Peripheral Nerve Blocks





The editors and publisher would like to thank Dr. Adam B. Collins for contributing a chapter on this topic to the prior edition of this work. It has served as the foundation for the current chapter.


Introduction


The Role of Regional Anesthesia


Peripheral nerve blocks can provide surgical anesthesia and postoperative pain relief ( Table 18.1 ). Paresthetic techniques and peripheral nerve blocks have been used for decades. However, the main emphasis of this chapter will be on ultrasound guidance for peripheral nerve blocks. In addition, ultrasound guidance and nerve stimulation technologies can be combined for some regional blocks.



Table 18.1

Examples of Peripheral Nerve Blocks



















Origin Specific Block
Cervical plexus Superficial
Brachial plexus Interscalene
Supraclavicular
Infraclavicular
Axillary
Lumbar plexus Lateral femoral cutaneous a
Femoral
Adductor canal
Saphenous
Obturator a
Sacral plexus Proximal sciatic
Popliteal sciatic

a Not covered.



Preparation to Perform a Regional Nerve Block


Foundation of Knowledge


To perform safe and effective peripheral nerve blocks, an understanding of peripheral neuroanatomy, ultrasound technology, local anesthetic pharmacology, and risks associated with peripheral nerve blocks is needed.


Patient and Surgeon Factors


The willingness of the patient and the surgeon, as well as the anatomic location of the surgery, must be taken into consideration when incorporating peripheral nerve blocks into an anesthetic plan. A thorough preoperative review of the patient’s medical history, including any comorbid diseases, allergies, prior neuropathy, and concurrent anticoagulation medications, must be performed to rule out any contraindications in providing a peripheral nerve block.


Monitors and Equipment


Peripheral nerve blocks may be performed preoperatively in a dedicated block area or in the operating room. The patient must have a functional peripheral intravenous line, and monitoring equipment including pulse oximetry, electrocardiogram (ECG), and noninvasive blood pressure machine. Supplemental oxygen as well as emergency medications and airway equipment must be readily accessible. Sedation may be indicated, depending on the patient’s anxiety and magnitude of pain.


The patient, ultrasound machine, and anesthesia provider must be positioned in a way to optimize the nerve block being performed. For most blocks, the provider is positioned on the ipsilateral side and the ultrasound on the contralateral side of the block region. The choice of the ultrasound probe ( Fig. 18.1 ) and needle is dependent on the location of the peripheral nerve block as well, and the addition of placing a catheter will depend on the type of surgery being performed, the duration of hospital stay, and patient and surgeon preference.




Fig. 18.1


Ultrasound transducers for regional blocks.

From Gray AT. Atlas of Ultrasound-Guided Regional Anesthesia. 2nd ed. Philadelphia: Elsevier; 2013:22.


Choice of Local Anesthetic


The choice of local anesthetic for peripheral nerve blockade depends on a number of factors, including the desired onset, duration, and degree of conduction block (see Chapter 10 ). Lidocaine and mepivacaine, 1% to 1.5%, produce surgical anesthesia in 10 to 20 minutes that lasts 2 to 3 hours. Ropivacaine, 0.5%, and bupivacaine, 0.375% to 0.5%, have a slower onset and produce less motor blockade, but the effect lasts for at least 6 to 8 hours. The addition of epinephrine, 1:200,000 (5 μg/mL), can serve as a marker for intravascular injection and can increase the duration of a conduction block. In addition, through a decrease in the rate of systemic absorption, epinephrine can reduce peak plasma levels of local anesthetic. Considerations for the choice of local anesthetic solution for intravenous regional anesthesia are different from those for peripheral nerve blocks (see the later discussion under “Intravenous Regional Anesthesia [Bier Block]” ).


Regional Block Checklist


A standardized regional block checklist should be reviewed prior to performing a peripheral nerve block to improve safety. The checklist should include surgical consent and site marking, allergies and anticoagulation status, proposed peripheral nerve block and local anesthetic dose, side of the block, monitors implemented, emergency equipment available, and sedation plan.


Risks and Prevention


Infection


Infectious risk associated with a peripheral nerve block or placement of a peripheral nerve catheter is rare. However, an infection can cause significant morbidity and may lead to permanent neurologic injury. By performing proper hand hygiene, using maximal barriers during nerve block and catheter placement, and providing antiseptic solution at the site of insertion, the rate of infection can be reduced.


Hematoma


The risk of developing a hematoma depends on location of the peripheral nerve block being performed, the proximity to vascular structures, and vascular compressibility. With the use of ultrasound and proper aspiration technique, vascular puncture can be reduced. A review of the patient’s medical history with an emphasis on any anticoagulation medications is important. The American Society of Regional Anesthesia and Pain Medicine provides guidelines on anticoagulation management.


Local Anesthetic Systemic Toxicity (Also See Chapter 10 )


Local anesthetic systemic toxicity (LAST) secondary to local anesthetic absorption can range from mild symptoms to major neurologic and cardiovascular toxicity. A variety of factors including patient risk factors, concurrent medications, total local anesthetic dose, and anatomic location of the peripheral nerve block play a role in the risk of LAST. There is no single measure to prevent LAST; however, using the smallest effective dose, an incremental injection, aspiration prior to injection, an intravascular marker (i.e., epinephrine), and ultrasound guidance may decrease the risk of LAST. Lipid emulsion resuscitation remains the cornerstone of therapy to treat patients with LAST.


Nerve Injury


Nerve injury may result from direct needle trauma, inadvertent intraneural injection, or drug neurotoxicity. Serious neurologic injury from a peripheral nerve block is rare; however, the rate of transient paresthesia that resolves within days to weeks postoperatively is substantially higher. The use of ultrasound to identify nerves, limiting the injection pressure, and patient feedback may help decrease the rate of nerve injury, although clinical outcome data are limited.


Wrong-Sided Block


Wrong site, wrong procedure, and wrong patient peripheral nerve blocks are potentially serious medical errors that are inherent risks in performing any medical procedure. Although rare, this complication can be reduced by having a universal protocol that includes a checklist to ensure the correct patient, the proper surgery site, and correct laterality ( Table 18.2 ).



Table 18.2

Approximate Incidence of Adverse Events During Peripheral Nerve Blocks
















Adverse Event Approximate Incidence
Anesthetic systemic toxicity 1 in 1000
Peripheral nerve injury 1 in 1000
Wrong side/site block 1 in 10,000




Ultrasound Basics


An understanding of ultrasound imaging and transducer manipulation is important in providing safe and effective peripheral nerve blocks.


Basic Ultrasound Physics


Ultrasound imaging uses sound waves with frequency greater than 20 kHz. The use of ultrasound for medical purposes was first recognized in the 1930s. Since then, improvements in technology have paved the way to produce real-time images to help in diagnostics and interventions. Medical ultrasound machines use piezoelectric crystals in the transducer that convert electrical currents into mechanical pressure waves and vice versa, sending and receiving ultrasound echoes to thereby generate images.


As ultrasound waves pass through different body tissues the resistance to the propagation of ultrasound waves, or acoustic impedance, changes depending on the density of the tissue. Solid tissues have denser particles that effectively reflect waves that will be received by the transducer, displayed as brighter or hyperechoic structures. Less dense tissue does not reflect ultrasound waves as effectively, displayed as darker or hypoechoic structures. Tissues that do not reflect any ultrasound waves are considered anechoic.


Improving image resolution, or the ability to distinguish one structure from another, will optimize performance of peripheral nerve blocks. Increasing the frequency of the ultrasound wave will improve resolution of the image but will decrease the penetration of the ultrasound waves. Decreasing the frequency will lower the resolution but will improve the penetration to deeper tissue because there is less attenuation. Increasing the receiver gain (i.e., amplification of the returning echo signal) can to some extent compensate for attenuation.


Echogenic Properties of Nerves and Tissue


Peripheral nerves can be recognized on ultrasound scans by their fascicular echotexture. Central nerves (such as the cervical ventral rami) and very small nerves (such as the phrenic nerve) have a monofascicular or oligofascicular appearance ( Fig. 18.2 ). Most peripheral nerves have a polyfascicular appearance, which consists of a collection of small round hypoechoic dots (from the nerve fascicles or nerve fiber content) surrounded by hyperechoic stroma (from the nerve connective tissue). This pattern can be referred to as “honeycomb” or “bunch of grapes.” Although we use the term nerve fascicles , it is understood that only a subset of the total number of fascicles will be evident on an ultrasound scan because thin layers of connective tissue that divide fascicles cannot be resolved on the image. Nerves have a relatively constant cross-sectional area along their course, which helps distinguish these anatomic structures from tendons.




Fig. 18.2


This sonogram of the right side of the neck shows the roots of the brachial plexus as they pass between the anterior and middle scalene muscles. The core of these large peripheral nerves is less echogenic than the surrounding muscle. The phrenic nerve is a small hypoechoic structure seen on the anterior surface of the anterior scalene muscle. ASM, Anterior scalene muscle; MSM, middle scalene muscle; SCM, sternocleidomastoid muscle.


Ergonomics and Transducer Manipulation


Proper ergonomics are essential for ultrasound-guided interventions. It is important to maintain proper posture and position to reduce anesthesia provider fatigue (e.g., optimize patient position, bed height, and position of the display). A comfortable grip on the ultrasound transducer and resting the ulnar aspect of the transducer hand on the patient will promote stability. There are five basic transducer manipulation techniques to help optimize the ultrasound image: sliding, tilting, rocking, rotation, and compression. Peripheral nerves exhibit anisotropy, which means that the reflected echoes depend on the angle of insonation. The transducer can be tilted to maximize the returning echoes for the peripheral nerve. Slide and rotate the transducer to find the needle tip while maintaining nerve visibility. For some regional blocks the soft tissue will allow the transducer to rock back and reduce the angle of insonation, thereby improving needle tip visibility. Visual inspection is a good technique before using ultrasound guidance or if needle lineups are difficult. Most practitioners compress adjacent veins while introducing the needle to reduce the chance of venous puncture.


Regional Block Technique


There are multiple approaches to peripheral nerve blocks. Most blocks can be performed with a short-axis view of the nerve to be blocked. This view is stable for nerves with a relatively straight path. The in-plane technique, with the entire needle shaft and tip within the plane of imaging, is often used to guide needle placement ( Fig. 18.3 ). Alternatively, the out-of-plane approach can be used so that the needle tip crosses the plane of imaging as an echogenic dot. The quality of imaging and identification of structures is more important than approach. Differences in outcomes have been difficult to show when comparing various approaches to blocks in clinical studies.




Fig. 18.3


Approaches to regional block with ultrasound. LAX IP, Long-axis imaging, in-plane needle approach; LAX OOP, long-axis imaging, out-of-plane needle approach; SAX IP, short-axis imaging, in-plane needle approach; SAX OOP, short-axis imaging, out-of-plane needle approach.

From Gray AT. Atlas of Ultrasound-Guided Regional Anesthesia. 2nd ed. Philadelphia: Elsevier; 2013:32, Fig. 12-1.


Peripheral Nerve Catheters


Catheters can be placed adjacent to peripheral nerves for postoperative analgesia by infusion of dilute local anesthetic solutions. Continuous peripheral nerve blocks can be used in the hospital setting to facilitate vigorous early joint mobilization following orthopedic surgery. They can also be used to provide potent analgesia for outpatient surgery (also see Chapter 37 ). For placement of these catheters, the peripheral nerve should be first located in a fashion similar to that for single-injection blocks (typically ultrasound guidance with a large-bore needle), and then the catheter is threaded. Injection of a local anesthetic or dextrose solution immediately prior to catheter placement can be useful by creating more space adjacent to the nerve. Peripheral nerve catheters are more prone to dislodgment than epidural catheters because movement of skin near the catheter entry point is more likely.




Cervical Plexus Block


The cervical plexus is formed by the second, third, and fourth cervical nerves. With the patient’s head turned to the opposite side, the superficial cervical plexus can be blocked by infiltration of local anesthetic solution just deep to the platysma and investing fascia of the neck along the posterior lateral border of the sternocleidomastoid muscle ( Fig. 18.4 ). The anesthesia produced by a cervical plexus block includes the area from the inferior surface of the mandible to the level of the clavicle. A cervical plexus block is used most often to provide anesthesia in conscious patients undergoing carotid endarterectomy (see Chapter 25 ). Although combined superficial and deep cervical plexus blocks have traditionally been used for this surgical procedure, a superficial block alone is often sufficient.




Fig. 18.4


Anatomic landmarks and method of needle placement for a superficial cervical plexus block. With the patient’s head turned to the side, local anesthetic is infiltrated along the posterolateral border of the sternocleidomastoid muscle.

Modified from Brown DL, Factor DA, eds. Regional Anesthesia and Analgesia. Philadelphia: WB Saunders; 1996:245.




Upper Extremity Blocks


Brachial Plexus


The brachial plexus is a network of nerves that is composed of five nerve roots (C5, C6, C7, C8, and T1) that provide both motor control and sensory input for almost the entire upper extremity ( Fig. 18.5 ). The skin over the shoulder is supplied by the supraclavicular nerves of the cervical plexus, and the medial aspect of the arm is supplied by the intercostobrachial branch of the second intercostal nerve ( Fig. 18.6 ). The C5 to T1 nerve roots form ventral rami and trunks in the space between the anterior and middle scalene muscles in the cervical region and then pass over the first rib and under the clavicle. The trunks form three anterior and three posterior divisions, which recombine to create three cords in the infraclavicular region. These cords divide into terminal branches in the axillary region. The location of the surgery, experience of the anesthesia provider, and patient factors, such as body habitus, help determine where along the brachial plexus a peripheral nerve block should be performed ( Table 18.3 ).




Fig. 18.5


Roots, trunks, divisions, cords, and branches of the right brachial plexus.

Modified from Horlocker TT, Kopp SL, Wedel DJ. Nerve blocks. In Miller RD, ed. Miller’s Anesthesia. 8th ed. Philadelphia: Elsevier; 2015:1724, Fig. 57-3.



Fig. 18.6


(A) Cutaneous distribution of the cervical and thoracic roots of the upper extremity. (B) Cutaneous distribution of the peripheral nerves of the upper extremity.

Modified from Horlocker TT, Kopp SL, Wedel DJ. Nerve blocks. In Miller RD, ed. Miller’s Anesthesia. 8th ed. Philadelphia: Elsevier; 2015:1725, Fig. 57-4.


Table 18.3

Techniques for Brachial Plexus Block





























Technique Level Advantage Potential Drawback(s)
Interscalene Roots/trunks Shoulder coverage Hemidiaphragmatic paresis
Inferior trunk sparing
Supraclavicular Trunks/divisions Overall completeness Pneumothorax risk
Infraclavicular Cords Catheter placement Deep to pectoral muscles
Axillary Branches Shallow block Musculocutaneous nerve sparing

Only gold members can continue reading. Log In or Register to continue

Oct 21, 2019 | Posted by in ANESTHESIA | Comments Off on Peripheral Nerve Blocks
Premium Wordpress Themes by UFO Themes