification of other nearby
structures (e.g., fascia and other
connective tissues) also is critical
20. Block Needles for Ultrasound-
Guided Procedures
Metal needles are hyperechoic and can
cause reverberation artefact
Needle tip visibility is best when the needle
path is parallel to the active face of the
transducer
In-plane (IP) or Out of –Plane (OOP)
21. In plane
Needle visualised in its entire length
Good visibility of Needle- Nerve interface
22.
23.
24.
25. Out of plane
Familiar needle insertion point
Short skin – nerve distance
Minimal intramuscular needle passage
Needle seen as a dot when in US beam (Be
aware tip and shaft is similar)
Editor's Notes
Ideal characteristics of the ultrasound machine
Gain – Brightness / Contrast
Sliding through the course of the nerve will identify the nerve
A, Fascicles of the median nerve in the forearm. In this sonogram the “honeycomb” appearance of a polyfascicular peripheral nerve is observed. B, Monofascicular echotexture of the brachial plexus in the neck
Sonogram of the popliteal fossa of a patient with Charcot-Marie-Tooth disease type 1A. The peripheral nerves are markedly enlarged because of the large fascicles
In this sonogram, the ulnar nerve and ulnar artery are viewed in short axis in the forearm. The nerve is surrounded with anechoic local anesthetic
The in plane approach appears easiest for clinicians starting US since the needle is easily visualised
Ilioinguinal block with ultrasound guidance (in-plane approach).
Abdominal wall imaging for ilioinguinal nerve block. A, In this sonogram, the external oblique, internal oblique, and transversus muscles are identified (the “three-layer cake” appearance). The ilioinguinal nerves are seen between the internal oblique and transversus muscles. B, The “kayak” sign of successful ilioinguinal injection. The fascia between the internal oblique and transversus muscles is split apart in the shape resembling a kayak
Abdominal wall imaging for ilioinguinal nerve block. A, In this sonogram, the external oblique, internal oblique, and transversus muscles are identified (the “three-layer cake” appearance). The ilioinguinal nerves are seen between the internal oblique and transversus muscles. B, The “kayak” sign of successful ilioinguinal injection. The fascia between the internal oblique and transversus muscles is split apart in the shape resembling a kayak
Axillary block with ultrasound guidance (out-of-plane approach). A, External photograph of the approach. B, Sonogram of the neurovascular bundle in short-axis view with the needle tip crossing the plane of imaging