Introduction

The Peripheral Neuropathy Solution

Peripheral Neuropathy Program By Dr. Labrum

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Surgery of the upper and lower extremity presents anesthesiologists with an alternative to general anesthesia (GA), that being regional anesthesia (RA). RA is most often performed for postoperative analgesia, but RA may also be utilized as the primary technique for intraoperative anesthesia under certain circumstances and with certain patients. For years, neuraxial techniques (spinal or epidural) have been used as the sole regional anesthetic of choice for the lower limb. The advent of low molecular weight heparins (i.e., enoxaparin, fondaparinux) and the potential risk for the development of neuraxial hematomas have limited neuraxial technique use and have led to a much higher use of peripheral nerve blocks (PNBs) in everyday practice. Since the mid-2000s, great improvements have been made in equipment used to perform PNB, including stimulating peripheral nerve catheters and the use of ultrasound to guide in the placement of RA and to assist in the identity of nerves and nerve plexus (Marhofer et al. 2007).

Recent literature continues to show a growing body of evidence supporting the benefits of RA versus GA with respect to mortality, morbidity, postoperative analgesia, and functional recovery in certain surgical scenarios. Additional potential benefits of RA include increased operating room efficiency, improved pain control, and decreased incidence of chronic pain syndromes (Ballantyne et al. 1998, Beattie et al. 2001, Wu et al. 2004, Urwin et al. 2000). In one meta-analysis, Rodgers et al. (2000) showed a reduction in mortality of 33% with a significant decrease in the incidence of myocardial ischemic events, respiratory depression, rate of deep vein thrombosis (DVT) formation, and blood loss. Adequate pain management following surgery using a multimodal technique, including the use of cycloxygenase-2 inhibitors (COX-2 inhibitors), pregabalin or gabapentin, central neuraxial blockade, and PNB plays an important role in the management of acute postoperative pain and possibly the prevention of subsequent chronic pain syndromes (Reuben and Buvanendran 2007, Kehlet et al. 2006). Development of chronic pain syndromes following surgery shows some correlation to the severity of acute pain experienced during the immediate perioperative period (e.g., phantom limb syndrome).

However, the benefits of RA must be weighed against the possible negative aspects of RA that include consumption of operating room resources, potential patient discomfort, block failures, nerve injury, and toxic reactions to local anesthesia. Many of the negative aspects

N. Vadivelu et al. (eds.), Essentials of Pain Management,

DOI 10.1007/978-0-387-87579-8_21, © Springer Science+Business Media, LLC 2011

of RA stem from the fundamental fact that these procedures have traditionally been performed without the ability to visualize needle insertion, adjacent bloodvessels, and the spread of local anesthesia. In the past decade, there has been a valuable shift in the administration techniques of RA. Anesthesiologists can now visualize (in real time) neural anatomy, needle movement, collateral structures, and the perineural spread of local anesthesia. This is all possible secondary to the use of an "old" technology: ultrasound.

Described in this chapter are the commonly performed ultrasound-guided PNB that are used for some of the common upper and lower limb surgeries. The chapter will also include some of the new developments in this fast-growing area of RA and describe how to perform these blocks in every day practice. Basic principles for clinicians learning ultrasound-guided RA (USGRA) must be remembered and are keys to success in initial acquisition and refinement of skills for USGRA. A basic understanding of anatomy is required in order to utilize the ultrasound machine as a tool in the performance of RA. As Gaston Labat in 1928 stated, "Anatomy is the foundation on which the edifice of regional anesthesia is built." Some of the common tips or basic rules that serve as a guide for trainees are identified in Table 21.1.

Table 21.1 Basic guidelines for ultrasound-guided regional anesthesia (USGRA).

1. Proper ergonomics (position the patient, bed, and US machine to the proper height and position) will reduce operator fatigue

2. Know both applied and gross anatomy (use a nerve stimulator for confirmation when initially starting USGRA)

3. Optimize ultrasound image(s) of block area anatomy prior to PNB placement and identify footprint of US probe on patient's skin prior to proceeding

4. Recommended as a primary technique is to insert the PNB needle "in-plane" to the US probe

5. Visualize the PNB needle at all times and do not advance needle if needle tip cannot be visualized

6. Move head (eyes) or one hand at a time. Avoid movement of head or either hand simultaneously (helps to avoid a moving target and assists with orientation)

7. Stabilize the US hand and needle hand on the patient and grasp the US probe close to its base (extend the fingers of the US hand on the patient for added stability)

8. If needle visualization on US screen is lost, look at your hands, US probe, and the PNB needle (to confirm alignment) before repositioning

9. Follow nerve structure course (proximally and distally) a short distance, in order to confirm its identification as a nerve. Veins usually collapse and arteries do not when pressure is applied with the US probe

10. Visualize PNB needle tip and pertinent surrounding structures before LA injection. Surrounding tissues move upon LA injection (STOP if tissues do not move as PNB needle tip may be in a blood vessel). Be aware of proper injection pressure to avoid intraneural injections and aspirate frequently to assist in identifying intravascular injections

US, ultrasound; USRA, ultrasound-guided regional anesthesia; PNB, peripheral nerve block; LA, local anesthetic.

An understanding of nerve innervation of the surgical site is a prerequisite for a successful RA plan, and a grasp of perineural anatomy is needed to guide a needle to the site for local anesthetic injection with the least trauma and risk of complications from errant needle pass(es). Perineural anatomy and the ultrasound appearance of various tissue types are necessary to correctly locate local anesthetic injections for successful RA. With experience, ultrasound pattern recognition is developed and typical anatomy is rapidly identified. Anatomic expertise is fundamental to the development of ultrasound proficiency, but the regular use of ultrasound imaging teaches the practitioner a great deal about human anatomy and its variations.

The science of pain medicine has made great strides with regards to postoperative pain management, but many patients fail to receive these basic treatment protocols (Apfelbaum et al. 2003). Typically, physicians often base their perioperative pain management plan on the use of a single analgesic agent, usually an opioid. There is now abundant evidence that a multimodal approach to pain management is beneficial for patients (Kehlet and Dahl 2003, Kehlet and Wilmore 2002). The many benefits of multimodal analgesia are derived from the fact that using multiple agents blocks pain pathways at different sites and that the effects of these analgesic agents are not only additive but also often synergistic. This allows the use of lower doses of analgesics and thus reducing the dose-dependent side effects of any one single agent.

One aspect of multimodal analgesia protocols includes performance of PNB and, if possible, use of an indwelling nerve catheter (typically remains in place for 2-4 days postoperatively) to extend the beneficial effects of the nerve and nerve plexus blockade. Single-shot nerve blocks eventually wear off according to the pharmacokinetics and pharmacodynamics of the local anesthetic agents used (e.g., typically late at night following discharge from the one-day surgical center), and this can result in a period of severe pain because the patients may have no opioids within their system. The presence of an appropriately placed peripheral nerve block catheter(s) and a continuous infusion of local anesthetics may avoid this problem.

Deep vein thrombosis (DVT) poses a serious threat to patients undergoing general surgery and orthopedic procedures. A multitude of anticoagulant techniques and drugs are used, often dictated by the preference of the surgeon, with no uniform evidence-based criteria in which to optimize DVT prophylaxis. For use with a variety of anticoagulants in the presence of regional techniques, guidelines have been developed and presented by the American Society of Regional Anesthesia (ASRA) (Horlocker et al. 2003). These ASRA guidelines were intended for neuraxial techniques, but are often extrapolated to use with PNB. It is important to remember that these are guidelines and that when deciding whether to perform RA in the presence of potential coagulation issues, the clinician needs to balance the risk of a regional technique versus the risk imposed by GA. Based on the guidelines, a PNB should not be performed on a patient with suspected coagulation issues. As an example, a PNB should not be performed within 12 h of the last dose of low molecular weight heparin (LMWH) if a standard prophylactic dose (LMWH, 40 mg) has been used. With higher doses of LMWH, such as 1 mg/kg, waiting a period of 24 h should be necessary prior to nerve block placement. In the presence of LMWH, PNB catheters can be used, but should be removed 2 h prior to the next dose of LMWH administration. The ASRA guidelines for patients receiving platelet inhibitors suggest that clopidogrel should be stopped for 7 days prior to a major nerve block placement, whereas ticlopeidine would delay the placement of RA for 10 days. Other non-steroidal anti-inflammatory drugs (NSAIDs) and aspirin can be safely used in the presence of PNB.

Logistics and equipment needs for the performance and placement of regional anesthesia and PNB need to be considered. To perform these PNBs with a degree of efficiency and consideration of patient safety, it is important to have the appropriately developed protocols and readily available supplies and equipment. A preoperative block area with full monitoring and resuscitation equipment is one model that has been established. Complications associated with RA, some of them being life threatening, may follow the initiation of regional techniques, thus mandating the availability of resuscitative equipment. Recent studies indicate that 20% intralipid can be of benefit during resuscitation from negative cardiovascular events following the inadvertent intravascular injection of higher doses/concentrations of local anesthetics (especially bupivacaine) (Weinberg 2006a, b).

The presence of another assigned health-care provider (anesthesia attending, resident, Certified Registered Nurse Anesthetist (CRNA), or anesthesia assistant) in the preopera-tive block area can help with maintaining appropriate patient turnover and can also lead

Table 21.2 Drugs and equipment needed to perform regional anesthesia.

• Insulated stimulating needles (1, 2, 4, and 6 in.)

• Stimulating and nonstimulating PNB catheters

• Infusion pumps

• Ultrasound machine(s) with software specifically designed for regional anesthesia

• Sterile sheaths for ultrasound probes

• PNB stimulators

• Long-acting local anesthetics ropivacaine (0.5 or 0.75%) bupivacaine (0.5%) for postoperative analgesia ropivacaine (0.1 or 0.2%) bupivacaine (0.125 or 0.25%)

• short-acting local anesthetics mepivacaine (1.5%) lidocaine (2%)

for postoperative analgesia only mepivacaine (0.75%) lidocaine (1%)

epinephrine to make 1/400,000 solution

• Steri-strips, tincture of benzoin, and tagederm for securing PNB catheters

• Marker pens for identifying anatomical landmarks

• Resuscitative drugs midazolam for sedation and management of seizures

20% intralipid can be of benefit for the management of local anesthesia-induced arrhythmias thiopental for management of resistant seizures

• Resuscitative equipment oxygen ambubag and airway supplies endotracheal tube and laryngoscope equipment

PNB, peripheral nerve block.

to improved educational training and experience of assigned health-care providers (example: residents) (Martin et al. 2002). Table 21.2 represents the standard and minimum equipment, supplies, and drugs necessary when performing regional anesthesia.

Follow-up of patients with single-shot and PNB catheters is essential and necessary for the monitoring of efficacy, efficiency, and patient safety and satisfaction. The acute pain service (APS) or an anesthesiologist can readily assume this responsibility. The APS can also make important decisions about adjustment to infusion rates, the addition of adjuvants for pain management, and timing of PNB catheter(s) removal for patients admitted to the hospital (especially with reference to the administration ofanticoagulants).

Medicine is an ever-changing science and as new research and clinical experience broaden, that knowledge, changes in techniques and approaches are required. One of the most exciting advances in technology in relation to RA has been the introduction of anatomically based ultrasound imaging. Real-time viewing of the target nerve structures, the block needle trajectory, and local anesthetic spread, as well as critical structures to avoid, can better ensure success and safety in RA. USGRA is a quantum leap in technology; however, ultrasound visualization still generates indirect images which are subject to individual interpretation depending on one's experiences and training and where that training and experience were obtained. Additionally, it is important to obtain a good knowledge base of the physics on ultrasonography as well as to learn tools for avoiding imaging artifacts and other common mistakes. Literature on ultrasound imaging and guidance in RA is increasing, thus maintaining up-to-date versions of this information is necessary. Readers are advised to consult other sources of current literature related to the physics of ultrasonography and specific RA techniques used in clinical practice.

Basic ultrasound terminology is described in Table 21.3. Some basic clinical pearls for USGRA have been developed by utilization and application of the physics of the ultrasound machine(s). Structures of interest can be imaged either on the short axis (cross section) or on the long axis. A short-axis view becomes a long-axis view when the probe is turned 90° in either direction. In general, regional anesthesiologists prefer to image nerves and blood vessels on short axis because the operator has a simultaneous anterior-posterior and lateralmedial perspective. In the long-axis view, the lateral-medial perspective can be lost.

Two techniques are described in the literature with respect to needle insertion (Sites and Brull 2006). The needle can be inserted using an "in-plane" approach where the needle is inserted parallel to footprint of the ultrasound transducer such that it is visualized in long axis and allowing full needle visualization (Figs. 21.1a and 21.1b). Alternatively, the needle can be inserted perpendicular to the ultrasound transducer footprint, generating a short-axis view of the needle identified as "out-of-plane" (Figs. 21.2a and 21.2b). The major drawback

Table 21.3 Ultrasound terminology.

1. Ultrasound: sound waves that are at a frequency of 20,000 cycles/s or Hertz (Hz) or higher (most transducers used for UGRA are between 7 and 15 million Hz or 7-15 megahertz (MHz))

2. Ultrasound waves are produced when an electrical signal is placed across a piezoelectric crystal that forces the crystal to vibrate (vibration is then conducted through the body). Ultrasound waves are characterized by a specific wavelength and frequency Relationship between these variables:

c = (\)(f), where c = the propagation velocity (presumed to be 1540 m/s in the human body). Therefore, if c is held constant, then to increase the frequency of an ultrasound wave, the wavelength would have to proportionately decrease. (This concept is at the core of UGRA since different frequency probes are used for different blocks)

3. Ultrasound attenuation (a) and resolution (b): (a) Attenuation is the loss of ultrasound wave energy as it travels through tissue. Generally, a lower frequency wave will attenuate less at a given distance in comparison to a higher frequency wave. Thus, the lower frequency ultrasound wave will penetrate deeper into the patient and (b) axial resolution, or the ability to identify two or more points in space (one lying in front of the other), is between one and two wavelengths. This means that the lower frequency (larger wavelength) ultrasound beam will penetrate deeper but will lack the resolution of the higher frequency and smaller wavelength beam

4. Concepts of impedance (a) and reflection (b) form the "images" for UGRA. (a) Impedance can be referred to as the tendency of a medium to conduct ultrasound. When a sound wave travels through an object and contacts an adjacent object with different acoustic impedance, a demarcation is formed (e.g., would be nerve tissue surrounded by adipose tissue). (b) Reflection occurs at interfaces between objects with different acoustic impedances. The larger the difference in acoustic impedances, then the greater the reflection. Objects that are highly reflective are displayed as white or hyperechoic (fascial planes, bones, and some nerves). Objects that weakly reflect ultrasound waves are darker or hypoechoic (muscle, fat, and some nerves). Blood vessels are anechoic and appear black

5. Muscle is typically hypoechoic with internal striation, and the shape of various muscles and the characteristic appearance of fascial layers separating muscles produce specific pattern that becomes recognizable at each ultrasound site

6. Bone reflects ultrasound waves resulting in a bright, hyperechoic edge with shadowing (no image) deep to that edge

7. Veins and arteries are hypoechoic, round, or oval in short axis. Veins are readily collapsible with probe pressure and have respiratory variation in diameter while arteries are pulsatile; color-flow Doppler may be employed to help identify vascular structures

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Figure 21.1b Ultrasound image demonstrating anatomy of the axillary brachial plexus with needle approaching the brachial plexus in-line with the ultrasound probe.

to this out-of-plane approach is that a short-axis view of a block needle appears as a small hyperechoic dot on the screen that can sometimes be difficult to see. In addition, the operator is often then unable to confirm the exact location of the needle tip.

Ultrasound by the anesthesiologist is used for anatomical evaluation and to facilitate the performance of RA: both neuraxial and peripheral nerve blocks. Ultrasound technology is useful in patients with obscure anatomical landmarks, in patients with coagulopathy and neural pathology, and in patients suffering extremity trauma. Ultrasound provides an opportunity to visualize individual anatomical variations, and USGRA is typically performed by anesthesiologists and pain specialists in a procedure room or within the operating room. Table 21.4 identifies 10 steps of USGRA for improved RA success, efficacy, and patient

Figure 21.2a Photograph demonstrating probe placement and needle insertion point with needle position for an out-of-plane technique.

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Figure 21.2b Out-of-plane needle approach where needle tip (17G Tuohy) is visualized in transverse view and appears as a hyperechoic dot (arrow) on the ultrasound image. The target 'nerve' (N) is imaged in short axis.

safety. These fundamental steps should be followed during all RA procedures that utilize this technology.

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