Bm: Peripheral Nerve Blocks

Front 1

what things should be asked about before performing a peripheral nerve block on a patient?

Back 1

-examine the potential site of the block for signs of infection
-confirm normal coagulation status (ask about history of bleeding/bruising, or get coags if necessary)
-ask about preexisting neuropathy, especially in the area being blocked

Front 2

what is a good way to improve the acceptance of regional anesthesia by the surgeons?

Back 2

-doing the blocks in a block room to minimize delaying the operating rooms, and increase efficiency and turnover

Front 3

what things need to be in the block room?

Back 3

-appropriate monitors and equipment
-drugs in the event of an adverse reaction, or local anesthetic toxicity

Front 4

for similar reasons, what else must be present before doing a block?

Back 4

-an IV

Front 5

what factors influence the choice of local anesthetic for blocks?

Back 5

-desired onset
-duration
-degree of conduction block

Front 6

local that can be used for blocks

Back 6

includes:
-lidocaine
-mepivacaine
-ropivacaine
-bupivacaine

Front 7

lidocaine and mepivacaine used for blocks

Back 7

-solutions of 1-1.5% produce surgical anesthesia in 10-20 minutes, which lasts 2-3 hrs

Front 8

ropivacaine and bupivacaine

Back 8

-ropi 0.5% and bup 0.375%-0.5% have a slower onset and produce less motor block, but its effects last 6-8 hours

Front 9

adding epi

Back 9

-substantially increases the duration of the block
-decreases uptake, therefore decreasing the peak plasma concentration
-can also serve as a marked of intravascular injection

Front 10

what concentration of epi is used?

Back 10

1:200,000 (5 ug/ml)

Front 11

What methods can be used to locate peripheral nerves and guide the injection of local anesthetic?

Back 11

Include:
– paresthesias
– Nerve stimulation
– Ultrasound

Front 12

Paresthesias

Back 12

– Radiating electric shocklike sensations that can occur during regional anesthesia

Front 13

Historical use of paresthesias versus today

Back 13

– Historically the saying was "no paresthesias, no anesthesia," indicating they were necessary for successful block because the needle had to be in close proximity to the nerve
– Today, they may indicate the likelihood of nerve injury and therefore are not usually intentionally solicited

Front 14

What to do in the event of an elicited paresthesia?

Back 14

– Local anesthetic should not be injected because intramural injection is accompanied by intense pain and a high likelihood of permanent nerve injury
– The needle should be slightly repositioned before injection of local and static

Front 15

What is another common way of identifying peripheral nerves that carry a mixed population of sensory and motor fibers?

Back 15

– Nerve stimulation

Front 16

Anode and cathode during nerve stimulation

Back 16

– The block needle is used as the stimulating cathode in the lead somewhere on the body serves as the anode to complete the electrical circuit
– cathodal stimulation is more efficient than anodal stimulation so it is important not to reverse the leads during stimulation
– The location of the surface anode on the patient does not matter

Front 17

Currents used during nerve stimulation

Back 17

– A motor response evoked with currents of approximately 0.5 mA indicates sufficient location near the nerve for successful block
– Some have suggested a threshold stimulating current, the lowest current to produce a motor response, should be greater than 0.2 mA to ensure the tip of the needle is not intraneural

Front 18

What is the Raj test?

Back 18

– Injection of small amounts of local anesthetic, 1 – 2 mL, will Eliminate the motor response, probably by reducing current density near the tip of the needle rather than by physical separation of the needle in the nerve

Front 19

Concerns with nerve stimulation

Back 19

– Recent concerns have been raised that it may fail to elicit a motor response in some subjects

Front 20

When else might nerve stimulation fail to produce a response?

Back 20

– If the nerves of the plexus are not insufficient proximity to each other

Front 21

What should be done in this case?

Back 21

– Longer pulse widths, 0.3 ms rather than 0.1 ms, can be used to stimulate pure sensory nerves

Front 22

Can you use nerve stimulators which are meant to monitor neuromuscular blockade for peripheral nerve localization during blocks?

Back 22

– No they should not be used because they can deliver large currents, more than 50 mA, and may not accurately deliver the small currents used for peripheral nerve blocks, 0.4 - 2.0 mA

Front 23

What is another way to improve block success and minimize local anesthetic volume?

Back 23

Ultrasound

Front 24

What is a major advantage of ultrasound during blocks?

Back 24

– It allows you to appreciate variability in surface landmarks, body habitus, and patient positioning

Front 25

Example of using ultrasound to locate peripheral nerves

Back 25

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Front 26

What percentage of nerve fascicles can be seen with high-resolution ultrasound?

Back 26

One third

Front 27

How do peripheral nerves appear on the ultrasound?

Back 27

They have a fascicular architecture, a honeycomb appearance

Front 28

What ultrasound frequencies are required to distinguish tendons from nerves on ultrasound?

Back 28

10 MHz

Front 29

High - frequency ultrasound

Back 29

Provides better resolution but poor penetration into deeper tissue because of attenuation of the sound beam

Front 30

What does visibility of the needle during a block depend on?

Back 30

The gauge and insertion angle

Front 31

Why are peripherral nerve catheters more likely to dislodge than epidural catheters?

Back 31

Because of greater skin movement near the catheter entry point

Front 32

What forms the cervical plexus?

Back 32

-the first 4 cervical nerves

Front 33

superficial cervical plexus block

Back 33

-turn the patients head to the opposite side, then infiltrate local just deep to the platysma and investing fascia, along the posterior lateral border of the SCM

Front 34

area blocked by the superficial cervical plexus block

Back 34

-from the inferior surface of the mandible to the level of the clavicle

Front 35

picture of superficial cervical plexus block

Back 35

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Front 36

for what is the superficial cervical plexus block most often used, and what other technique was used but isnt anymore, and why?

Back 36

-most often to do awake CEAs
-used to combine this with a deep cervical plexus block, but studies have shown the deep isnt necessary

Front 37

from where does the brachial plexus arise?

Back 37

-from the anterior rami of C5-T1

Front 38

brachial plexus anatomy

Back 38

-the anterior rami of C5-T1 unite to form 3 trunks in the space between the anterior and middle scalene muscle, then pass over the first rib and under the clavicle to enter the axilla; the trunks then form 3 anterior and posterior divisions, which recombine to form 3 cords, which then divide into terminal branches which supply all of the motor and sensory innervation to the upper extremity, with a couple exceptions

Front 39

exceptions

Back 39

-the skin over the shoulders is supplied by the cervical plexuses
-the medial aspect of the arm is supplied by the intercostalbrachial branch of the 2nd intercostal nerve

Front 40

picture of cutaneous innervation of the upper extremity

Back 40

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Front 41

anesthetizing the brachial plexus

Back 41

-can be done anywhere along its course, but is most commonly done in 4 places:

1. interscalene
2. supraclavicular
3. infraclavicular
4. axillary

Front 42

at what level does an interscalene block anesthetize the brachial plexus?

Back 42

-roots/trunks

Front 43

whats the potential drawback of the interscalene?

Back 43

it spares the inferior trunk

Front 44

how to do an interscalene block

Back 44

-25 to 40 ml
-the interscalene groove is adjecent to the transverse process of C6, with the external jugular vein often overlying the area, and the brachial plexus will be superficial, 1-2 cm below the skin

Front 45

picture of interscalene

Back 45

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Front 46

does a paresthesia of the shoulder reflect stimulation of the brachial plexus?

Back 46

-it may not, but it is associated with anesthesia sufficient for shoulder surgery

Front 47

so with injection of 40 ml of local, what is anesthetized and what is not?

Back 47

-the cervical and brachial plexuses will be anesthetized (thus permitting surgery of the AC joint)
-the ulnar side of the forearm and hand (C8-T1, inferior trunk) will be spared)

Front 48

risks with interscalene block

Back 48

-pneumothorax
-phrenic nerve block
-recurrent laryngeal nerve block
-epidural or spinal injection
-injection into the vertebral artery

Front 49

pneumothorax and interscalene

Back 49

-the risk is remote, but consider the diagnosis if cough or chest pain is produced during the block

Front 50

phrenic nerve block and interscalene

Back 50

-the phrenic nerve lies on the anterior scalene muscle, so block of the ipsilateral phrenic nerve is expected with resultant hemidiaphragmatic paralysis
-normal pts will be asymptomatic, but pts with respiratory insufficiency or contralateral phrenic nerve palsy will poorly tolerate the condition

Front 51

recurrent laryngeal nerve block and interscalene

Back 51

-occurs less commonly than phrenic nerve block, but could cause complete airway obstruction in patients with contralateral vocal cord palsy
-be careful in pts with a preop history of hoarseness or neck surgery

Front 52

how can you reduce the chance of an epidural, subarachnoid, or vertebral artery injection of local?

Back 52

-angle the needle caudad so it is more likely to contact an adjacent transverse process than pass between them

Front 53

what will happen if local is injected into the vertebral artery?

Back 53

-immediate seizures, so use meticulous aspiration

Front 54

What level is blocked with a supraclavicular block?

Back 54

– Trunks/divisions

Front 55

What is the potential drawback of a supraclavicular block?

Back 55

– Risk for pneumothorax

Front 56

Supraclavicular block

Back 56

– Achieved by injecting 25 to 40 mL of local anesthetic

Front 57

Complications of supraclavicular block

Back 57

– The most common is pneumothorax (about 1% incidence)
– Phrenic nerve block occurs frequently (50%)

Front 58

Signs of pneumothorax after supraclavicular block

Back 58

– Cough, dyspnea, or pleuritic chest pain

Front 59

Significance of phrenic nerve block during supraclavicular block

Back 59

– Usually insignificant, however bilateral supraclavicular blocks are not recommended for fear of bilateral phrenic nerve paralysis, Likewise patients with COPD may not be good candidates for supraclavicular block

Front 60

What are the advantages of the supraclavicular block?

Back 60

– Rapid onset and ability to perform the block with the arm in any position

Front 61

What may limit the use of this block in outpatients?

Back 61

The risk of pneumothorax

Front 62

What level is being blocked with an infraclavicular block?

Back 62

Cords

Front 63

What is the potential drawback of an infraclavicular block?

Back 63

Pectoral discomfort

Front 64

What procedures is an infraclavicular block good for?

Back 64

– Procedures of the hand, forearm, and elbow

Front 65

Infraclavicular block

Back 65

– The cords are blocked in the axilla, just distal to the clavicle
– The needle path is far from the lung and neuraxis, and the block occurs where the cords of the brachial plexus are tightly surrounding the axillary artery

Front 66

Landmark technique for infraclavicular block

Back 66

– With the arm abducted to 90°, a line is drawn between the ipsilateral C6 transverse process and the pulsation of the axillary artery, A mark is then made 2.5 cm distal to the location where the line crosses the clavicle, and a needle is advanced toward the underlying course of the axillary artery until paresthesias or nerve stimulation is achieved, then 30 to 40 mL of local anesthetic injected

Front 67

Nerve stimulation forced infraclavicular block

Back 67

– an evoked motor response below the elbow is consistent with favorable spread suggesting that one of the three chords has been identified rather than a nerve branch which may have already left the fascicle

Front 68

Surface anatomy for infraclavicular block

Back 68

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Front 69

Picture of infraclavicular block technique

Back 69

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Front 70

Disadvantages of infraclavicular block

Back 70

– Vascular injection
– Patient discomfort

Front 71

Level of block for axillary block

Back 71

Branches

Front 72

Potential drawback of axillary block

Back 72

-spares the musculocutaneous nerve

Front 73

What procedures can the axillary block be used for?

Back 73

– Procedures of the hand forearm and elbow

Front 74

Brachial plexus within the axilla

Back 74

– The terminal branches of the brachial plexus reside within the axillary sheath and in the tissue that immediately surrounds it

Front 75

Ultrasound view of axillary block

Back 75

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Front 76

Picture of axillary block

Back 76

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Front 77

Transarterial approach to axillary block

Back 77

-the patient is supine with the arm abducted to 90; the needle is inserted through the artery until no more blood is aspirated, the needle should now be in the potential space of the axillary sheath, half the volume is injected here, the needle is then withdrawn and once out the other side of the artery the other half is injected
-an additional 5ml is injected in a fanning pattern in the coracobrachialis to block the musculocutaneous nerve, and another 5ml into the subQ tissue superficial to the artery to block the intercostobrachial, medial brachial cutaneous, and medial antebrachial cutaneous nerves

Front 78

Advantages of axillary block

Back 78

– Remote from the lung and neuraxis therefore safe

Front 79

Potential complications of axillary block

Back 79

– Systemic local anesthetic toxicity
– Nerve injury from needle trauma, intraneural injection, or hematoma