Chapter 5 Epidural Blocks

Epidural nerve block consists of the administration of small volumes of target-specific local anesthetics, corticosteroids, and other agents into the epidural space to interrupt the pain spasm cycle and reduce inflammation of either axial or radicular pain (Boxes 5.1 and 5.2; Table 5.1) [1,2]. These agents are injected through one of three approaches—interlaminar (for cervical, thoracic, and lumbar epidural injections), transforaminal (for cervical, thoracic, and lumbosacral injections), or caudal. The transforaminal block is discussed in Chapter 6.

BOX 5.1 The Concept of Epidural Injections

Approaches: interlaminar, transforaminal, caudal

Target structure: epidural space, especially the ventrolateral area

Agents administered:

Local anesthetics, which interrupt both the pain spasm cycle and reverberating nociceptor transmission

Corticosteroids, which reduce inflammation by inhibiting the synthesis or release of a number of pro-inflammatory substances

Target symptom: axial or radicular pain

Table 5.1 Postulated Mechanisms of Neural Blockade and Corticosteroids

Injections can also be performed under fluoroscopic guidance and with use of a contrast agent in order to deliver cortisone as close to the disc herniation, area of stenosis, or nerve root impingement, as determined by MRI or CT, and with as little morbidity as possible.

Neural blockade alters or interrupts the following (see Table 5.1):

Nociceptive input

Reflex mechanisms of the afferent limb

Self-sustaining activity of the neuron pool and neuraxis

The pattern of central neuronal activities

Neural blockade may be achieved with local anesthetics or corticosteroids (see Table 5.1). Local anesthetics interrupt the pain spasm cycle and transmission by reverberating nociceptors. Corticosteroids reduce inflammation by (1) inhibiting the synthesis or release of a number of pro-inflammatory substances or (2) causing a reversible local anesthetic effect.

The various modes of action of corticosteroids are as follows (see Table 5.1):

Membrane stabilization

Inhibition of neural peptide synthesis or action

Blockade of phospholipase A₂ activity

Prolonged suppression of ongoing neuronal discharge

Suppression of sensitization of dorsal horn neurons

The benefits of neural blockade can outlast the duration of the anesthetics used. This occurs by the following mechanisms:

Influence on the sympathetic nerve system

Temporary abolition of spontaneous ectopic discharges, resulting in suppression of dynamically maintained central hyperexcitability, as well as reinforcement of endogenous G-protein-couple receptor inhibition of N-type voltage-sensitive calcium channels

Glial inactivation

The presumed effect of steroids is to reduce:

Neuropathic pain

Inflammation

Swelling

Scarring

The mechanism of radiculopathy–neuropathic pain and the action of epidural steroid injection

The rupture of the anulus fibrosus causes radiculitis either by mechanical pressure from disc protrusion or by chemical irritation of the nerve root by leaking material from nucleus pulposus (phospholipase A₂) resulting in radiculopathy-neuropathic pain. In a neuropathic pain state, the steroids can decrease the conduction in injured nerves. It also has been observed that steroids can reduce the bulk of a scar by diminishing its hyaline portion, while leaving the fibrous skeleton intact. Tables 5.2 and 5.3 list profiles of, formulations for, and adverse effects of the commonly used epidural steroids.

Table 5.2 Profile of Commonly Used Epidural Steroids

Table 5.3 Formulations of Commonly Used Epidural Steroids and Their Adverse Effects on the Nerves

As already mentioned, the three main approaches for epidural steroid injection (ESI) are transforaminal, the most specific and effective route; interlaminar, via a midline or paramedian approach; and caudal (see Box 5.1).

The potential uses of fluoroscopically guided transforaminal ESIs include:

Treatment of intraspinal inflammation causing axial spine or radicular pain

Management of acute, subacute, or chronic axial spine or radicular pain that is refractory to more conservative care such as rest, analgesics, and physical therapy

Efficacy of the treatment/procedure is signified by the following:

Reduced leg pain, improved leg raising, and improved lumbar flexion are found at 2 weeks after injection.

No pain-related or functional benefits are seen at 4 weeks or 1 year after injection.

Possible problems with epidural blockade

The injection variables that can affect target site concentration are as follows:

ESI performed without fluoroscopic guidance

The presence of epidural plica or scarring

The volume of the injectate

The rate or pressure of the injection

ESI should not be performed without fluoroscopic guidance. The potential risks of performing ESI without fluoroscopic guidance are as follows:

Intraneural injection

Technical difficulty in the presence of spinal fusion or hardware

Intravascular injection

Spinal cord trauma

Failure to deliver medication to the treatment field may be related either to the approach or to patient variables, as follows:

Epidural fibrosis can result in the preferential flow of medication away from a recurrent disc herniation.

Caudal injections may fail to deliver medication above L5-S1, particularly in patients with central canal stenosis.

Interlaminar injection may localize preferentially to the dorsal epidural space.

Transforaminal injections may localize preferentially to the peripheral perineural space particularly in the setting of severe foraminal stenosis.

Procedural morbidity also varies with each approach. With interlaminar injections, there is a risk of intrathecal injection and subsequent arachnoiditis as well as postprocedural headache. Patients receiving transforaminal injections frequently report significant, although in most cases transient, leg pain, and there is a risk of spinal cord infarction.

Recommendations for use

The American Society of Interventional Pain Physicians makes the following recommendations:

Injections should be given at intervals of 2 weeks only as necessary according to medical necessity criteria.

A maximum of 6 injections per body region should be given per year.

All regions should be treated at the same time, if feasible.

The International Spinal Injection Society recommends that no more than 4 injections at intervals of at least 7 to 14 days be given within a 6-month period.

A definite trend toward nonsurgical management of lumbosacral disc herniation with radicular symptoms has been noted. [3] This change is appropriate for the following reasons:

Resorption of lumbar herniated disc fragments can occur.

Some lumbar disc disorders are asymptomatic, including herniations.

There is an inflammatory component to low back and/or radicular pain in the presence of disc herniation; an inflammation reaction may be necessary to precipitate symptoms, even in the presence of mechanical compression.

The contents of the epidural space

The contents of the epidural space are fat, epidural veins and arteries, and lymphatics (Fig. 5-1).

Figure 5–1 Cross-sectional (A) and three-quarters (B) views of the anatomy of the epidural space.

Fat acts as:

A shock absorber for thee other contents of the epidural space and the dura contents of the dural sac.

A depot for drugs injected into the epidural space.

The epidural veins:

Are concentrated primarily in the anterolateral portion of the epidural space.

Are valveless and thus transmit both intrathoracic and intraabdominal pressures.

Serve the entire spinal column, so they are a ready conduit for the spread of hematogenous infection.

The epidural arteries lie primarily in the lateral portions of the epidural space. Lymphatics are concentrated in region of dural roots, where they help remove foreign material from the subarachnoid and epidural spaces.

Contraindications

Contraindications to epidural nerve block are as follows:

Local infection

Sepsis

Anticoagulant therapy or coagulopathy

Hypovolemia (relative contraindication)

Complications

Complications related to needle placement and drug administration are as follows [4]:

Dural puncture, subdural injection, intravascular injection, spinal cord trauma, intracranial air injection, nerve damage, pneumothorax, vascular injury

Infection, abscess formation, hematoma formation, epidural lipomatosis, cerebral vascular or pulmonary embolus, headache, increased intracranial pressure, brain damage, death

Adverse effects of steroids (Tables 5.5 and 5.6) [2]

Table 5.5 Potential Side Effects or Complications of Epidural Steroid Administration

Endocrine	Adrenal suppression, hypercorticism, cushingoid syndrome, hyperglycemia, precipitation of diabetes mellitus, immunosuppression, hypokalemia, amenorrhea, menstrual disturbances, retardation of growth
Cardiovascular	Hypertension, fluid retention, congestive heart failure, deep vein thrombosis
Musculoskeletal	Osteopenia/osteoporosis, avascular necrosis of bone, pathologic fracture, muscle wasting and atrophy, muscle pain, joint pain
Psychological	Mood swings, insomnia, psychosis, anxiety, euphoria, depression
Gastrointestinal	Ulcerative esophagitis, hyperacidity, peptic ulceration, gastric hemorrhage, diarrhea, constipation
Ocular	Retinal hemorrhage, posterior subscapular cataracts, increased intraocular pressure, exophthalmos, glaucoma, damage to optic nerve, secondary fungal and viral infections
Dermatologic	Facial flushing, impaired wound healing, hirsutism, petechiae, ecchymosis, hives, dermatitis, hyper/hypopigmentation, cutaneous atrophy, sterile abscess
Metabolic	Hyperglycemia, glycosuria, redistribution of fat, negative nitrogen balance, sodium and water retention
Nervous system	Headache, vertigo, insomnia, restlessness, increased motor activity, ischemic neuropathy, seizures
Other adverse effects	Epidural lipomatosis, fever

Table 5.6 Characteristics of Adrenal Insufficiency (AI)

Type	Cause(s)	Endocrinologic Features
Tertiary (most common form)	Usually from iatrogenic corticosteroid therapy and suppression of the hypothalamic-pituitary-adrenal axis	Hypothalamic/pituitary suppression or absence
Secondary (uncommon)	Decrease or absence of ACTH (may be panhypopituitary or anterior pituitary dysfunction)	ACTH-dependent AI
	Pituitary depression, dysfunction/damage	Signs and symptoms usually due to loss of glucocorticoid function
	Tumor	Mineralocorticoid function usually intact
	Postpartum	Renal hypovolemia, more commonly hypoglycemia
Primary (rare)	Autoimmune (70%-90%)	ACTH-independent AI
	Infection	Increased ACTH production
	Inflammation	Possible hyperpigmentation
	Cancer (breast, lung, melanoma)
	Acute addisonian crisis

ACTH, adrenocorticotropic hormone.

Preoperative preparation

The patients who are suffering from axial pain on the spine and radicular pain on extremities according to the dermatome are candidates for epidural nerve block (Figs. 5-2 to 5-5).

Figure 5–2 Cervical dermatome chart.

(From Waldman SD. Physical Diagnosis of Pain: An Atlas of Signs and Symptoms. Philadelphia, Elsevier Saunders, 2006, pp 20-33.)

Figure 5–3 (A) C5, (B) C6, (C) C7, and (D) C8 dermatome distribution.

(From Waldman SD: Physical Diagnosis of Pain: An Atlas of Signs and Symptoms. Philadelphia, Elsevier Saunders, 2006, pp 20-33.)

Figure 5–4 Lumbar dermatomal chart.

(From Waldman SD: Physical Diagnosis of Pain: An Atlas of Signs and Symptoms. Philadelphia, Elsevier Saunders, 2006, pp 235-42.)

Figure 5–5 L4, L5, and S1 dermatome distribution.

(From Waldman SD: Physical Diagnosis of Pain: An Atlas of Signs and Symptoms. Philadelphia, Elsevier Saunders, 2006, pp 235-42.)

Physical Examination

Physical examination of a patient who is a candidate for epidural nerve block includes the following maneuvers and activities, which are described in more detail in the corresponding tables:

1. Spurling maneuver, which is a test of cervical nerve root compression or irritation that involves extension and rotation of the head to either side. Reproduction of radicular pain into the affected ipsilateral extremity with this head movement is considered a positive result. This text exhibits poor sensitivity (30%) but good specificity (93%).

2. Dural tension signs:

a. Straight-leg raise test, which is performed by elevation of the leg, with knee extended, and assessment of reproduction of pain into the leg with this movement. The result is positive if pain occurs between 30 and 70 degrees of elevation.

b. Looking for Lasegue sign, or performing Bragard test: The patient is supine. With one hand, the examiner grasps the patient’s 90°-flexed knee and palpates the lateral and medial joint cavity with thumb and index finger. With the other hand, the examiner grasps the patient’s foot and rotates the patient’s lower leg. Pain felt over the joint cavity indicates a meniscus lesion.

3. Determining whether the lesion causing pain in the arm or leg is in the root or the nerve (Table 5.7).

4. Testing of muscular strength (Tables 5.8 and 5.9).

5. Testing of tendon reflexes (Tables 5.10 and 5.11; Fig. 5-6).

Table 5.7 Clinical Manifestations of Root and Nerve Lesions in the Arm and Leg

Table 5.8 The Important Muscle Groups and Motions Associated with Cervical and Lumbar Myotomes

Root	Muscle Group(s) and Motion(s)
C5	Elbow flexors, shoulder abductors and external rotators
C6	Elbow flexors, wrist extensors and pronators, shoulder external rotators
C7	Elbow extensors, wrist pronators
C8	Extension of index finger, finger abduction and flexion, abduction of thumb, wrist flexion
T1	Finger abduction
L2	Hip flexion
L3	Hip flexion, hip adduction, knee extension
L4	Knee extension, ankle dorsiflexion
L5	Ankle dorsiflexion, great toe extension, ankle eversion, hip abduction and internal rotation
S1	Ankle plantarflexion

Table 5.9 Five-Point Scale for Grading of Muscle Strength

Grade	%	Definition
5	100	Active movement against full resistance (normal strength)
4	75	Active movement against gravity and some resistance
3	50	Active movement against gravity
2	25	Active movement with gravity eliminated
1	10	Trace movement or barely detectable contraction
0	0	No muscular contraction identified

Table 5.10 Deep Tendon Reflexes and Their Roots

Reflex	Root(s)
Biceps	C5, C6
Brachioradialis	C5, C6
Triceps	C6, C7
Patellar tendon	L2, L3, L4
Medial hamstring	L5, S1
Ankle jerk (Achilles tendon)	S1

Table 5.11 Scale for Grading Deep Tendon Reflex Responses

Grade	Response
0+	None
1+	Sluggish
2+	Active or normal
3+	More brisk than expected, slightly hyperactive
4+	Abnormally hyperactive, with intermittent clonus

Figure 5–6 A deep tendon reflex examination. (2+: normo-active)

(From Waldman SD: Interventional Pain Management, 2nd ed. Philadelphia, WB Saunders, 2001, p 94.)

Imaging Diagnosis

Figure 5-7 summarizes the imaging diagnosis.

Figure 5–7 Indentation of dural sac at C5-C6 disc level and mild disc bulging in C3-C4 on sagittal T2-weighted MR image (A) and T1-weighted image (B) is shown. Left paramedian disc protrusion of C5-C6 level on axial T2-weighted MR image (C) and T1-weighted image (D) is identified.

Preoperative Medication

Preoperative medication for an epidural nerve block consists of the following:

Weak opioid with acetaminophen, nonsteroidal anti-inflammatory drugs (NSAIDs)

Muscle relaxant

Gabapentin

Instrumentation

Equipment needed for an epidural nerve block is as follows:

Two different lengths (6 or 10 cm) of 23 gauge epidural needles are used depending on the location of insertion

2- or 5-mL well-lubricated sterile glass syringe for testing of epidural space using the loss-of-resistance or hanging-drop method

26-gauge needle for skin infiltration

Dressing set with antiseptics

Gauze and bandage

Fluoroscope if necessary

Drugs needed for the procedure are as follows:

0.2% lidocaine (dilution of 2% lidocaine), 0.2% ropivacaine, and 0.2% bupivacaine (dilution of 0.5% bupivacaine)

Steroids and ample normal saline

2% lidocaine for skin infiltration

Contrast media, if necessary

Other resuscitation drugs

Procedures

The procedures for epidural blocks are described here [5–7].

Cervical and Thoracic Epidural Block through the Interlaminar Midline Approach without Fluoroscopic Guidance

The procedure for a cervical or thoracic epidural block via the interlaminar midline approach is as follows:

1. The patient is placed in the sitting (or lateral) position, with the cervical spine flexed and the forehead placed on a padded bedside table. The skin is prepared with an antiseptic solution.

2. At the C5-6 or C6-7 interspace for the cervical spine, or the C7-T1 to T11-12 interspace for the thoracic spine, the operator’s middle and index fingers are placed on each side of the spinous processes.

3. The position of the interspace is confirmed with palpation using a rocking motion in the superior and inferior planes.

4. 1 mL of local anesthetic is used to infiltrate the skin, subcutaneous tissues, and the supraspinous and interspinous ligaments at the midline with a 26-gauge needle for skin infiltration.

5. A 6-cm-long, 23-gauge epidural needle for the cervical spine (see Fig. 5-8), or a 10-cm-long, 23-gauge epidural needle for the thoracic spine, is inserted exactly in the midline through the previously anesthetized area into the interspinous ligament.

6. The right-handed operator holds the epidural needle firmly at the hub with the left thumb and index finger. (Left and right directions in this description are reversed for a left-handed operator.) The operator places the left hand firmly against the patient’s neck to ensure against uncontrolled needle movements. As soon as the needle enters into the ligament flavum, the operator can feel the sensation of hardness and it becomes difficult to advance the needle with the left hand only.

7. The stylet of the needle is removed.

8. While applying constant pressure to the plunger of the glass syringe with the thumb of the right hand, the operator uses the left hand to advance the needle and syringe continuously in a slow and deliberate manner.

9. There will be a sudden loss of resistance to injection and the plunger will effortlessly surge forward.

10. The syringe is gently removed from the needle.

11. When satisfactory needle position is confirmed, the physician waits for 10 seconds or aspirates gently to identify leakage of cerebrospinal fluid (CSF) or blood.

12. A syringe containing 4-6 mL for the cervical spine, or 6-8 mL for the thoracic spine, of a mixture of local anesthetic and steroid is carefully attached to the needle.

13. The anesthetic mixture is injected. The force required for injection should not exceed that necessary to overcome the resistance during injection.

14. After injection of the mixture, a small volume of normal saline is injected to wash out the contents of the needle.

15. The stylet is inserted and the needle is removed.

16. A compressive dressing is applied; it may be removed after the first day.

17. The patient lies on the affected, symptomatic extremity for 10 minutes and then in the supine position for 20 minutes.

18. The patient is discharged after confirmation of no motor blockade and when vital signs are stable.

Figure 5–8 Axial (A) and sagittal (B) schematic drawings of a cervical epidural block through the midline via the interlaminar midline approach without fluoroscopic guidance.

Thoracic Epidural Block through the Interlaminar Paramedian Approach without Fluoroscopic Guidance

Figure 5-9 illustrates a thoracic epidural block using an interlaminar paramedian approach.

Figure 5–9 Axial (A) and sagittal (B) schematic drawings of a thoracic epidural block through the interlaminar paramedian approach.

Lumbar Epidural Block through the Interlaminar Midline Approach without Fluoroscopic Guidance

Figures 5-10 to 5-13 illustrate a lumbar epidural block using the interlaminar midlline approach.

Figure 5–10 The lumbar epidural space is bounded anteriorly by the posterior longitudinal ligament and posteriorly by the vertebral laminae and the ligamentum flavum.

Figure 5–11 When performing thoracic epidural block in the midline, the needle traverses the skin and subcutaneous tissues, and then the styletted epidural needle impinges on the supraspinous ligament, which runs vertically between the apices of the spinous process.

Figure 5–12 The vertebral pedicles and intervertebral foramina form the lateral limits of the epidural space. The lumbar epidural space is 5 to 6 mm at the L2-L3 interspace with the lumbar spine flexed. The lumbar epidural space contains fat, veins, arteries, lymphatics, and connective tissue.

Figure 5–13 The 3.5-inch, 18- or 20-gauge Hustead needle is inserted exactly in the midline in the previously anesthetized area, through the ligamentum nuchae into the interspinous ligament.

Caudal Epidural Block with Patient in the Prone Position

Figures 5-14 to 5-17 illustrate the following procedure for a caudal epidural block with the patient in the prone position

1. The patient is placed in the prone position, and the legs and heels are abducted to prevent tightening of the gluteal muscles. Preparation of a wide area of skin with antiseptic solution is carried out so that all of the landmarks can be palpated aseptically.

2. The middle finger of the patient’s nondominant hand is placed over the sterile drape into the natal cleft with the fingertip at the tip of the coccyx.

3. After the sacral hiatus is identified, a 6- or 10-cm-long, 26-gauge needle is inserted through the anesthetized area at a 45-degree angle into the sacrococcygeal ligament.

4. As the sacrococcygeal ligament is penetrated, the operator will feel a “pop.” If contact with the interior bony wall of the sacral canal occurs, the needle should be withdrawn slightly; this maneuver will disengage the needle tip from the periosteum.

Figure 5–14 The triangular sacrum consists of the five fused sacral vertebrae, which are dorsally convex.

Figure 5–15 The sacral canal contains the inferior termination of the dural sac, which ends between the S1 and S3 vertebrae.

Figure 5–16 A. After the sacral hiatus is identified, a 26-gauge needle is inserted through the anesthetized area. B. As the sacrococcygeal ligament is penetrated in 45-degree angle, the operator will feel a “pop.”

Figure 5–17 Anatomy of the sacrum and coccyx.

Caveats

The following issues should be kept in mind during an epidural block:

If the patient experiences any significant pain or there is a sudden increase in resistance during injection, the needle position may be incorrect; the injection should be stopped immediately for reassessment of the position of the needle.

If cerebrospinal fluid is aspirated, the epidural block should be postponed.

If aspiration of blood occurs, needle placement should be adjusted.