When Should Nerve Blocks Be Used for Pain Management?

Introduction and Scope of the Problem

Pain is a frequent and feared symptom in patients with advanced illness. It is highly prevalent in cancer and many other advanced diseases, such as human immunodeficiency virus, multiple sclerosis, congestive heart failure, and renal failure. Most patients achieve satisfactory pain relief with the WHO Three-Step Analgesic Ladder, but 10% to 20% do not. With astounding advances in medical care, many patients are now living substantially longer but often with more complicated symptoms and expectations. Consequently, an extension of the ladder has been proposed to include interventional pain management and nerve blocks.

This chapter discusses diagnostic nerve blocks, which are used to establish a diagnosis or trial of treatment, and therapeutic nerve blocks, which are used to treat active pain. There are two types of therapeutic blocks: nonneurolytic nerve blocks, performed with a combination of local anesthetic and corticosteroid, and neurolytic nerve blocks, which utilize a nerve-killing agent such as phenol or ethyl alcohol.

Any nerve that can be reached by a needle is a candidate for a local nerve block. This includes not only the commonly known spinal nerve root injections and celiac plexus blocks, but also the less commonly used blocks such as brachial plexus and peroneal nerve blocks. Nerve blocks may be performed as one-time immediate injections or involve the placement of a small indwelling catheter connected to a slow infusion of local anesthetic for several days to “reset” neural pain pathways with prolonged pain relief.

The most important knowledge about nerve blocks for noninterventional pain professionals is the consideration of referring patients for these procedures early and knowing to whom to refer. Interventionalists spanning multiple specialties are often able to perform these procedures. Depending on the specific nerve block indicated, anesthesiology-trained or physiatry-trained pain specialists, interventional radiologists, and/or interventional gastroenterologists may be consulted to evaluate patients for such procedures. Given their effectiveness, nerve blocks should be considered common practice but are often withheld “until things get bad.” One of the most common responses in the authors’ experience after a patient has had a nerve block is “I wish I had done this months ago.”

Relevant Pathophysiology

Pain is a complicated phenomenon with multiple originating sites of pain impulses, propagation, reinforcement or inhibition, central nervous system and spinal cord “wind up,” and psychological responses. Nerve blocks, on the other hand, are local procedures designed to interrupt the pain impulse temporarily or permanently, allowing for the immediate relief of pain as well as remodeling the nerves involved and modulating their response to pain.

Several classes of medications are used in nerve blocks. The most frequently used are local anesthetics, which include drugs such as short-acting lidocaine and long-acting bupivacaine. Corticosteroids, such as methylprednisolone, triamcinolone, and dexamethasone, are administered in a local-release depot form and primarily have local reactions. Prolonged and frequent use can lead to systemic absorption and long-term side effects such as osteoporosis and cataracts, although these reactions are rare. Drugs with the most permanent effects are ethyl alcohol and phenol, which directly kill nerve fibers and the blood supply to local nerves. However, even with therapeutic neurolytic blocks, nerves will regenerate with time. The duration of pain relief of neurolytic blocks will vary between individuals, but in general, these blocks often must be repeated every 3 to 6 months.

Local nerve blocks have several mechanisms of action. The “unwinding” of a pain impulse is multifactorial, with components that include local pain impulse relief, relief of inflammation, reduction in propagation of the impulse, and remodeling of the nerve itself. Other mechanisms include disruption of vascular supply, alterations in gene expression and protein production, and modulations in secondary messengers. If interested, the reader may refer to other works that explore common mechanisms of pain relief.

Sympathetic nerve blocks target the sympathetic ganglia, which are located ventral and lateral to the spinal cord. These blocks are thought to work primarily by interrupting nociceptive afferent fibers from the areas involved with cancer, and/or decreasing visceral pain from thoracic, abdominal, or pelvic malignancies. Understanding anatomy and neurophysiology is critical to ensure that the ganglion to be blocked is separated anatomically from the somatic nerves and thus to minimize potential complications related to sensory and motor dysfunction, particularly in crucial areas such as the celiac plexus or the ganglion impar in front of the sacral-coccyx junction.

Techniques for Blocks

Contraindications for nerve blocks are similar to those for any other invasive procedure. Providers must always weigh the benefits of immediate and thorough pain relief against the risks of the procedure. A common contraindication is bleeding diathesis caused by anticoagulation or antiplatelet agents. The risk for bleeding is proportionally the same as with other procedures, but the adverse consequences of a large hemorrhage into the retroperitoneal space or a small hemorrhage near the spinal cord may be devastating. Another consideration is the risk of discontinuing a patient’s anticoagulation for the purpose of receiving a nerve block. Anticoagulants often need to be held prior to any invasive intervention, and nerve blocks are no exception. Many patients with advanced illnesses are on anticoagulation for prior pulmonary emboli or cardiac stents. The risk of discontinuing anticoagulation during the periprocedural period in high-risk patients may outweigh the benefit. Prior to proceeding with a nerve block, it is important to thoroughly discuss the risks and benefits with the patient as well as with other involved multidisciplinary providers.

Routine care before and after the block is similar to that in other procedures. Most centers require the patient to be observed for several hours afterward to ensure pain relief and absence of allergic reactions, hypotension, or significant diarrhea.

The first nerve blocks performed in the early 1900s, such as the celiac plexus block from the posterior approach, were done with knowledge of anatomy only. Modern practitioners typically use radiological tools to directly visualize the nerve or surrounding anatomy. Types of imaging used include fluoroscopy, computed tomography, magnetic resonance imaging, and/or ultrasonography. Furthermore, with the advent of safe and effective endoscopy, more blocks are being done through real-time endoscopic interventions. A comparison of the block types is presented in Table 14.1 .

Table 14.1

Approaches to Blocks

Approach	Advantages and Disadvantages
Anatomic	Universally available without equipment using traditional anatomic landmarks and elicitation of paresthesias.
Fluoroscopic guided	Requires inexpensive equipment; enables direct visualization of both anatomic landmarks and needle position.
Nerve stimulation guided	Nerve stimulator attached to 22-gauge needle is advanced to the area to be blocked. Motor nerves are stimulated first, causing a contraction visible to the operator, before any pain is felt. The nerve can then be blocked with local anesthetic. a If unsuccessful, subsequent attempts are challenging as the nerve will already be anesthetized, preventing twitches.
CAT (CT)-guided	Requires expensive equipment, but allows for direct visualization of anatomic landmarks, position of needle, and distribution of the anesthetic fluid.
Ultrasound guided	Localizes the exact area and surrounding blood vessels, allowing visualization of the block solution.
ERCP- or endoscopically- guided	Has the theoretical advantage of being concurrently diagnostic (brushing and biopsy) and therapeutic (stent placement or nerve block to control pain).

CAT , Computerized axial tomography; ERCP , endoscopic retrograde cholangiopancreatography.

a Franco CD, Vieira ZE. 1,001 subclavian perivascular brachial plexus blocks: success with a nerve stimulator. Reg Anesth Pain Med . 2000;25:41–46.

Ultrasound allows direct visualization of the nerve to give safer and more effective access to the region for the block. Previous studies demonstrate that ultrasound increases the likelihood and quality of a successful block and decreases time to onset of analgesia. Ultrasound is also particularly helpful when the anatomy has been changed by scarring, prior therapy, or metastases. Newer ultrasound capability also permits direct visualization of the nerve, blood vessels, and distribution of the injectate.

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