John M Mathis

The Peripheral Neuropathy Solution

Neuropathy Solution Program

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Imaging Equipment

Most image-guided spine interventions are accomplished well with fluoroscopic guidance. It goes without saying that good visualization of the anatomical area being treated is necessary. Most modern fluoro-scopic equipment will provide this capability. It is important to view the target anatomy from multiple projections, and therefore a C-arm configuration is need. Fixed-plane fluoroscopic equipment (commonly used for gastrointestinal work) is not sufficient. The most sophisticated equipment in the multidirectional category is the fixed-base, biplane fluoroscopic room (Figure 2.1A). These rooms are common for inter-ventional neuroradiologists but are not routinely available otherwise. The ability to view the target anatomy in two projections at once is a definite luxury and offers the fastest possible needle insertion capability. However, single-plane C-arm systems are fine for all these procedures. The greatest disadvantage is the reduced speed experienced with vertebroplasty and kyphoplasty, but these procedures can also be performed adequately without biplane capability. Fixed-base C-arm (dedicated angiographic) rooms (Figure 2.1B) are more desirable than portable C-arms (Figure 2.1C). This is primarily because of image quality but also because of the ease of use by the operating physician. Fixed-base angiographic equipment is motorized and can be controlled by the physician. By contrast, in most portable units projection changes must be made manually by a technologist. This requirement has the disadvantage of requiring the physician to describe the desired projection rather than being able to select it personally and generally slows the process. Also, projections that are repeatedly used can be programmed into memory on a fixed-base machine and automatically retrieved with the press of a button. These features make the use of the fixed-base rooms simpler and faster.

Fixed Base Operators
Figure 2.1.
Neuropathy Clinic Arm Unit

Figure 2.1. (A) Biplane fluoroscopic equipment is the most sophisticated and useful of the possible room setups. However, it is extremely expensive and not generally available for the average spine imaging operator. (B) A fixed, single-plane fluoroscopic arrangement that affords a fluoroscopic image of excellent quality. The C-arm is motor driven and computer controlled for ease of operation. It will be slower than the maximally efficient biplane room seen in (A). (C) A modern, mobile C-arm fluoro-scopic arrangement commonly used in operating room situations. This apparatus offers good imaging capability but is much more cumbersome to use than the fixed-base systems. Though acceptable, it is the least desirable setup.

Figure 2.1. (A) Biplane fluoroscopic equipment is the most sophisticated and useful of the possible room setups. However, it is extremely expensive and not generally available for the average spine imaging operator. (B) A fixed, single-plane fluoroscopic arrangement that affords a fluoroscopic image of excellent quality. The C-arm is motor driven and computer controlled for ease of operation. It will be slower than the maximally efficient biplane room seen in (A). (C) A modern, mobile C-arm fluoro-scopic arrangement commonly used in operating room situations. This apparatus offers good imaging capability but is much more cumbersome to use than the fixed-base systems. Though acceptable, it is the least desirable setup.

New fluoroscopic equipment generally has good image quality. This may not be true of older equipment; therefore old equipment should be checked by a certified radiological physicist for image quality and radiographic exposure or output. Additionally, portable equipment may not have enough power to penetrate thick body areas. This can limit visualization in some situations and reduce the safety of procedures. Ultimately, all fluoroscopic images face this limit. Large patients or difficult locations, such as the high thoracic region (lateral T1-T4, which are blocked by the shoulders), will have limited visualization. In these situations, alternate imaging should be considered.

The use of computed tomography (CT) has grown both because of its availability and because of the limitations of fluoroscopy. Some operators use CT simply because it is what they have available. Certain regions of the body that may be hard to image with fluoroscopy are better suited to CT imaging. Additionally, complex clinical situations, such as percutaneous vertebroplasty, used to treat neoplastic destruc tion of the posterior wall of vertebra, may be aided by CT imaging. While CT offers some potential advantages for a limited number of situations, it is generally less available, more expensive, and slower than fluoroscopic imaging. Finally, the user of CT relinquishes the capability for real-time visualization of contrast or cement injection. These restrictions keep the use of CT limited to a small number of cases and situations.

Pharmacological Agents for Spine Intervention

Corticosteroids

Corticosteroids have a long history in the treatment of pain related to spine disease and have been used since the 1960s. At that time, they were injected both epidurally and intrathecally for pain management. By the 1980s there were reports of complications that included arachnoiditis, meningitis, and paraparesis/paraplegia.1,2 Controversy was sufficient in Australia to prompt explicit government warnings about the use of corticosteroids for epidural pain management.3 Review of the scientific literature regarding these findings suggests that many of the complications resulted from or were associated with the intrathe-cal use of corticosteroids.1-5 We know that some definite side effects can result from these drugs; physicians should be aware of these and should discuss potential complications with their patients.

When used in spine injections, corticosteroids are believed to help produce chemical stabilization of the local environment. This is accomplished by reducing the local amount of phospholipase A2 and arachidonic acid, as well as by decreasing the cell-mediated inflammatory and immunological responses.

The most common corticosteroid used for spine injections has been a long-acting form of methylprednisolone acetate (Depo-Medrol; Pharmacia-Upjohn). This material is available in doses of both 40 and 80 mg/mL. The acetate formulation is quite insoluable in water and has a long half-life in tissues. Its relative strength is approximately five times that of hydrocortisone. It often contains the preservative polyethylene glycol, which is thought to be potentially neurotoxic. Indeed, this material may be the source of arachnoiditis created with intrathe-cal injection of Depo-Medrol. Depo-Medrol is particulate and therefore can cause stroke if injected intra-arterially (i.e., into the vertebral artery during an attempted cervical foraminal injection). Adding anesthetic solutions exacerbates the problem because the combination increases precipitation within the syringe.

A more recent option for an injectable corticosteroid is the combination of betamethasone sodium phosphate and betamethasone acetate (Celestone Soluspan; Schering). This mixes a short- and a long-acting form of betamethasone in the same injectable solution. It contains no preservative and comes in doses of 6 mg/mL. Betamethasone is approximately 30 times as strong as hydrocortisone. It seems to have a less particulate nature and a decreased tendency to precipitate when mixed with anesthetics. All these properties make it less apt to create arachnoiditis when injected intrathecally and less prone to create stroke if given intra-arterially. Recently both Depo-Medrol and Celestone have gone through periods of decreased availability. This has caused some labs to use a long-acting form of triamcinolone (Aristocort; Fuji-sawa USA).6 This material is particulate (similar to Depo-Medrol) and also contains the preservative polyethylene glycol. It is available in doses of 25 mg/mL and is approximately five times as strong as hydrocortisone. It seems to offer no advantage over Depo-Medrol.

Anesthetic Agents

Local anesthetic agents are commonly added as part of the injectate used for numerous spinal and pain management injection procedures. Local anesthetics block the sodium channel, completely halting electrical impulse conduction in peripheral nerves, spinal roots, and autonomic ganglia.7 To block nerve conduction, the local anesthetic must cover at least three consecutive sodium channels (nodes of Ranvier). Differential blocking occurs because fibers carrying different types of information (pain, sensory, motor) are of different size. The smallest of these are the nociceptive (pain) fibers. These fibers attain calcium channel blockade with the smallest amount of anesthetic. Progressively larger fibers require a larger volume of anesthetic to block enough adjacent channels to stop conduction. Pain fibers are the most sensitive, followed by sensory, and finally motor fibers. This differential blocking allows pain relief without obligatory motor blockade.

Local anesthetics are organic amines with an intermediary ester or amide linkage separating the lipophilic ringed head from the hy-drophilic hydrocarbon tail. The amino ester group of anesthetics includes procaine, tetracaine, and benzocaine. These anesthetics have been used for a long time and are known to have a higher allergic potential than the amide-linked group of anesthetics (lidocaine, bupiva-caine, and ropivacaine) now in common usage. The amino ester group is thought to have their allergic potential because of their metabolite p-aminobenzoic acid (PABA). The members of the amide group, which do not have this metabolite, are known to have a very low allergic potential and little cross-reactivity. However, the amide group may contain the preservative methylparaben, which is metabolized to PABA and can produce cross-reactivity for potential allergic reactions with the ester group. Preservative-free amide anesthetics are therefore recommended for all injection procedures.

Lidocaine is a common first-generation member of the amide anesthetic group. It was found safe except in large quantities that generally exceeded 500 mg. It has a relatively short duration of action, usually lasting only several hours. Bupivacaine is a second-generation amide anesthetic that has a prolonged duration of action. It is, however, associated with more cardiac and neurotoxic reactions and has a maximum recommended safe dose of 150 mg. Because of the poorer cardiac profile of bupivacaine, third-generation amide anesthetics were developed. Ropivacaine is a member of this group that produces long-

term local anesthesia like bupivacaine but with a better cardiac profile. Injections of local anesthetic are small enough that one should generally never approach the maximum allowable dosages.

Bupivacaine and ropivacaine come in different concentrations (0.25, 0.5, and 0.75 % and 0.2 and 0.5 %, respectively). The lower dosages are useful for pain relief in epidural and nerve blockage injections. The more concentrated dosages will produce motor blockade, which is not wanted with these procedures.

Antibiotics

Antibiotics are needed for only selected procedures in spine intervention. These include discography, intradiscal electrothermal therapy, percutaneous discectomy, vertebroplasty and kyphoplasty, and the implantation of pumps and stimulators. Most injection procedures do not require antibiotics. The purpose of antibiotic coverage in most of these procedures is to decrease the chance of seeding bacteria in poorly vas-cularized sites such as the disc or around foreign bodies (implantables). Since penicillin allergy is not uncommon, a broad-spectrum antibiotic with minimal or no penicillin cross-reactivity is generally chosen. Though some penicillin cross-reactivity with the cephalosporins exists, it is minimal and therefore a reasonable choice is cefazolin (Ancef). This is the most common antibiotic used for this purpose and is given in a 1 g dosage intravenously or intramuscularly (IV or IM) 30 minutes prior to the procedure. Additionally, it can be put into the contract for discographic procedures (usually 20-100 mg, with the upper range used when no IV antibiotics are given). It must be borne in mind that this antibiotic will cause grand mal seizure activity if given intra-thecally. No antibiotic should be injected if a transdural approach is employed.

In some patients, allergy or lack of access to an IV hookup may make alternate choices better. Another commonly utilized antibiotic in the interventional lab is ciprofloxacin (Cipro). This is a fluoroquinolone with a broad spectrum of coverage and without cross-reactivity to penicillin. It is usually given orally in dosages of 500 mg twice a day. It can be given intravenously (400 mg) but must be given slowly over a 60-minute period to avoid pain and IV site reaction. This generally limits its use in the lab to oral administration.

Another good alternative is levofloxacin (Levaquin), a fluorinated carboxyquinolone. It may be given orally or intravenously and has similar plasma and time profiles for both, making it a good choice for either route (again slow administration is required for IV use). The general dosage is 500 mg every 24 hours.

Analgesics

Conscious sedation, sometimes needed with a few procedures in the realm of image-guided spine pain management (e.g., percutaneous vertebroplasty), works fine while the patient is on the table. However, some procedures are frankly painful (e.g., discography), and others (e.g., epidural steroid injection) may be associated with a post-

procedural pain flare-up. If persistent pain occurs, one may need to prescribe analgesics appropriate for the patient's pain level and suspected duration. This will not usually take the form of long-term or chronic analgesic administration. The two mainstays for postproce-dural pain management are opioids, nonsteroidal anti-inflammatory (NSAID) drugs, or combination agents that contain drugs of both types.

Mild to intermediate pain may be handled by the use of NSAIDs alone or in combination with a weak opioid (codeine, hydrocodone, dihydrocodeine, oxycondone). Controlled trials show little difference in efficacy of the NSAID category, and therefore finding one that works will usually be sufficient. There is potential toxicity from the NSAIDs to the gastrointestinal, genitourinary, central nervous, and hematolog-ical systems. Consider avoiding NSAIDs in patients predisposed to developing gastropathy or bleeding diathesis. Ketoralac (Toridol) is very effective for short-term use in intermediate pain relief.8 It is recommended only for short-term use and should be administered with an initial IV or IM loading dose given prior to oral dosing. Multidose (IV or IM) administration recommended for patients less than 65 years is 30 mg every 6 hours, not to exceed 120 mg per day. For patients over 65, renally impaired patients, and those weighing less than 50 kg, the dosage is 15 mg every 6 hours, not to exceed 60 mg per day. If there is breakthrough pain, one should not increase the NSAID dosage but add additional analgesic coverage. Regular, rather than intermittent, therapy promotes both anti-inflammatory and analgesic effects.

Intermediate pain is often managed with the weaker opioids such as codeine, hydrocodone, dihydrocodeine, or oxycodone. These drugs are usually formulated as combination products and are weak only insofar as the inclusion of aspirin, acetaminophen, or ibuprofen results in a ceiling dose above which the incidence of toxicity increases. Prescribed alone, some of these drugs can manage even severe pain. Codeine is emetic and is prescribed much less than in the past. Hy-drocodone preparations (Vicodin, LorTab) are now more commonly used. The potency is between that of codeine and oxycodone. Hy-drocodone is not available as a single entity preparation. Oxycodone, now available as a combination product (e.g., Percocet, Percodan), as well as a single-entity preparation (e.g., Roxicodone, Percodone), is very effective. It also is now available in a slow-release formulation (Oxycontin) that is very potent.

The most potent opioids are reserved for severe pain (e.g., the intractable pain associated with cancer). The members of this group include morphine, controlled-release morphine (MS Contin), hydromor-phone (Dilaudid), meperidine (Demerol), and methadone (Dolophine). Oxycodone also falls somewhat within this category when used as a single-entity preparation.

Adjuvant Analgesics

Classic pain is usually well handled by one of the NSAIDs, an opi-oid, or a combination product. These analgesics effectively deal with pain resulting from classic nociceptor response to intense, potentially tissue-damaging stimuli. However, neuropathic pain results from spontaneous discharge of injured nerves. It may be enhanced by sympathetic afferent activity as well. This type of pain is not as easy to control with standard analgesics; successful treatment has been achieved by means of adjuvant drugs such as antidepressants and an-ticonvulsants.

When neuropathic pain is described as burning and constant, the tri-cyclic antidepressants become the first line of therapy. Syndromes such as postherpetic neuralgia and phantom limb pain are examples. Amitriptilyne (Elavil) is the most widely studied drug used for this type of dyesthetic pain. The operative mechanism for antidepressant-mediated analgesia is believed to be the increase in circulating pools of norepinephrine and serotonin created by reductions in the postsyn-aptic uptake of these neurotransmitters. The quantities of drug administered are well below what is needed to relieve depression and suggest a separate mechanism of action.

When neuropathic pain is described as intermittent but sharp and lancinating, anticonvulsant drugs have been used with success and should be tried before the antidepressants. It is believed that they relieve pain by damping ectopic foci of electrical activity and spontaneous discharge from injured nerves. Though carbamazepine and phenytoin have been useful as adjuvant analgesics, gabapentin (Neurontin) is a new anticonvulsant that has been found to be effective for neuropathic pain relief while avoiding most of the side effects found with the other anticonvulsants.

These and other adjuvant analgesics should be used when neuropathic pain contributes to a patient's discomfort.

Radiographic Contrast Agents

Always an area of potential controversy for the image-guided physician, the choice of an appropriate contrast agent is challenging. The main concern is related to allergic potential and use within the thecal sac. There is no method that completely avoids the potential for allergy. Premedication is indicated in all patients with known allergy or prior reaction. If that reaction was severe, then all methods should be used to avoid the use of iodinated contrast. Substitution of another type of material may be useful (e.g., gadolinium). Pretreatment should include oral corticosteroids (prednisone, 50 mg, 13, 7, and 1 hours before the procedure), and oral H1 and H2 blockers 1 hour before the procedure (diphenhydramine, 50 mg; tagamet, 300 mg).9

Although allergic reaction to nonionic contrasts exists, it may be lower than the incidence found with the ionic media. Routine use of nonionic contrast (Isovue, Omnipaque, Optivist, Optiray) is effective and safe for facet and sacroiliac joint injections. However, when there is a chance of injection into the thecal sac (e.g., epidural steroid injections), an agent that is approved for intrathecal use is recommended (Isovue M-200, Isovue M-300).

Neurolytic (Cytotoxic) Agents

Chemical and thermal agents intended for neurolysis have been used for decades.10 Commonly used agents or procedures include absolute alcohol, phenol, cryoanalgesia, and radiofrequency lesions. These materials or methods are intended to create long-term or permanent damage. This must be taken into account when one is planning therapy and discussing the procedure with the patient.

Absolute alcohol is commercially available as a 95% concentration. Its use at this concentration is very painful, and therefore substantial sedation or anesthesia is necessary during injection. Being hypobaric to cerebrospinal fluid (CSF), alcohol rises if injected into the thecal sac. When injected near the sympathetic chain, alcohol destroys the ganglion cells and blocks postganglionic fibers.11 Postinjection neuralgia, hypesthesia, or anesthesia can be side effects of alcohol use.

Phenol (carbolic acid), like alcohol, has been used extensively and for a long time.12 It is not available commercially as an injectable preparation but can be made by the hospital pharmacy. It has the advantage of causing much less local pain during injection than does absolute alcohol. Phenol is usually prepared in concentrations of between 4 and 10% and is hyperbaric to CSF. It is not stable at room temperature. Phenol produces a shorter and less intense blockade than does alcohol. Moller et al. estimated that 5% phenol was equivalent to 40% alcohol.13 In intractable pain, the analgesic effects of phenol and alcohol have been found to be equal.14

References

1. Bodduk B, Cherry D. Epidural corticosteroid agents for sciatica. Med J Aust 1985;143:402-406.

2. Dilke TfW, Burry HC, Grahame R. Extradural corticosteroid injection in management of lumbar nerve root compression. Br Med J 1973;2:635-637.

3. National Health and Medical Research Council. Epidural Use of Steroids in the Management of Back Pain. Canberra: Commonwealth of Australia; 1994.

4. Cicala RS, Turner R, Moran E, Henley R, Wong R. Methylprednisolone acetate does not cause inflammatory changes in the epidural space. Anes-thesiology 1990;72:556-558.

5. Delaney TJ, Rowlingson JC, Carron H, Butler A. Epidural steroids: effects on nerves and meninges. Anesth Analg 1980;58:610-614.

6. Abram SE. Epidural steroid injections for the treatment of lumbosacral radiculopathy. J Back Musculoskel Rehab 1997;8:135-149.

7. De Jong RH. Local Anesthetics. 2nd ed. St. Louis, MO: CV Mosby; 1994.

8. Patt RB. Pain management. In: Abram SE, Haddox DJ, eds. The Pain Clinic Manual, 2nd ed. Philadelphia: Lippincott Williams & Wilkins; 2000:293-351.

9. Pittman A, Castro M. Allergy and immunology. In: Ahya SN, Flood K, Paranjothi S, eds. Washington Manual of Medical Therapeutics. 30th ed. Philadelphia: Lippincott Williams & Wilkins; 2001;241-255.

10. Swetlow GI. Paravertebral alcohol block in cardiac pain. Am Heart J 1926;1:393.

11. Merrick RL. Degeneration and recovery of autonomic neurons following alcohol block. Ann Surg 1941;113:298.

12. Putman TJ, Hampton OJ. A technique of injection into the Gasserian ganglion under roentgenographic control. Arch Neurol Psychiatr 1936;35: 92-98.

13. Moller JE, Helweg J, Jacobson E. Histopathological lesions in the sciatic nerve of the rat following perineural application of phenol and alcohol solutions. Dan Med Bull 1969;16:116-119.

14. Wood KA. The use of phenol as a neurolytic agent: a review. Pain 1978; 5:205-229.

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  • Isaia
    What is the difference between biplane and single plane angiography?
    8 years ago

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