BY
KARIM YOUSSEF KAMAL, MD
Lecturer of Anesthesia, Intensive
Care and Pain Management
AIN SHAMS UNIVERSITY
Definition:
A peripheral nerve block (PNB) is the
injection of a local anesthetic around a
nerve or group of nerves with blockade of
nerve impulse conduction, causing
temporary analgesia and loss of sensory
and motor function.
 More
hemodynamic stability compared
with neuraxial blocks.
 Anticoagulation less of an issue.
 Increasing popularity due to advances in
ultrasound technology.
 Introduction of perineural catheters
prolongs post-operative pain control
benefits.
 Avoidance
of general anesthesia
Primary regional anesthetic vs. combination
with “light” general anesthetic.
 Most patients request intra-operative
sedation.
 Decreased PONV, sore throat, delirium,
airway obstruction and respiratory
depression.
 Decreased time to discharge from PACU.
 Increased patient satisfaction.

 Post-operative
pain control
Decreased narcotic requirements and
associated adverse side effects (e.g.
nausea, pruritis, sedation, confusion,
respiratory depression).
 Earlier recovery of bowel function.
 Improved tolerance of physical therapy.
 Improved pain scores in PACU.
 Increased patient satisfaction.

 Infrastructure
requirements and potential for
surgeon delays.
 Failed Blocks.
 Intraoperative awareness and non-operative
discomfort (e.g. positioning).
 Variable duration (approx. 4-40 hours).
 Rare serious complications (e.g. local
anesthetic toxicity, nerve injury).
Ester
type:
unstable, broken
down by
pseudocholine
esterase.
Amide type:
stable, broken
down be liver
enzymes
Ester types
Amide types
Cocaine
 Lidocaine
Procaine
 Mepivacaine
Chloroprocaine
Tetracaine
benzocaine
Ester types
 Prilocaine
 Etidocaine
 Bupivacaine
 Levobupivacaine
 Ropivacaine
•Deposition
of solution near nerves.
•Permeation
of nerve axons.
•Binding
to sites in voltage gated Na
channels.
•Affection
of nerve conduction.
1)
2)
3)
4)
5)
6)
7)
Protein binding: determines amount of free
active part.
Clearance: ester type depend on cholinesterase
while amide type on hepatic blood flow.
Cardiac disease: ↓ COP→ ↓distribution.
Liver disease: ↑ blood level of amide type.
Renal disease: minimal effect.
Newborn: immature liver.
Old age: ↓ dose
 Epinephrine:
↑duration, ↑ intensity, ↓systemic
absorption. Also allowes early detection of I.V
injection.
 Steroids: antiinflammatory & analgesic effect.
 Ketamine: NMDA anatagonist→analgesia.
 Hyaluronidase: breaks collagen→ greater spread.
 Clonidine: direct inhibition of nerve conduction
plus indirect analgesia on spinal and supraspinal
levels.
 Local
anesthetic toxicity
 Bleeding/hematoma
 Infection
 Nerve injury
Transient paresthesias 1-3%
 Permanent nerve injury ~1/10,000

 Failed
block



Intravascular injection (immediate onset)
Systemic absorption (delayed onset)
Central nervous system signs
1st excitation: perioral tingling, tinnitus, agitation
2nd depression: blurred vision, slurred speech, loss
of consciousness
◦ Seizure
◦
◦

Cardiovascular toxicity
◦
◦
Cardiac arrhythmia and/or circulatory collapse
Requires ~ 3x blood concentration that causes
seizures
 For
use in the treatment of life
threatening local anesthetic
toxicity.
 Novel therapeutic indication for
an old medication (component of
TPN).
 First case reported in 2006, now
with over a dozen reported cases.
 Mechanism of action unknown
(“lipid sink?”).
 Needle
phobia or otherwise uncooperative.
 Excessive sedation (adults).
 Infection (local and untreated systemic).
 Anticoagulation?
 Pre-existing nerve injury.
 Surgery specific (e.g. motor block and postop neurological examination).
 Block specific (e.g. pulmonary disease and
interscalene block).
 Monitoring.
 Availability
of resuscitation equipment
(suction, airway management).
 Availability of resuscitation drugs (induction
agents, ACLS drugs, lipid emulsion).
 Pre-procedure confirmation (“timeout”).
 Aspiration before injection.
 Incremental injection.
 Do not inject when paresthesia present.
 Anatomy.
 Loss
of resistance and tactile feedback
 Evoked paresthesia.
 Nerve stimulator (goal 0.3-0.5 mA).
 Ultrasound guided.
PNS
Ultrasound
Children and adults who are already anesthetized
when a decision is made that regional block is an
appropriate technique.
 Individuals who are unable to report paresthesias
accurately.
 In performing local anesthetic administration on
specific nerve.
 In placement of stimulating catheters for anesthesia
or postoperative analgesia.
 Patients with chronic pain, in whom accurate needle
placement and reproduction of pain with electrical
stimulation or elimination of pain with accurate
administration of small volumes of local anesthetics
may improve diagnosis and treatment.


Motor fibers (Aα)require less
current than sensory element
(Aδ , C fibers).

Cathode(negative)electrode
should be attached to the
stimulating needle, not
anode(positive)electrode.

Current less than 0.5 mA is
essential to locate the nerve
successfully.
 Constant
current
output.
 The stimulating
pulse width should
be shorter(50100sec).
 A battery indicator
is essential.
 The polarity of the
leads should be
clearly marked.
Stimulating needle is connected to the
cathode.
 After the skin is disinfected, the needle is
advanced towards the nerve with the
stimulator at a relatively high current
intensity (1–2 mA) and with a pulse width of
100 to 200 μs.
 This higher current amplitude is necessary to
stimulate the nerve at some distance from
the needle.

The
current intensity decreased as
the needle approaches the nerve,
threshold current usually at 0.4–0.5
mA.
 Attempting to observe a twitch at
lower intensities (<0.3–0.4 mA) may
result in inadvertent intraneural
injection.
Once the acceptable threshold
current is reached, aspiration for
potential intravascular placement is
performed. With a negative
aspiration a test injection of local
anesthetic or normal saline (1–2 mL)
is performed. The muscle twitch
should diminish following the test
injection (Raj test).
The
mechanism of the Raj test
was previously thought to be
due to displacement of the
nerve by the injectate.
A recent interpretation of the
Raj test suggests that ionic
solutions influence the response
to nerve stimulation.
With pure sensory nerves, the
response will be a radiation of
paresthesia with each pulse
along the distribution of the
nerve. Additionally, the pulse
width used for nerve localization
should be somewhat higher (300
μs–1 ms).
 Sound
is mechanical vibration of particles in
a physical medium (air, blood, fat, etc).
 Sound comes in three "flavors": infrasound,
audible sound, and ultrasound, based on its
frequency
 There are 5 major steps that ultrasound
takes before an image can be made: sound
generation, transmission, reception or
reflection, reflection to transmission,
reception to processing image production
 8-12 MHz (multifrequency) linear probe (this
probe alone will suffice for 90% of practical
nerve blocks)
 Propagation
through dense objects e.g. bone is
poor with nearly the entire ultrasound beam
reflected (hyper echoic (bright) image ).
 Fat and tendon have low reflectivity thus they
form hypo echoic (dark) images.
 The outline of an object is generally best
delineated when the ultrasound beam is at 90
degrees.
 Generally speaking, nerves appear in the
transverse (cross sectional) view as round to
oval shaped structures that are nodular and
they can be hypo echoic or hyper echoic
depending on location. On the transverse view,
peripheral nerves in cross section often appear
to have an internal honey comb texture.



Ultrasound is generated when
multiple piezoelectric crystals
inside a transducer rapidly
vibrate in response to an
alternating current.
To generate a clinically useful
image, ultrasound waves must
reflect off tissues and return to
the transducer. The transducer,
after emitting the wave,
switches to a receive mode.
When ultrasound waves return
to the transducer, the
piezoelectric crystals will
vibrate once again, this time
transforming the sound energy
back into electrical energy.
•High frequency beam has a narrower beam width
•Resolution refers to the ability to clearly distinguish
two structures lying beside one another.
Low frequency = greater depth of
penetration but lower resolution
Anisotropy

Acoustic impedance =
resistance of a medium to the sound
transmission

Attenuation
loss of wave energy traveling through a
medium of different acoustic impedance

Cycle

Doppler effect
=
sound + movement -> modified frequency

Echogenicity
=
capacity of a structure in the path of an
ultrasound beam to reflect back sound waves

Frequency
=
=
the combination of one rarefaction and
one compression equals one cycle
= the number of cycles per unit time.
frequency is the reverse of wavelength.
The higher the frequency, the smaller the
wavelength.

Hyperechoic
=
an ultrasound image with echoes
stronger than normal or than surrounding
structures; images are bright on monitor;
examples are bone and pleura.

Hypoechoic
=
an ultrasound image with weaker echoes
than the surrounding structures; images
are dark on monitor; examples are
vessels and cyst.

Interface
=
boundary between two substances that
transmit sound at different velocities.

Velocity
=
speed at which sound waves travel
through a particular medium; velocity =
frequency x wavelength; ultrasound
velocity through human soft tissue = 1540
m/sec.

Wavelength
=
the distance between the onset of peak
compression or cycle to the next.
 Linear
 High
vs curved.
frequency vs low
frequency.
 “In-Plane”


Safer
Always see tip of needle
 Out-of-Plane”
May be easier.
 Risk losing sight of
needle tip.

 Superficial
nerves
need shallow settings.
 Deep
nerves need
deep settings.
 Resolution

Set by the transducer
frequency.
 Gain


Near
Far
 Color

doppler
Shows blood flow.
 Can
save to hard drive or disk.
 Able to print out hard copy.
 Able to save video.
 New reimbursement requirements
Must have proof that block was done with
ultrasound if you billed for it.
Regardless of the machine or transducer
selected, there are four basic transducer
manipulation techniques, which can be
described as the “PART” of scanning:
 Pressure (P): Various degrees of pressure are
applied to the transducer that are translated
onto the skin.
 Alignment(A): Sliding the transducer defines the
lengthwise course of the nerve and reference
structures.
 Rotation(R): The transducer is turned in either a
clockwise or counterclockwise direction to
optimize the image (either long or short-axis) of
the nerve and needle.
 Tilting(T): The transducer is tilted in both
directions to maximize the angle of incidence of
the ultrasound beam to the target nerve,
thereby maximizing reflection and optimizing
image quality.
Safety - no radiation.
 Visualize nerves.
 Visualize surrounding structures.
 Avoid complications.
 Visualize spread of local anesthetic.
 May be more reliable and quicker onset of
action.

 Visualize
 Advance
the internal anatomy.
the needle under real time guidance
(dynamic images).
 Observe the local injection (accuracy).
Any block technique works if you are good
 All current RCTs are small
 Ultrasound decreases::
 Onset time
 Number of needle passes
 Discomfort if stimulation is avoided
 Decreased LA volumes
 Increased successful rate

All about peripheral nerve block are true except:
a)
b)
c)
d)
More hemodynamic stability compared with neuroaxial
blocks.
Anticoagulation less of an issue.
Introduction of perineural catheters prolongs postoperative pain control benefits.
Postoperative nausea and vomiting are common.
All of the following are amide type local anesthetic
except:
a)
b)
c)
d)
Lidocaine.
Mepivacaine.
Prilocaine.
Cocaine.
One of the following drugs are used in the
treatment of local anesthetic toxicity:
a)
b)
c)
d)
Amiodarone
Digitalis
Atropine.
Intralipid infusion.
Current intensity that is necessary for successful nerve
block:
a)
b)
c)
d)
O.2mA.
0.3mA.
0.4mA
0.5mA.
All of the following are true except:
a)
b)
c)
d)
Ultrasound
Ultrasound
Ultrasound
Ultrasound
decreases
decreases
decreases
decreases
local anesthetic dose requirements.
discomfort if stimulation is avoided.
successful rate.
number of needle passes.