Peripheral Anesthesia

Question 1

Benefits of Peripheral Anesthesia

Answer 1

•Peripheral anesthesia provides potent analgesia and may decrease systemic analgesic requirements, opioid related side effects, general anesthesia requirements and the development of chronic pain

Question 2

Risks of Peripheral Anesthesia

Answer 2

Bleeding, infection, nerve injury, LAST

Question 3

Absolute and relative contraindications of peripheral anesthesia

Answer 3

Patient cooperation, bleeding disorders and anticoagulation, infection around needle insertion site, peripheral neuropathies

Question 4

Patients who might especially benefit from peripheral anesthesia include ___.

Answer 4

those with multiple comorbidities, benefit from opioid sparing technique (OSA, PONV) or with chronic pain

Question 5

Procedural Selection

Answer 5

• Understanding of regional anatomy and the surgical procedure are important when considering the appropriateness of a peripheral anesthetic.
• Surgical components, such as, tourniquet placement, bone grafting, projected surgical duration should be discussed with surgical colleagues.

Question 6

Field Block (general facts)

Answer 6

•A field block is a local anesthetic injection that targets terminal cutaneous nerves. (commonly used by surgeons to minimize pain)

Field blocks can also be used by CRNAs for superficial cervical plexus and intercostobrachial nerves

Question 7

Nerve Stimulation Technique

Answer 7

An insulated needle concentrates electrical current at the needle tip, while a wire attached to the needle hub connects to a nerve stimulator—a battery-powered machine that emits a small amount (0–5 mA) of electric current at a set frequency (usually 1 or 2 Hz)

When the insulated needle tip is placed in proximity to a motor nerve, specific muscle contractions are induced, and local anesthetic is injected

*can’t see how much you are injecting

Question 8

Ultrasound (mechanism of action)

Answer 8

• Ultrasound uses high-frequency (1–20 MHz) sound waves emitted from piezoelectric crystals that travel at different rates through tissues of different densities, returning a signal to the transducer.
• Depending on the amplitude of signal received, the crystals deform to create an electronic voltage that is converted into a two-dimensional grayscale image

Question 9

Echogenicity

Answer 9

–Hypoechoic: structures which sound pass easily and appear dark or black on the ultrasound screen. (air or fluid)

–Hyperechoic: structures reflecting more sound waves appear brighter or white on the ultrasound screen.

Question 10

The popliteal fossa contains __

Answer 10

• popliteal artery
• popliteal vein
• small saphenous vein
• tibial nerve
• common fibular nerve
• popliteal lymph nodes

Question 11

For ultrasound imaging, the anesthesia professional must select the transducer that ___.

Answer 11

strikes the optimal balance between the highest possible frequency and tissue penetration to the appropriate depth

Question 12

High-frequency transducers provide ___.

Answer 12

a high-resolution picture poor tissue penetration and are therefore used predominantly for more superficial structures

Question 13

Low-frequency transducers provide ____.

Answer 13

an image of poorer quality but have better tissue penetration and are therefore used for deeper structures.

Question 14

Linear probes ___.

Answer 14

do not distort images but curved probes may have benefits for deeper structures

Question 15

Which tenchique results in a smaller volume of local anesthetic?

Answer 15

Ultrasound technique usually results in a far smaller injected volume (10–30 mL) of local anesthetic as compared to nerve stimulation technique

Question 16

Axis and Plane

Answer 16

Needle insertion can pass either parallel (in-plane) or not parallel (out-of-plane) to the plane of the ultrasound waves

Nerves are best imaged in cross section, where they have a characteristic honeycomb appearance (short-axis)

Question 17

How do you confirm orientation of the ultrasound?

Answer 17

Confirm orientation of the probe relative to the image on the ultrasound screen

Every transducer has a fixed label on one end that corresponds to an adjustable label on the left or right side of the US screen

Question 18

Color Doppler

Answer 18

• Blood moving away from the transducer will return at a lower frequency than the original emitted wave and is represented by blue.
• Blood moving toward the transducer will return at a higher frequency than the original emitted wave and is represented by red.

Question 19

What happens when the depth is set too high?

Answer 19

decreases the size of the target structures displayed on the ultrasound screen

Question 20

What is a dropout?

Answer 20

Dropouts are an actual loss of image

They normally manifest as black lines running down the image.

You will want to determine if the issue is with the probe or the system. Try moving the probe cable and connector on the system to see if dropout moves/changes. Also try testing multiple probes on different ports and on another system. All of this will help determine if it is caused by the probe or the system.

Question 21

Equipment needed for a nerve block

Answer 21

• Needle Type
• Skin Prep
• Probe Cover

Question 22

Overall PEARLS of nerve blocks

Answer 22

1. Set up your machine properly.
2. Find the best ultrasound picture before inserting the needle into the skin.
3. Don’t advance the needle unless you see the needle.
4. Line up your needle axis to your probe axis.
5. Slide before tilt, and then before twist.
6. Keep needle perpendicular to the probe.
7. Rest your hand on the patient to stabilize.

Question 23

What areas are we targeting with an interscalene nerve block?

Answer 23

Roots C5–7 are most densely blocked with this approach; and the ulnar nerve originating from C8 and T1 may be spared

Question 24

Advantages of an interscalene nerve block

Answer 24

• Appropriate for shoulder and upper arm surgery.
• Risk of pneumothorax is small.
• Landmarks are easy to identify in obese patients.

Question 25

Disadvantages of an Interscalene block

Answer 25

* Paresthesias are elicited * Ulnar nerve is frequently not blocked

Question 26

Complications of an Interscalene block

Answer 26

* A properly performed interscalene block almost invariably **blocks the ipsilateral phrenic nerve** * The **hemidiaphragmatic paresis** may result in dyspnea, hypercapnia, and hypoxemia * A **Horner syndrome** (myosis, ptosis, and anhidrosis) frequently results from proximal tracking of local anesthetic and blockade of sympathetic fibers to the cervicothoracic ganglion * **Puncture of the vertebral artery** (1 mL of local anesthetic delivered into the vertebral artery may induce a seizure)

Question 27

Technique/Position for an Interscalene Block

Answer 27

* Patient is supine with neck turned away from side of block. * Sternocleidomastoid muscle is palpated. * Roll fingers off posteriorly. * Intersection at C6. _Needle insertion and injection_ * 23 gauge needle almost perpendicular to floor (45 degrees caudad, posterior, and medial). * Watch out for external jugular vein. * Injection performed (**20–40 ml**).

Question 28

Ultrasound technique for an interscalene block

Answer 28

* A high-frequency linear transducer is placed **perpendicular to the course of the interscalene muscles** * The brachial plexus and anterior and middle scalene muscles should be visualized in cross-section * The brachial plexus at this level **appears as three to five hypoechoic circles** * The carotid artery and internal jugular vein may be seen lying anterior to the anterior scalene muscle; the sternocleidomastoid is visible superficially as it tapers to form its lateral edge

Question 29

Supraclavicular Block

Answer 29

Supraclavicular block offers dense anesthesia of the brachial plexus for surgical procedures at or distal to the elbow

Question 30

Advantages of a Supraclavicular Block

Answer 30

* LA blockade can produce complete anesthesia for tissues between the mid-humerus and the fingers. * Brachial plexus is most compact here (3 divisions). * Small volume of solution is required * Quick onset. * Arm can be in any position. * Most homogeneous block of brachial plexus (ulnar nerve is anesthetized).

Question 31

Limitations of a Supracalvicular Block

Answer 31

Considerable experience required Pneumothorax is a risk

Question 32

Considerations of a Supraclavicular block

Answer 32

* Uncooperative patient. * Difficult stature. * Severe respiratory disease. * Bilateral upper extremity block * Avoid bilateral phrenic nerve block. * Avoid pneumothorax. * Inexperience.

Question 33

Ultrasound technique for a supraclavicular block

Answer 33

* The patient should lie supine with the head turned 30 degrees toward the contralateral side * A linear, high-frequency transducer is placed in the supraclavicular fossa superior to the clavicle and angled slightly toward the thorax * The subclavian artery should be easily identified. * The brachial plexus appears as multiple hypoechoic disks just superficial and lateral to the subclavian artery * The first rib should also be identified as a hyperechoic line just deep to the artery * Pleura may be identified adjacent to the rib and can be distinguished from bone by its movement with breathing

Question 34

Infraclavicular Block

Answer 34

Brachial plexus block at the **level of the cords** provides excellent anesthesia for procedures at or distal to the elbow

Question 35

Advantages of an Infraclavicular block

Answer 35

–Nerves frequently missed with the axillary approach are blocked. –BLOCKING BELOW THE LEVEL OF THE FIRST RIB WILL NOT ELIMINATE THE POTENTIAL FOR PNEUMOTHORAX . –The musculocutaneous nerve is blocked. –Unlike the axillary approach, does not require positioning of the arm.

Question 36

Limitations of an infraclavicular block

Answer 36

–No pulse to assist in locating bundle; needle must be advanced blindly. –If injection is too far proximal to the clavicle, the musculocutaneous and axillary nerves will be missed.

Question 37

Ultrasound technique for an infraclavicular block

Answer 37

* With the patient in the supine position, a small curvilinear transducer is placed in the parasagittal plane over the point 2 cm medial and 2 cm caudad to the coracoid process * The axillary artery and vein are identified in cross-section * The medial, lateral, and posterior cords appear as hyperechoic bundles positioned caudad, cephalad, and posterior to the artery, respectively * A long (10-cm) needle is inserted 2 to 3 cm cephalad to the transducer * Optimal needle positioning is between the axillary artery and the posterior cord, where a single **30-mL** injection is as effective as individual cord injections

Question 38

Axillary Nerve Block

Answer 38

* Performed at the level of the **terminal branches** * Plexus is located around the axillary artery . The location of the radial, median and ulnar nerves around the artery can be variable. Distinct branches are shallow, no where near the lung * Good choice for obese patients

Question 39

Ultrasound technique for an axillary nerve block

Answer 39

* Using a high-frequency linear array ultrasound transducer, the axillary artery and vein are visualized in cross-section * The pulsating axillary artery can be easily identified lying 1-3cm below the skin. * The brachial plexus can be identified surrounding the artery * The needle is inserted superior (lateral) to the transducer and advanced inferiorly (medially) toward the plexus under direct visualization. * Ten milliliters of local anesthetic is then injected around each nerve

Question 40

The axillary vein lies _____ to the artery.

Answer 40

caudad

Question 41

The radial, median and ulnar nerves can be identified as \_\_\_\_.

Answer 41

hyperechoic structures around the artery.

Question 42

The radial nerve is located \_\_\_\_.

Answer 42

deep/posterior to the axillary artery.

Question 43

The median nerve is \_\_\_.

Answer 43

superficial and cephalad to the artery.

Question 44

The ulnar nerve is \_\_\_\_.

Answer 44

caudad to the artery.

Question 45

The musculocutaneous nerve will often appear as a \_\_\_\_\_.

Answer 45

hypoechoic oval structure surrounded by a hyperechoic rim, located within the fascial plane between the bicep muscle and coracobrachialis

Question 46

Echogenicity of Veins

Answer 46

anechoic (compressible)

Question 47

Echogenicity of artieries

Answer 47

anechoic (pulsatile)

Question 48

Echogenicity of fat

Answer 48

hypoechoic with irregular hyperechoic lines

Question 49

Echogenicity of muscles

Answer 49

Heterogeneous (mixture of hyperechoic lines with hypoechoic tissue background)

Question 50

Echogenicity of Tendons

Answer 50

Predominantly hyperechoic

Question 51

Echogenicity of bones

Answer 51

hyperechoic lines with a hypoechoic shadow

Question 52

Echogenicity of nerves

Answer 52

hyperechoic

Question 53

If the gain is too high or too low what happens?

Answer 53

If gain is too high = image will look too hyperechoic If gain is too low = image will look too hypoechoic