ultrasound

1. Amare H.
Ultrasound guided regional
anesthesia
US guided Hernia block & TAP

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

11. Image optimisation
 By adjusting the machine pre-set, depth,
gain and focus

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

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

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)