Peripheral Anesthesia Flashcards
Benefits of Peripheral Anesthesia
•Peripheral anesthesia provides potent analgesia and may decrease systemic analgesic requirements, opioid related side effects, general anesthesia requirements and the development of chronic pain
Risks of Peripheral Anesthesia
Bleeding, infection, nerve injury, LAST
Absolute and relative contraindications of peripheral anesthesia
Patient cooperation, bleeding disorders and anticoagulation, infection around needle insertion site, peripheral neuropathies
Patients who might especially benefit from peripheral anesthesia include ___.
those with multiple comorbidities, benefit from opioid sparing technique (OSA, PONV) or with chronic pain
Procedural Selection
- 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.
Field Block (general facts)
•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
Nerve Stimulation Technique
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
Ultrasound (mechanism of action)
- 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
Echogenicity
–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.
The popliteal fossa contains __
- popliteal artery
- popliteal vein
- small saphenous vein
- tibial nerve
- common fibular nerve
- popliteal lymph nodes
For ultrasound imaging, the anesthesia professional must select the transducer that ___.
strikes the optimal balance between the highest possible frequency and tissue penetration to the appropriate depth
High-frequency transducers provide ___.
a high-resolution picture poor tissue penetration and are therefore used predominantly for more superficial structures
Low-frequency transducers provide ____.
an image of poorer quality but have better tissue penetration and are therefore used for deeper structures.
Linear probes ___.
do not distort images but curved probes may have benefits for deeper structures
Which tenchique results in a smaller volume of local anesthetic?
Ultrasound technique usually results in a far smaller injected volume (10–30 mL) of local anesthetic as compared to nerve stimulation technique
Axis and Plane
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)
How do you confirm orientation of the ultrasound?
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
Color Doppler
- 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.
What happens when the depth is set too high?
decreases the size of the target structures displayed on the ultrasound screen
What is a dropout?
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.
Equipment needed for a nerve block
- Needle Type
- Skin Prep
- Probe Cover
Overall PEARLS of nerve blocks
- Set up your machine properly.
- Find the best ultrasound picture before inserting the needle into the skin.
- Don’t advance the needle unless you see the needle.
- Line up your needle axis to your probe axis.
- Slide before tilt, and then before twist.
- Keep needle perpendicular to the probe.
- Rest your hand on the patient to stabilize.
What areas are we targeting with an interscalene nerve block?
Roots C5–7 are most densely blocked with this approach; and the ulnar nerve originating from C8 and T1 may be spared
Advantages of an interscalene nerve block
- Appropriate for shoulder and upper arm surgery.
- Risk of pneumothorax is small.
- Landmarks are easy to identify in obese patients.
Disadvantages of an Interscalene block
- Paresthesias are elicited
- Ulnar nerve is frequently not blocked
Complications of an Interscalene block
- 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)
Technique/Position for an Interscalene Block
- 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).
Ultrasound technique for an interscalene block
- 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
Supraclavicular Block
Supraclavicular block offers dense anesthesia of the brachial plexus for surgical procedures at or distal to the elbow
Advantages of a Supraclavicular Block
- 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).
Limitations of a Supracalvicular Block
Considerable experience required
Pneumothorax is a risk
Considerations of a Supraclavicular block
- Uncooperative patient.
- Difficult stature.
- Severe respiratory disease.
- Bilateral upper extremity block
- Avoid bilateral phrenic nerve block.
- Avoid pneumothorax.
- Inexperience.
Ultrasound technique for a supraclavicular block
- 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
Infraclavicular Block
Brachial plexus block at the level of the cords provides excellent anesthesia for procedures at or distal to the elbow
Advantages of an Infraclavicular block
–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.
Limitations of an infraclavicular block
–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.
Ultrasound technique for an infraclavicular block
- 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
Axillary Nerve Block
- 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
Ultrasound technique for an axillary nerve block
- 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
The axillary vein lies _____ to the artery.
caudad
The radial, median and ulnar nerves can be identified as ____.
hyperechoic structures around the artery.
The radial nerve is located ____.
deep/posterior to the axillary artery.
The median nerve is ___.
superficial and cephalad to the artery.
The ulnar nerve is ____.
caudad to the artery.
The musculocutaneous nerve will often appear as a _____.
hypoechoic oval structure surrounded by a hyperechoic rim, located within the fascial plane between the bicep muscle and coracobrachialis
Echogenicity of Veins
anechoic (compressible)
Echogenicity of artieries
anechoic (pulsatile)
Echogenicity of fat
hypoechoic with irregular hyperechoic lines
Echogenicity of muscles
Heterogeneous (mixture of hyperechoic lines with hypoechoic tissue background)
Echogenicity of Tendons
Predominantly hyperechoic
Echogenicity of bones
hyperechoic lines with a hypoechoic shadow
Echogenicity of nerves
hyperechoic
If the gain is too high or too low what happens?
If gain is too high = image will look too hyperechoic
If gain is too low = image will look too hypoechoic
