Management of Pain by Anesthetic Techniques

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CHAPTER 158 Management of Pain by Anesthetic Techniques

Rajni K. Jutla, Grace Chen, Matthew McGehee, Brett R. Stacey

Most physicians who manage pain by anesthetic techniques believe these techniques are not stand-alone treatments, but rather an integral component in a comprehensive treatment approach. As the field of pain medicine matures, the role for neural blockade techniques using local anesthetics and steroids in the assessment and treatment of pain continues to be refined. This chapter reviews some of the more common techniques and related issues of current pain management.

Considerations for Diagnostic and Therapeutic Injections

Diagnostic Injection

Application of local anesthetics to nervous tissue decreases transmission of sensory and motor information by means of sodium channel blockade. Knowledge of neural innervation patterns and anatomy allows targeted injection of local anesthetics (Figs. 158-1 and 158-2). If effective, the temporary pain relief that lasts until the local anesthetic blockade is reversed provides the basis for diagnostic injections. The blockade assists in confirmation of location of underlying pathology, or confirmation of mechanism, as seen in sympathetically mediated pain.

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FIGURE 158-1 Anteroposterior view of a celiac plexus block.

(Courtesy of Brett Stacey, Oregon Health & Science University School of Medicine, Portland, OR.)

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FIGURE 158-2 Lateral view of a celiac plexus block.

(Courtesy of Brett Stacey, Oregon Health & Science University School of Medicine, Portland, OR.)

When an injection or any interventional procedure is the basis for diagnosis or future treatment, careful attention to patient selection, technique, and process is critical.1 The patient must understand in advance that the injection is intended as a diagnostic or prognostic maneuver, not as therapy. A general approach to diagnostic injections is summarized in Table 158-1.

TABLE 158-1 Guidelines for Diagnostic Neural Blockade

1 Document sensory and motor function before and after the injection.
2 Document a preprocedure pain score (baseline), taking into account provocation of pain with movement, positioning, touch, or other stimuli.
3 Track pain relief afterward with a pain diary extended over several hours, including pain at rest and with provocation.
4 Maintain careful attention to technique and needle placement using the following:

a Fluoroscopy for all injections with anatomic bony landmarks
b Nerve stimulation for localization of peripheral nerves
c Radiographic contrast to ensure a lack of vascular uptake and appropriate spread only to intended target
d Atraumatic technique (e.g., small needles, minimal repositioning)
e Minimal infiltration of subcutaneous tissues with local anesthetic
f Minimal volume of injectate (often less than 1 mL when the needle is placed accurately)

5 Consider two diagnostic injections, possibly with different local anesthetics.
6 Consider the possibility for a placebo response at any stage of the procedure. Some authorities advocate a separate placebo injection.
7 Consider alternative diagnoses or explanations for the pain and the patient’s responses.

Therapeutic Injection

Therapeutic injections are based on the well-documented, frequently encountered, and not well-understood phenomenon of prolonged pain relief after local anesthetic injection. Prolonged pain relief may result from altered central nervous system function, altered muscle tonicity at the affected area, morphology of peripheral nerve physiology, or some as yet undiscovered mechanism.

The rationale for including corticosteroids in therapeutic injections is based on the principle that perineural inflammation accompanies painful conditions. The numerous anti-inflammatory and membrane-stabilizing properties of steroids may contribute to decreased sensitization, decreased edema, and pain relief when steroid is injected into the vicinity of painful nerves. Animal models demonstrate that steroids can beneficially modify the effects of neurogenic inflammation by decreasing thermal hyperalgesia,2 decreasing phospholipase A2 activity,3 inhibiting prostaglandin production,4 and blocking normal C-fiber firing.5

Limitations of Neural Blockade and Therapeutic Injection

Diagnostic and therapeutic injections are firmly entrenched in clinical pain management practice and serve as an important clinical tool. However, limited controlled studies, inconsistent outcome measures, variations in technique, and lack of universal standards limit their acceptance in the era of evidence-based medicine. Because of this, some have labeled the use of injection techniques as outdated or, at a minimum, less effective than other treatments.

Limitations Associated with Neural Blockade

Pain is a subjective experience; patient cooperation and feedback are the basis for interpretation of diagnostic neural blockade. There may be an incidence of placebo response or expectation bias as high as 35% with each injection.6,7 Physicians must be attentive to their own bias when discussing pending diagnostic procedures because the patient response may be influenced by physicians’ suggestions, expectations, and interactions.8,9

The patient may have more than one type of pain or source of pain that may confound the patient’s interpretation of the injection, leading to a partial response open to interpretation. Anatomic and physiologic variations may lead to incomplete block, block of unintended nerves, or lack of effectiveness.10,11 Postoperative changes may limit flow of injectate, obscure landmarks, or alter anatomy.

Limitations of Therapeutic Injections

The literature in support of therapeutic benefits to patients from neural blockade techniques is, unfortunately, quite limited. A variety of alternative treatments such as physical therapy, systemic analgesics, and psychological techniques are available for pain conditions, but few studies compare nerve blocks with the other conservative treatment options.

It is a rare occurrence when we can attribute chronic pain conditions to a single cause. There may be musculoskeletal factors, a psychosocial dynamic, or a functional loss that can influence the impact of the pain syndrome on the patient. In addition, universal neural blockade technique standards do not exist. For example, a patient referred for nerve blocks for the diagnosis of complex regional pain syndrome (i.e., reflex sympathetic dystrophy) of an upper extremity could receive an impressive variety of nerve-blocking techniques for this condition. Injection at the stellate ganglion with or without fluoroscopic guidance, a posterior paravertebral approach to the upper thoracic sympathetic chain, injection into the epidural space, performance of an intravenous regional anesthetic, and performance of a brachial plexus block are some of the options available for this condition. For each of these, local anesthetic, steroid, opioid, clonidine, guanethidine, reserpine, bretylium, or a variety of other medications could be employed.12,13

Imaging Guidance

Fluoroscopy

Fluoroscopy is an essential adjunct for performing neural blockade techniques. Fluoroscopy and radiopaque contrast material help to improve the safety and accuracy of needle placement before regional anesthetic or neurolytic interventions and to verify accurate neuraxial catheter or spinal cord stimulator electrode placement.

Most fluoroscopy units produce images with an image intensifier and have a “last image hold” function, which allows recalling the last image without having to again expose the patient to radiation. Many newer fluoroscopy units offer a “pulsed fluoro mode,” which is often used to follow the spread of contrast material in real time. In pulsed mode, the x-ray beam is pulsed rapidly on and off, resulting in a lower radiation dose compared with continuous fluoroscopy.14 Quick and easy correlation of surface anatomy with the radiographic image is allowed by use of a laser guidance system. This also decreases fluoroscopy time and radiation dose.

During fluoroscopy, contrast material provides opacification of blood vessels and tissues. Nonionic contrast agents such as iohexol, iotrolan, iomeprol, and iodixanol are water soluble and have a lower potential for central nervous system toxicity, renal impairment, or anaphylactoid reactions compared with ionic agents.15–18 Using fluoroscopy in the anteroposterior, lateral, or oblique views, the pattern of spread visualized after injecting contrast agent can be used to delineate different tissue planes and proper needle placement before the introduction of local anesthetic, steroids, or neurolytic substances.

Epidural steroid injections (ESIs) originally were performed using a “blind” technique without fluoroscopic guidance. Injecting variable amounts of radiologic contrast material under fluoroscopic observation before therapeutic injection improves safety and efficacy. White19 found that inaccurate needle placement occurred in 25% to 30% of blind injections, even in the hands of skilled and experienced proceduralists.

The ability to visualize the target may allow placement of the needle with fewer corrections in trajectory, reducing the time and trauma involved. Intravascular needle placement is quickly ascertained by rapid uptake and disappearance of contrast material injected under fluoroscopy before local anesthetic injection, diminishing the risk for toxicity. Finally, intrathecal spread of contrast appears more confluent and spreads farther than epidurally. This demonstration would be important to avoid a subsequent injection of anesthetic or steroid into the intrathecal compartment to avoid a spinal block or adhesive arachnoiditis, respectively.

Ultrasound

The modality of ultrasound imaging has been successfully adopted to perform peripheral nerve blocks and catheter placement in the field of regional anesthesiology. There is also some evidence that ultrasound guidance is useful when performing percutaneous pain procedures. Ultrasonography is free from radiation, is easy to use, and can provide real-time images to guide needle placement. Chen and coworkers20 found that when ultrasound was used to guide the epidural needle through the sacral hiatus while performing a caudal ESI, it was accurate 100% of the time when confirmed with contrast-dye fluoroscopy.

Chronic neck pain after whiplash injury is caused by trauma to the cervical zygapophyseal (facet) joints in about 50% of patients. Using ultrasound guidance in 14 volunteers, Eichenberger and coworkers21 were able to visualize and inject adjacent to the third occipital nerve when attempting to block the nervous supply of the C2-3 facet joint. Fluoroscopy, however, demonstrates only the bony adjacent structures, not soft tissue structures such as nerves. Finally, Gruber and associates22 performed neurosclerosis in 82 patients with residual limb neuroma using ultrasound guidance and reported that these patients appeared to have better outcomes than those who received injections without ultrasound guidance.

In addition, ultrasound guidance helps to verify correct needle placement and to rule out subcutaneous injection of potent opioid doses when an intrathecal drug delivery device (pain pump) needs to be refilled. Finally, pain practitioners use ultrasound when investigating the presence of septic pockets at sites of implanted devices such as the spinal cord stimulation generators or intrathecal drug reservoirs.

Epidural and Selective Nerve Root Injections

ESIs have been described as the “bread and butter” of injection treatment for neck, back, and radiculopathic extremity pain. Published studies and commentaries have emphasized the safety of ESIs but questioned the efficacy of the technique and highlighted the ubiquitous, nondiscriminant application of ESIs.23 Between 1996 and mid-2006, 69 ESI–related papers were published in the English-speaking medical literature. Prospective outcome studies are a small minority of these publications, whereas more than 50% are letters and reports of adverse events involving ESIs.24

No conclusive prospective, randomized outcome studies have demonstrated long-term benefit, and multiple studies have demonstrated an outcome similar to placebo after 2 weeks.24 The Wessex Epidural Steroids Trial (WEST)25 study group found that neither single nor multiple ESIs improved on placebo when pain outcomes were measured 35 days after injection. Despite these controversies, ESIs probably have an important role to play in selected patients, particularly those with radicular pain.26 The success of this important therapeutic procedure depends on attention to patient selection, technique, and concomitant therapies.

Rationale for Epidural Steroid Injections

It is well known that a herniated disk pressing on a nerve root can produce radicular pain. Inflammation may play a role in symptomatic nerve root irritation that is associated with herniated intervertebral disks.27 Proinflammatory substances are contained in extruded nucleus pulposus material and may produce an inflammatory response in the epidural space and in the underlying nerve roots.28–31 It is likely that pain and other symptoms are produced by a combination of this inflammatory response, edema, and the mechanical pressure on nerve roots.

Steroids can decrease neurogenic inflammation and produce membrane stabilization that results in pain relief, but the effect may take several days. In individuals who have symptoms, the epidural space can be very sensitive to any pressure or injection. Because of the delayed onset of this steroid effect, a rationale can be made for including a local anesthetic in the injection, decreasing the pain of the initial injection. The local anesthetic can also prognosticate the expected pain relief that may later derive from the steroid based on the patient’s experience of early relief of pain after the precise delivery of the local anesthetic–steroid mixture.

Indications, Contraindications, and Limitations

Radicular extremity pain that has not responded to more conservative treatment is the primary indication for ESI (Table 158-2). ESI is not indicated for the treatment of mechanical or muscular axial back pain. Outcome studies do not clearly support the use of ESIs in spinal stenosis patients,32 but many clinicians feel that they can be helpful in this population, particularly in patients with radicular symptoms. Benefit in patients with prior back surgery is less clear, but many believe a subset of these patients benefits from ESI as well.26

TABLE 158-2 Selection for Epidural Steroid Injection

INDICATIONS CONTRAINDICATIONS FACTORS ASSOCIATED WITH FAILURE
Herniated nucleus pulposus with extremity pain in a radicular pattern Anticoagulation
Infection at the site		 Smoking
Unemployed
Foraminal stenosis with radicular symptoms Other pain that is more intense Long duration
Spinal stenosis with extremity symptoms
Imaging studies with concordant findings
Lack of consent
Allergy to intended injectate

Unvarying pain despite activity or treatment Pain present for weeks to months Relative contraindications include primarily back pain, failed prior epidural steroid injections, untreated anxiety or depression Psychological distress
Nonradicular pain

Adapted from Hopwood MB, Abram SE. Factors associated with failure of lumbar epidural steroids. Reg Anesth. 1993;18:238-243; and Jamison RN, VandeBoncouer T, Ferrante FM. Low back pain patients unresponsive to an epidural steroid injection: Identifying predictive factors. Clin J Pain. 1991;7:311-317.

Hwang and colleagues33 reported in a prospective, nonrandomized study that ESI is helpful in treating the pain of acute herpes zoster virus (HZV) infection. Manabe and associates34 demonstrated that in addition to systemic antiviral treatment, an epidural infusion with local anesthetic was superior to saline in a prospective randomized trial at reducing pain and allodynia. ESIs administered during the acute stage can be used for the prevention of postherpetic neuralgia (PHN) and shorten the duration of pain.

Interlaminar versus Transforaminal

In a small study, Thomas and colleagues35 compared loss-of-resistance interlaminar ESI with fluoroscopically guided transforaminal ESI and found improved pain relief, functional, and quality-of-life indicators 6 months after injection in the transforaminal group. In addition, Ackerman and Ahmad36 studied 90 patients with L5-S1 disk herniation and found that the transforaminal route of administration was superior to the caudal and interlaminar routes.

Injection Technique

The goal of the injection is to deliver steroid as a single agent or combined with local anesthetic to the presumed source of pain and symptoms. Delivery techniques vary widely, and a variety of solutions and volumes are commonly used.37 Two very common techniques in widespread use are the parasagittal or midline interlaminar and the transforaminal approaches.

Interlaminar and Caudal Injection Techniques

For labor analgesia and perioperative anesthesia and analgesia, the epidural space is typically accessed using the loss-of-resistance technique with an interlaminar approach as the patient assumes a sitting or lateral decubitus position. The disadvantage is that the medication is delivered into the center of the posterior epidural space instead of being directed at the level and laterality of the suspected pathology. However, when combined with the use of contrast injection and multiplanar fluoroscopy, the technique has diagnostic value (the patency of foraminal openings, level of scarring, and spread of injectate are all seen with fluoroscopy) and the ability to ensure that the injectate has been delivered to the epidural space.

Without the use of fluoroscopic guidance, failure to achieve injection into the epidural space has been reported to be as high as 12% to 38%.37,38 A prospective study of patients with previous back operations demonstrated a failure rate of 53% in placing an epidural needle at the desired level based on surface anatomy alone and only a 26% success rate in delivering injectate to the level of pathology.37 In a retrospective study, Johnson and colleagues39 demonstrated that combining epidurography with ESI permitted safe and accurate therapeutic injections with an exceedingly low incidence of complications.

Commonly, a specialized epidural needle such as a 17- to 22-gauge Tuohy or a Crawford needle, coupled with the loss-of-resistance technique, is employed to locate the epidural space. Sometimes, an epidural catheter inserted through the needle is used to direct the medication delivery to a more cephalad target, such as a cervical nerve root through a T1-2 interspace. Finally, the lumbar epidural space may also be accessed caudally through the sacral hiatus using a catheter (e.g., Racz) that is cannulated through the needle and advanced cephalad.

Transforaminal Injection Technique

With the transforaminal technique, the epidural space is accessed at the neuroforamen yielding the index spinal nerve. This approach describes contrast spread that is intended to be more medial to ascend and descend in the epidural lateral gutter. However, the selective nerve root ESI represents an injection through a similar approach but with contrast outlining the nerve root and spreading laterally along its shaft. Nonetheless, correct application of the technique requires the use of fluoroscopy because surface landmarks and tactile sensations are unreliable in ensuring appropriate final needle position.

With the patient in a prone position, the primary lumbar landmarks for performing this injection are the transverse process above the desired nerve root representing the superior aspect of the neuroforamen. The target area is referred to as the safe triangle because it does not contain neural structures and therefore limits the opportunity for direct nerve damage from the needle40 (see “Fluoroscopy” earlier).

Typically, a 3- to 6-inch, 22- to 25-gauge needle is used with or without an introducer needle. We use a curved needle technique, in which the distal aspect of the needle is curved away from the bevel opening. This technique provides improved steering to the needle for arriving at the target and navigating around sensitive structures such as the nerve root. Needle position is confirmed using radiographic contrast injection; then, a combination of local anesthetic and steroid is injected.

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