INTRODUCTION TO ULTRASOUND
& REGIONAL ANESTHESIA
MBChB DA CABA & IC
Department of anesthesia/Al-yarmook Teaching Hospital
• The principle of Ultrasound
• rationale for US guidance.
• proper techniques of US guidance.
• interesting findings seen with US.
• specific nerve blocks
• Ultrasound waves are generated by piezoelectric
• 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.
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.
• 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.
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
Hyperechoic areas have a great
amount of energy from returning
echoes and are seen as white.
Hypoechoic areas have less energy
from returning echoes and are seen as
Anechoic areas without returning
echoes are seen as black.
- Ultrasound image of various tissues for
• Veins Anechoic/hypoechoic, non-
• Fat Hypoechoic, compressible
• Muscles Heterogeneous (mixture of hyperechoic
• lines within a hypoechoic tissue background)
• Tendons & Fascia Hyperechoic
• Bone Very hyperechoic with acoustic shadowing
• Nerves Hyperechoic below the
• clavicle/hypoechoic above the clavicle
• Air bubbles Hyperechoic
• Pleura Hyperechoic line
• Local anesthetic Hypoechoic, expanding hypoechoic region
• 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
• 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 sound in any
direction by rough surfaces or by
Scattering is the redirection of ultrasound in any direction caused by
rough surfaces or by heterogeneous media
• Attenuation is the loss of mechanical energy of
• 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 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
Tissues like nerves, tendons, and muscle exhibit
anisotropy , but most evident with tendon
• The transducer is scanning at a 90 degree angle.
The nerve (transverse view) is clearly visible.
Arrowhead = median nerve in the forearm
• The transducer is scanning at a 75 degree angle.
The nerve is still visible but less clear.
Arrowhead = median nerve in the forearm
• The transducer is scanning at a 45 degree angle.
The nerve is no longer visible.
Solution: angle the transducer slowly until the nerve comes
• 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 .
• Temporal resolution: depends on frame rate
• Two adjacent structures cannot be identified as separate entities on an
ultrasound scan if they are less than one wavelength apart.
• Types of Ultrasound transducer used in
• 1-linear :high frequency ,higher resolution
used for superficial tissues.
• 2-curved:low frequency ,lower resolution ,used
for deeper tissue
• Setting Depth
• Setting Gain
• Setting Focus
• Compound Imaging(sonoCT)
3- nerve and needle localization
Ultrasound machine controls
• Gain : the wave looses energy and become
attenuated deeper in tissue so time gain
compensation is required.
• Frequency:8-13 Mhz
• For shallow depth<4 cm use frequency>10
• For deeper structures >4cm preferably use
frequency <8 Mhz
• Reverberating artefacts : u/s wave is reflected back between tissue
interface so the retuning wave come late in time this will be
interpreted by the machine as distant signal.
• Mirror artefacts:
• Bayonet artefacts : the machine assumes the speed is constant at
• Comet tail artefact:usually at the pleural or peritoneal surface
• Acoustic enhancement artifacts :(e.g.blood vessels)
• Absent blood flow :small b.vessels cant be seen by colored doppler
this can be corrected by increasing the gain.
• Acoustic shadow: e.g. bone or pleura in supraclavicular block( the
area behind the bone is anechoic while hypoechoic in case of
Left : reverberating needle aretefact
middle : stone in the bladder with acoustic
enhancement behind the bladder & acoustic
shadow behind the stone
right : mirror image artefact of a haematoma .
Factors Reported to Inﬂuence
Needle Tip Visibility
• Angle of insonation
• Needle gauge
• Bevel orientation
• Receiver gain
• Needle motion and test injections
• Echogenic modiﬁcations
• Spatial compound imaging
• EZ guide (ezono 4000 ):it is based on magnetic identification of the needle
• Hydro Location Technique(0.5-1 ml)
• In animal models: a number of undesired effects, such as fetal weight
reduction, postpartum mortality, fetal abnormalities, tissue lesions, hind
limb paralysis, blood flow stasis, and tumor regression has been reported.
• It is easier to detect a needle with an echogenic tip. The figure
shows an example of the echogenic tip needle (Hakko™ Medical
Co. LTD Japan) with 3 hyperechoic dots at the needle tip (arrows).
complications of U/s guided
• Intravascular injection
Minimize it by:
1-careful needle visualization(especially the
tip of the needle)
2-aspiration before injection
• TREATMENT OF LOCAL ANESTHETIC
• 1) Airway, hyperventilation, 100% O2
• 2) Abolish convulsions (Diazepam, Midazolam,
• 3) Intralipids (1.5 mL/kg over 1 minute
(~100mL), then continuous infusion
• 0.25 mL/kg/min (~500 mL over 30 minutes)
• 4) CPR/ACLS, consider cardiopulmonary bypass
• the incidence of neurologic symptoms
following PNB varies depending on the
anatomic location, ranging from 0.03% for
supraclavicular blocks to 0.3% for femoral
blocks to up to 3% for inter-scalene blocks.
Fortunately, the vast majority of these
neuropathies appear to be temporary rather
than permanent neuropathy and resolve over
weeks to months.
• Suggested etiologies include mechanical trauma
from the needle, nerve edema and/or hematoma,
pressure effects of the local anesthetic injectate,
and neurotoxicity of the injected solutions (both
local anesthetics and adjuvants, e.g., epinephrine).
(3) Confounding factors that may play a role in
nerve injury include preexisting neuropathies
(e.g., diabetes mellitus), surgical manipulation,
prolonged tourniquet pressure, or compression
from postoperative casting.
Bioeffect and Safety
• ultrasound application could produce a biologic effect can
be characterized into two aspects: heating and mechanical.
• A modern ultrasound machine displays two standard
indices: thermal and mechanical. The thermal index (TI) is
defined as the transducer acoustic output power divided by
the estimated power required to raise tissue temperature by
1°C. Mechanical index (MI) is equal to the peak
rarefactional pressure divided by the square root of the
center frequency of the pulse bandwidth. TI and MI indicate
the relative likelihood of thermal and mechanical hazard in
vivo, respectively. Either TI or MI >1.0 is hazardous.
• Biologic effect is directly related to tissue exposure time
How to avoid nerve injury
• 1-inject LA under direct vision(of the needle tip and the
spread of LA after injection)
• 2- use a blunted bevel needle(or touhy needle)
• 3- don’t inject LA if the pt get severe pain or there is
• 4-idealy the pressure of the LA syringe should not exceed
• 5-nerve localization by elicitation of parasthesia and nerve
stimulation(current 0.3-0.5 mamp) alone is no more
recommended.(sometimes current as low as 0.2 ma
couldnot guarantee needle contact and on the contrary
currnts as high as 1.5 ma could not stimulate nerve when it
is in close contact with the nerve, as seen in animal model)
• American society of Regional
• Anesthesiologists Recommendations
• the following are the American society of Regional Anesthesiologists recommendations for
• 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
• 3. Confirm normal anatomy or recognize anatomic
• 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.
Set-up and Monitoring for Regional
All supplies located in this area must be readily identifiable and accessible to the anesthesiologist.
The area should be of ample size to allow block performance, monitoring, and resuscitation of
There should be equipment for oxygen delivery, emergency airway management, and suction, and
the area should have sufficient lighting.
A practically organized equipment storage cart is desirable and should contain all of the necessary
equipment (including equipment required for emergency procedures).
A selection of sedatives, hypnotics, and intravenous anesthetics should be immediately available to
prepare patients for regional anesthesia.
Emergency drugs (atropine, epinephrine, phenylephrine, ephedrine, propofol, thiopental,
succinylcholine, amrinone, intralipid) should also be immediately available.
During the performance of regional anesthesia, it is vital to have skilled personnel monitor the
patient at all times(electrocardiography, noninvasive blood pressure, pulse oximetry, and level of
consciousness of the patient should be gauged frequently using verbal contact because vasovagal
episodes are common with many regional procedures).
The patient should be closely observed for systematic toxicity(within 2 minutes for at least 30
minutes after the procedure).
Before performing blocks with significant sympathetic effects, a baseline blood pressure reading
should be obtained
Techniques for Brachial Plexus Blockade
• Interscalene Block
This block frequently spares the lowest branches of the plexus, the C8 and T1 fibers (which innervate the caudad
[ulnar] borderof the forearm).
Pneumothorax should be considered if cough or chest pain isproduced while exploring for the nerve (cupola of the
lungnear block site).
Direct injection into the vertebral artery can rapidly producecentral nervous system toxicity and convulsions.
The midpoint of the clavicle is identified. The subclavian arterypulse serves as a reliable landmark in thinner
individuals because the plexus lies immediately cephaloposterior to the subclavian artery.
Ultrasound imaging and nerve stimulation help avoid puncturing the pleura. There is a risk of pneumothorax
because the cupola of the lung lies just medial to the first rib; risk of pneumothoraxis greater on the right side
because the cupola of the lung is higher on that side; the risk is also greater in tall, thin patients.
This block provides excellent analgesia of the entire arm (blocks the musculocutaneous and axillary nerves more
consistently)and allows introduction of continuous catheters to provide prolonged postoperative pain relief.
There is a lower risk of blocking the phrenic nerve or stellate ganglion.
Vessel puncture is a potential complication.
Lateral needle insertion helps avoid the risk of pneumothorax.
This block is useful for surgery of the elbow, forearm, and hand(the musculocutaneous nerve may be blocked
This block is associated with minimal complications (neuropathy from needle puncture or intraneural injection of
• Andrew T. Gray, MD, PhD,ATLAS OF
ANESTHESIA 2nd edition,2013
• David L Brown , ATLAS OF REGIONAL
ANESTHESIA fourth edition ,2010
• Newyork School of regional anesthesia web