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Nerve Blocks and Nerve Destruction


-- by David Leggett, M.D. and Clandis Andries Feler,M.D., F.A.C.S.

To a physician practicing pain management, the term nerve block is not very specifi. There are actually many different types of nerve blocks, each used for slightly different reasons. In the broadest sense, a nerve block simply means injecting a medication near a nerve that reduces or stops the ability of the nerve to transmit information to the brain.
Nerve blocks were first used for local or regional anesthesia before the tern of the twentieth century. These medications blocked nerve tissue from conducting messages back and forth, so that surgical procedures could be performed without requiring general anesthesia. The short that numbs your gums at the chemist's office is technically a nerve block. This type of nerve block has only a temporary effect, usually lasting a few hours at most.
Many years ago, anesthesiologists and other doctors began trying to treat various chronically painful conditions with nerve blocks. Obviously, the few hours of relief that were obtained with local anesthetics were not very beneficial to patients who hurt constantly, so the doctors began using other medications in addition to, or in place of, the local anesthetic. The Term nerve block continued to be used, however, even if no anesthetic was injected and the nerve signals never became blocked.
Today, a variety of very different procedures are all referred to as nerve blocks, Many difernet mecications can be injected including narcotics, steroids, antihypertension medications, anti-inflammatory medications, and others. Some of these medications are also used as intraspinal medications.
In addition to varying the medication injected, nerve blocks also very according to exactly where in the body the medications is placed. The location of the injection is generally divided into three categories: central, perrpheral, and sympathetic. Central blocks involve injections near the spine. Depending on the exact location of the injection, central blocks can also affect other structures such as bones, ligaments, intervertebral discs(the pad between each bone in the back), the joints of the back, and the spinal cord and spinal nerves. Peripheral nerve bocks involve injections near various nerves outside the spinal column. This could include nerves travelling to the legs, arms, face, or head. Sympathetic blocks involve injections of the sympathetic (unconscious) nerves.
1. Nerve BLocks for Spinal Pain
Cancer frequently causes back and spine pain both directly and indirectly. The most common direct cause of spine pain is the spread of the tumor to the vertibrae. Although any type of cancer can spread to the spine, certain types, such as breast, colon, and prostate cancers, are more likely to metastasize to the vertebrae. In a few instances, the sudden onset of back pain is the first indication that a patient has cancer.
Metastatic cancer causes pain by deforming the bone and stretching or irritating nerves in a tissue layer called the periosteum, whicha covers the bone. The cancer may also weaken a vertibra to the point that it collapses on itself, resulting in a compression fracture. In some cases, the cancer can invade or compress the spinal cord or its nerve roots, resulting in pain that mimics that of a ruptured disc.
Certain types of cancer can cause back pain without actually invading the spine. For exampl, abdominal tumor such as panscreatic cancer can invade tissues behind the abdomen. The distension and inflammation of the muscles and nerves compressed by the tumor result in pain inthe lower and middle back regions. Cancers of the kidney can cause similar effects.
The indirect effects of cancer probably cause as many cases of back pain in cancer patients as those caused by spread of the cancer to the spine. Cancer patients as those caused by spread of the cancer to the spine. Cancer patients often experience considerable fatigue both from the cancer and from treatments like radiation and chemotherapy. Patients are often forced to curtail physical activity and may become bedridden. This diminished physical activity increases the likelihood that muscle and connective tissue in and around the spinal column will become irritated and inflamed, resulting in substantial back or neck pain.
Spinal injections are a mainstay in the management of both back and neck pain caused by the direct and indirect effects of cancer. They can benefit patients suffering from spine pain caused by metastatic invasion of the spine, and those whose pain results from indirect effects such as muscle weakness.
2. Epidural Blocks
The most common nerve block performed the treatment of back or neck pain is undoubtedly the injection of cortisone into the epidural space of the spine, commonly called an epidural block. The epidural space is located within the bones of the spine, but outside the tough tissue covering the spinal cord, which is called the dura. "Epi" is the Latin root for outside, hence in an epidural block the medication into the spinal fluid that lies under the dura and is therefore referred to as a subdural injection.
Local anesthetic medication injected epidurally can provide anesthesia for surgery or labor pains and can control postoperative pain. The epidural injection of dilute local anesthetic solution containing cortisone (also called corticosteroids) can reduce nerve inflammation to improve chronic back or neck pain.
In the management of cancer-related pain, epidural injections can take two forms: a sigle injection or continuous infusion. The sigle or one-time injection is most common. A needle is placed in the proper location, and a quaintity of medication is injected followed by removal of the needle. The entire procedure takes only a few minutes.
The continuous infusion epidural is used only in certain specific conditions. A needle is inserted exactly as it would be for a ont-time injection. After needle placement, however, a very small catheter(medically, catheter means a soft tube) is threaded through the needle into the epidurai space. The needle is then withdrawn, but the catheter is left in the epidural space for anywhere from several days to several weeks, depending on the circumstances and method of insertion.
From a technical standpoint, epidural injections are relatively safe and painless. An intravenous infusion is started in all patients, both for safety and to administer sedation when needed. The amount of sedation varies according to the individual patient and the physician performing the procedure, but the goal is to provide patient comfort without creating complete unresponsiveness. This procedure is usually performed with the patient lying face down (prone), but in some cases the patient may remain sitting for the procesure.
In most pain treatment practices, the use of fluoroscopy (real-time X-ray) to confirm proper placement of the needle is routine; however, its use is not mandatory. The fluoroscope is used to show the relevant bony anatomy of the spine, and the insertion point is marked on the skin. The skin is then prepped with an iodine solution, and the insertion site is anesthetized with local anesthetic via a very small needle. The epidural needle is then inserted and directed to the proper location and depth using the X-ray for guidance. Once proper placement is achieved, the medication is injected (or the catheter inserted), the needle is removed, and the procedure is complete. The average epidural injection takes ten to twenty minutes to accomplish. Most patients can return home within an hour of completing the procedure.
Not all patients can undergo spinal injections, and some people require extra precautions before attempting the procedure. The two most common contraindications for spinal injection are infection and poor clotting of the blood. Infections anywhere in the body increase the possinility of the epicural needle becoming contaminated with bacteria, thus spreading the infection to the epidural space. Infection in the epidural space can cause meningitis or an epidural abscess. Since the epidural space is close to the spinal nerves and spinal cord, any infection in this area could have devastating consequences if not treated immediately. While the occurrence of an epidural abscess is very rare, the presence of an infection increases the risk enough so that the procedure should be delayed until the infection is fully treated.
Anticoagulation, the reduced ability of the blood to clot, can in rare cases lead to bleeding in the epidural space and the development of an epidural hematoma ( pool of blood in the tissue). The epidural space contains many small veins, and the needle sometimes punctures one of the veins during the procedure. In patients whose blood clots normally, the puncture heals naturally like any small wound. If the blood does not dot normally, the vein may continue to leak blood into the epidural space until a hematoma has formed. The hermatoma can exert pressure on the nerves and spinal cord, possibly causing permanent damage or requiring a major surgical procedure to relieve the pressure.
The other possible complications of epidural injection are all temporary. These include headache and backache. These complications are infrequent and almost always resolve within a day or two. A mild weakness or numbness is expected to occur from the local anesthetic, but will only last an hour or two, Overall, the risk of epidural injections is extremely low, and for most patients the potential benefits far outweigh the risks.
3. Other Blocks Near the Spine
There are several other injections used in the management of spine pain. There include spinal facet injections (injection into the joints between vetebrae), selective nerve root injections (injection into a single nerve as it leaves the spine), and intradiscal injections into the intervertebral discs). Each of these techniques can be helpful for treating certain specific causes of back pain, but none of them is particularly useful for treating cancer pain.
Intrathecal (also called subdural) injections are used to place medication into the spinal fluid. PLacing a needle into the subdural space to obtain a sample of spinal fluid for analysis is fairly common for paitents with certain types of cancer, but injecting medication into this space is done infrequently. Constant infusions of opiods (narcotics) into the spinal fluid is sometimes used for pain control>
Patients whose pain originates from pancreatic cancer may benefit from a special type of injection performed near the spine called a celiac plexus block. The celiac plexus is a collection of nerves that lies in front of the spine, near the aorta. This plexus transmits much of the pain information from the upper gastrointestinal system and the organs of the abdomen, including the pancreas.
Many patients with pancreatic cancer experience pain as their tumors invade the soft tissue structures near the pancreas. Blocking or deadening the celiac plexus may substantially reduce the pain. Patients who obtain good but shot-lived pain relief from a local anesthetic injection are often candidates for a longer lasting neurolytic (nerve destroying) injection.
A celiac plexus block can be performed by any of several techniques, but from the patient's standpoint the procedure is similar to that experienced during an epidural block. Most physicians perform the block using two needles, one advanced from each side of the back, instead of the single needle used for an epidural block. The needles also are placed deeper into the body than is needed for an epidural block. Foe this reason, patients usually are sedated rather heavily for a celiac plexus block. They are also likely to have muscle soreness in teir backs for several days after the procedure.
Patients who experience pain from pelvic or perineal (the floor of the pelvic) tumors may benefit from a superior hypogastric plexus block (to show you how silly medical terminology is, this literally translates as "upper lower stomach plexus"). This procedure is similar to a celiac plexus block, although it is performed in the lowest part of the back near the sacrum (tailbone). This injection may also be done using a neurolytic technique to provide long-lasting pain control, but this is not performed very often.
The complication rates for both the celiac plexus and superior hypogastric plexus blocks are somewhat higher than that of an epidural block. However, when performed with fluoroscopy (X-ray guidance), significant complications are very rare. Since the pain of pancreatic and pelvic cancers can be difficult to control with medication alone, the relief provided by these blocks can be particularly important.
Blocks for Peripheral Nerve Pain
Peripheral nerves are the major nerves that connect the spinal cord to various regions. Because the nerves follow well-mapped paths through out the body, it is possible to inject local anesthetics near the nerve at various locations, making a portion of the body insensitive. Many people have experienced peripheral nerve injections when a dentist numbs a tooth, or a physician sews up a small cut using local anesthesia.
Peripheral nerve injections are not used for the management of abdominal and lower extremity cancer pain very frequently, because elidural and subdural injections work so well for pain originating in these areas. However, peripheral nerve injections can be vitally important for managing cancer pain in the head and neck region. They are also used occasionally for pain originating from the chest wall and arms.
Cancers of the face, head, and neck can be extremely painful, since these areas have a very dense supply of nerves and are very sensitive to painful stimulation. Because the nerves of the head and face do not travel through the spinal cord (instead, these nerves pass directly though the the skull to the branstem), epidural and spinal block are of no benefit for pain above the neck. When pain medication cannot control the pain of head and neck cancer, injection of an anesthetic (sometimes with cortisone) near the nerves that are transmitting the pain can be very helpful.
A variety of different nerve blocks can be used in the head and neck region. The various indications for each block are somewhat technical, but generally they are classified as diagnostic, prognostic, or therapeutic. Diagnostic blocks use short-acting anesthetics (lidocaine is commonly used) to determine exactly which nerves are carrying the pain signals to the brain. In some cases, it is obvious which nerves are involved by the location of the pain, so a diagnostic block may not be needed.
Once the exact nerves involved have been determined, a prognostic block is performed to let the patient experience the potential consequences of a permanent neurolytic (nerve-destroying) injection. This block uses a longer acting local anesthetic that provides six to twenty-four hours of relief. It may seem silly to perform a prognostic block (many patients want to skip it and simply have the nerve destroyed permanently), but it is vitally important. Peripheral nerve blocks do not simply stop pain, they also result in areas of numbness and weakness within the distribution of that nerve (remember the effect some of those dental injections have on your lips). For some patients, a constant sensation of numbness can be more disabling than the pain that the injection is treating. Additionally, nerve blocks near the face many paralyze facial muscles, causing defficulties with chewing, swallowing, and speech. A prognostic block lets the patient determine how satisfied he might be with a permanent nerve block.
Therapeutic injections, cometimes called neurolytic blocks, involve injecting substances such as alcohol or phenol that chemically injure the nerve. A single neurolytic block can result in several months of pain relief. These nerve destruction procedures are discussed more thoroughly later.
Although head and neck pain is the the most common indication for peripheral nerve blocks, these procedures are sometimes used in other body regions. For example, patients