Complications of Common Selective Spinal Injections: Prevention and Management

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6 Complications of Common Selective Spinal Injections

Prevention and Management

Robert E. Windsor, MD, FAAPMR, FAAEM, FASPM, Elmer G. Pinzon, MD, Herman C. Gore, MD

Selective spinal injections are being performed with increasing frequency in the management of acute and chronic pain syndromes.¹^–³ Because these procedures require placing a needle in or around the spine, a risk of complications is always present. Therefore, knowledge about prevention of complications, and early recognition and management when they do occur, are paramount to appropriate patient care. This requires adequate physician training and appropriate patient preparation and monitoring. This chapter will discuss physician training, patient preparation and monitoring, and specific complications and their treatment (Appendix II).

Physician Training

The level of physician training required to safely perform selective spinal injections is a topic of debate. This debate is fueled by differing standards from one region of the country to another, and from one specialty to another. Some people are concerned, for example, that certain physicians are performing selective spinal injections without appropriate training, thereby placing their patients at undue risk.

Although it is true that uncomplicated lumbar procedures (in an otherwise healthy population) do not require the degree of training and expertise that high-risk procedures performed in a medically unstable population do, certain standards must still be met. Currently, the American Academy of Physical Medicine and Rehabilitation (AAPM&R) has adopted guidelines that recommend a minimum level of documented didactic and clinical training in complication prevention, recognition and management, spinal injection technique, and patient selection, such as that provided in an appropriate fellowship or residency program.⁴ This program must provide specific training in spinal injections and the recognition, prevention and treatment of related complications; and advanced cardiac life support (ACLS) certification.

In addition, the residency chairman or fellowship director must be confident in the abilities of the physician in question, prior to recommending his or her approval for spinal interventions. Specifically, selective spinal injection courses alone, although valuable, do not provide enough training (or depth of training) for the novice injectionist to safely perform spinal injections in practice.

Patient Preparation

Patient preparation issues include patient education,^5,⁶ informed consent statement, NPO (nil per os; “nothing by mouth”) status, IV access, certainty that no procedural contraindications exist, patient positioning, sterile preparation and draping, supplemental intravenous (IV) fluids and oxygen, and plans for appropriate recovery following the procedure. Depending on the procedure and patient status, prophylactic antibiotics may also be included.

Patient education should include a thorough description of the procedure, including potential risks, benefits, alternatives, and likely outcomes.⁶ An informed consent statement, confirming the conversation, should be executed. The statement should include signatures of the patient, the doctor, and a witness.

Prior to the procedure, the patient should be NPO for 12 hours for solid foods and for 8 hours for fluids, preoperatively, to ensure that all gastric contents are distal to the ligament of Treitz.⁷

A large-bore IV (ideally 20 guage or larger) should be started in a large proximal upper-extremity or neck vein. This is to allow immediate IV access in an emergent setting. Small-gauge or peripherally-placed IV catheters do not allow adequate access to the central venous supply for resuscitative purposes when peripheral vasoconstriction occurs.

Procedural contraindications or relative contraindications that may not have been present or recognized during the last physician office visit should be evaluated, such as chest pain, shortness of breath, fever, systemic infection, uncontrolled hypertension or other medical problems.

If the procedure involves placement of a needle or other instrument into a disc, or implantation of a device, then preprocedure laboratory work should be performed. In addition, if the patient is recovering from a known systemic infection (e.g., pneumonia or urinary tract infection), then preprocedure laboratory work should also be performed.

If the patient has coexisting medical problems (e.g., has chronic obstructive pulmonary disease [COPD], heart disease, etc.), clearance from the patient’s primary care or specialty doctor should be obtained. Depending on the patient’s problem, preprocedure laboratory work may include a complete blood count with differential diagnosis, liver function tests, urinalysis, chest radiograph, ECG, blood culture and sensitivity, urine culture and sensitivity, and erythrocyte sedimentation rate.

The patient should be positioned on the procedure table in a comfortable manner that will allow the treating physician unencumbered access to the region of the patient’s body under treatment. The patient’s position should be comfortable enough for him or her to lie still for the duration of the procedure.

Care must be taken to ensure there is no region of neural compression or stretch, particularly if sedating medication will be used. Areas that are particularly vulnerable to neural compression or stretch include the ulnar nerve at the elbow and the brachial plexus.⁸ If necessary, use an arm board, tape, strapping or padding to make the patient more comfortable, enable him or her to hold the appropriate position, and prevent the patient’s hands from inadvertently compromising the sterile field.

Sterile preparation should minimally include scrubbing the region of the body to be treated and surrounding areas with a povidone-iodine preparation and allowing it to dry. If the patient has an iodine allergy, chlorhexidine gluconate and/or isopropyl alcohol should be used. For discography or any type of implant, use a triple scrub, including isopropyl alcohol, chlorhexidine gluconate, and povidone-iodine, lasting for at least 5 minutes. Allow the povidone-iodine to dry. For these procedures, use pre- and postprocedure antibiotics, as well.

The degree of sterile draping required depends on the procedure. If a lumbar epidural is being performed, draping the immediate area around the penetration with sterile towels is adequate. If a spinal implant, percutaneous discectomy, or other more invasive spinal procedure is being performed, full-body draping with a fenestrated drape, iodine-impregnated adhesive biodrapes, sterile towels, and half-sheets should be used as needed to ensure a sterile field.

Supplemental fluids are important during most procedures, not just high-risk procedures. When a patient has been NPO for 3 hours (especially during morning procedures when he or she has been NPO since the night before), they are somewhat volume-depleted and more prone to vasovagal reactions. Supplemental fluids before, during, and after procedures help prevent such reactions.

In addition, having fluids already flowing, in the event the patient becomes hypotensive, is advantageous; this can also help flush medication(s) through the line. Supplemental fluids should be used cautiously if the patient is volume-sensitive, such as with congestive heart failure or renal pathology.

Supplemental oxygen should be dictated by the situation. If IV sedation is administered, supplemental oxygen should be used as needed to help maintain the patient’s oxygen saturation above 92%. If the patient has COPD or other pulmonary pathology, supplemental oxygen should be used sparingly because too much oxygen may further suppress respiratory drive.

In addition, if the patient has chronic pulmonary disease, the treating physician must confirm that they can tolerate the position required by the procedure. If necessary, obtain clearance from the patient’s pulmonologist or internist.

Patient Monitoring

Patient monitoring should minimally include blood-pressure and heart-rate monitoring. If the patient is infirm, a high-risk procedure is being performed, or IV sedation is being used, cardiac monitoring and pulse oximetry should also be employed. Baseline vital signs should be obtained before the procedure (for purposes of comparison during and after the procedure).

Preprocedure hypertension should be approached with caution. A patient with cerebrovascular disease may require a higher-than-normal blood pressure to maintain cerebral perfusion; thus, adjusting his or her blood pressure could incite a stroke. If lowering the patient’s blood pressure is medically safe and appropriate, gentle IV sedation is generally all that is required. Sublingual calcium channel blockers should be avoided. In addition, if IV sedation for the procedure is planned, blood pressure reduction with other medications should be avoided prior to sedation, as this combination of drugs could lower the blood pressure to dangerous levels.

Cardiac monitoring should be employed for any patient with a significant cardiovascular history—or when known risks of the planned procedure might place the patient at risk for cardiovascular complication. In general, cardiac monitoring should be performed for any patient with a known history of myocardial infarction or angina; for any significantly invasive procedure (e.g., spinal implant); for any intraspinal cervical or thoracic procedure; for any procedure that may place a significant volume of local anesthetic or narcotic in the spinal canal or systemic circulation; or for anyprocedure that will require a significant amount of IV sedation. A rhythm strip should be run before, during, and after the procedure and included on the patient’s chart.

Patient Recovery

The recovery of the patient following the procedure is critically important and is often ignored. The postprocedural period is when most procedure-related complications occur. Complications that can occur during the immediate postprocedure period include hypotension, vasovagal reactions, sensorimotor blockade, excessive somnolence, respiratory suppression, and cardiovascular complications arising from one or more of the aforementioned complications.

For these reasons, a medically-reasonable recovery protocol (ultimately allowing the patient to recover in a monitored situation until he or she is alert, oriented, and able to tolerate fluids and ambulate as well as expected) is important. The following abbreviated version of the protocol for routine spinal-injection procedures, with minimal or no sedation, is recommended.

The patient is allowed to remain in the procedure room in the recumbent position for 5 to 10 minutes under the observation of the nurse, while two additional sets of vital signs are taken. If the patient is in satisfactory condition, he or she is slowly moved to a sitting position and transferred to a wheel chair, or assisted with ambulation to the recovery area. The patient is observed there with intermittent vital-sign monitoring for at least 20 minutes, or until they have met the above criteria. Another person must drive the patient home if IV sedation was given during the procedure.

If the specific intervention was more significant than a simple spinal injection (e.g., spinal implant, percutaneous discectomy), the recovery period may last up to 8 hours. It may be necessary to hold the patient overnight if the previously listed criteria are not met. When they have met discharge criteria, they are discharged with appropriate safety and follow-up instructions.

General Complications of Spinal Injections

Infectious Complications

Infections, ranging from minor to severe conditions such as meningitis,^9,¹⁰ epidural abscess,¹¹^–¹³ and osteomyelitis (Figs. 6-1 and 6-2),^14,¹⁵ occur in 1% to 2% of spinal injections. Severe infections are rare and occur in from 1 in 1000 to 1 in 10,000 spinal injections. Severe infections may have far-reaching sequelae, such as sepsis, spinal-cord injury, or spreading to other sites in the body via Batson plexus or direct contiguous spreading. Poor sterile technique is the most common cause of infection. Staphylococcus aureus is the most common offending organism causing infection from skin structures.

Figure 6-1 Lumbar epidural abscess (MRI view). T2-weighted image demonstrating an epidural abscess (white arrows) severely compressing the thecal sac at C-6 and C-7 levels.

Figure 6-2 Vertebral osteomyelitis and paraspinal abscess (CT scan view). A, Note the paraspinal soft tissue mass in front of the destructive process of the L-5 vertebra. B, Soft tissue windows following intravenous contrast enhancement showing the large multilocular abscess in the soft tissues enhanced (black arrows).

Infection from gram-negative aerobes and anaerobes may occur from inadvertent intestinal penetration. Usually, discitis from lumbar discography involves a gram-negative aerobe, is self-limited, and resolves with early recognition and administration of appropriate antibiotics. Cervical discitis, however, is often life threatening, due to the aggressive gram-negative anaerobes that colonize the esophagus.

If the infection is a mild cutaneous infection and the patient is immunocompetent, it will probably resolve with local disinfection. The physician should make specific hygiene recommendations and monitor this infection expectantly. If it appears to pursue a more aggressive course but does not involve spinal structures, appropriate oral antibiotics on an outpatient basis and frequent follow-up may be all that is required.

If the infection appears to progress to spinal structures or spaces, or if the patient is infirm or otherwise predisposed to infection, in-patient evaluation and care with appropriate IV antibiotics is usually required. If epidural abscess occurs, emergent surgical drainage must be considered to avoid neural damage or other complications.¹⁶ Early detection and treatment of epidural or intrathecal infection is necessary to avoid morbidity and mortality. It usually manifests with severe back or neck pain, fever, and chills, with a leukocytosis developing on the third day following the injection.¹³

Patients with diabetes or other immunocompromised conditions are more susceptible to infection and should be followed very closely following spinal injections. With these patients, if infection is suspected or confirmed, they must be evaluated and treated aggressively.

Preexisting systemic infection is a relative contraindication to spinal injection. If the spinal injection is critical to the overall care of the patient with preexisting systemic infection, the risks and benefits must be carefully weighed before performing the injection. In addition, administering prophylactic antibiotics for 72 hours before the injection should be considered. Knowing the local standards of care for preventing or treating spinal injection-related infections and routinely reviewing current microorganism susceptibilities are important.

Cardiovascular Complications

Bleeding is a risk inherent to all injection and surgical procedures. The potential for bleeding during spinal injection is increased by liver disease, the consumption of warfarin or other anticoagulants,^5,^17,¹⁸ certain inherited anemias (such as G6PD deficiency or sickle-cell anemia), coagulopathy from any cause, and venous puncture.

The epidural vasculature is injured in 0.5% to 1% of spinal injections on average, and is more common with placement of the needle in the lateral portion of the spinal canal than the midline.¹⁹ Significant epidural bleeding may cause the development of an epidural hematoma. Clinically-significant epidural hematomas are rare, with a reported incidence of less than 1 in 4000 to 1 in 10,000 lumbar epidural cortisone injections; and may lead to irreversible neurologic compromise if not surgically decompressed within 24 hours.¹⁹^–²⁵ Retroperitoneal hematomas may occur following spinal injection if the large vessels are inadvertently penetrated. These hematomas are usually self-limited but may be a cause of acute hypovolemia or anemia. In addition to bleeding, a variety of dysrhythmias may occur. When a dysrhythmia occurs, treatment should be initiated immediately. The entire team of primary care physicians (PCPs) must be able to function synergistically when treating a dysrhythmia.

ACLS code scenarios should be run in the procedure facility no less than quarterly; all PCPs should know how to alert other staff and extended PCPs immediately; and everyone should know their specific roles in such situations. In addition, all PCPs should know where emergency care equipment is located and how to use it within the limits of their roles. Treatment of individual dysrhythmias is beyond the scope of this chapter; however, the reader is directed to the Emergency Cardiac Care Algorithms included in Appendix I and other sources for more detailed information.^26,²⁷

Neurologic Complications

Neurologic complications are rare. The most common causes of neural injury during spinal injection are: direct trauma to the spinal cord or nerve roots from a needle; compression from an epidural hematoma; or involvement by infectious exudate. Other causes include stroke from injection-, sedation- or cardiac-induced hypotension; dislodgement of plaque from intraarterial injection; or anoxia from respiratory arrest or laryngeal obstruction.

The proximity of the vertebral artery during cervical transforaminal or facet joint injections requires particular knowledge of the three-dimensional anatomy of the cervical spine, as well as specific training and expertise in cervical spinal-injection procedures, to consistently protect these structures. Injection into this vessel may cause a posterior circulation stroke, hematoma formation and occlusion of the vessel, or injection of air. Seizure may also occur if local anesthetic is injected into the vessel.

Studies demonstrate that fluoroscopically-guided spinal injections are less apt to cause inadvertent neural injury or injection into a vascular structure.²⁸ A pertinent neurologic review of symptoms and a physical examination should be performed immediately if a neurologic complication is suspected.

Respiratory Complications

Respiratory arrest occurs when a patient becomes apneic for greater than 1 minute, due to lack of central respiratory drive or paralysis of the muscles of respiration.²⁹ Respiratory arrest may occur from a variety of causes, including oversedation, central nervous system trauma, and intrathecal or epidural injection of a sufficient amount of local anesthetic to cause spinal anesthesia.

Treatment requires immediate recognition of the condition and emergent support of vital signs. If the cause is self-limited, treatment may require the support of respiration and other vital signs as needed until spontaneous and adequate respiration resumes. If the cause can be easily reversed, it should be (as when too much narcotic or sedative has been given). In this particular situation, it is important to remember the half-life of the reversing agent, compared to the half-life of the narcotic or sedative being reversed. If the narcotic or sedative’s half-life is longer than that of the reversing agent, respiratory compromise may resume when the reversing agent has been metabolized.

The true incidence of respiratory depression due to spinal opioid administration is unknown. Factors that may cause respiratory depression include the use of sedatives, parenteral or spinal opioids, and local anesthetics. One of the main advantages of spinal versus parenteral opioid administration is the lack of respiratory depression with the former.³⁰ It should be emphasized that respiratory rate alone is inadequate to establish the presence or lack of respiratory depression. The measurement of blood gases remains the preferred option.²⁹

Other respiratory complications due to spinal injections include pneumothorax and injury to the recurrent laryngeal nerve. A pneumothorax may occur during a lower cervical procedure such as a discogram, selective nerve root block, or thoracic procedure (such as an intercostal nerve block). As a general rule, a pneumothorax may not occur if a needle penetrates the pleural cavity or lung parenchyma, unless it is placed through a bleb, the needle is 18-gauge or larger, or a solution has been injected.

When a pneumothorax does occur, it is usually self-limited and causes only minor collapse(s) of the lung (10%).³¹ Treatment includes close observation with supportive care, usually in a hospital, and serial chest radiographs. A chest tube should be placed if the pneumothorax advances significantly over 25% or the patient develops shortness of breath or other signs of respiratory distress.

Injury to the recurrent laryngeal nerve may cause unilateral vocal-cord paralysis, reduced ability to protect the airway, and hoarseness. This injury is usually self-limited and resolves on its own; but it may be clinically significant while the patient is recovering from sedation, or when there is preexisting underlying pathology that causes marginal airway protection (e.g., stroke or laryngeal cancer).

Urological Complications

The application of local anesthetics and/or opioids to the lumbar and sacral nerve roots results in higher incidence of urinary retention.³² This side-effect of lumbar epidural nerve block is seen more commonly in elderly males, multiparous females, and patients who have undergone inguinal and perineal surgery. Overflow incontinence may occur if such a patient is unable to void or bladder catheterization is not utilized. All patients undergoing lumbar epidural nerve block should demonstrate the ability to void the bladder prior to discharge from the pain center.

Dural Puncture

In the hands of the experienced interventional spine specialist, inadvertent dural puncture during lumbar epidural injections should occur in <0.5% of cases (or 1 in 200 epidural injections).³³ This occurs when the dura mater is violated by the epidural needle, and a sufficient amount of cerebrospinal fluid leaks out from the thecal sac, causing a positional headache.³⁴^–³⁷ The rare occurrence of postdural puncture (spinal-tap) headache is an annoying side effect, but is generally benign for the most part and will pass without permanent harm or morbidity to the patient.

Rarely, with dehydration and severe nausea and vomiting, uncal herniation may occur, with associated brainstem involvement and potentially death.³⁸ If a needle is placed subdurally and epidural doses of local anesthetics are administered, the signs and symptoms are similar to subarachnoid injection.³⁹ The subdural or subarachnoid injection of large doses of local anesthetics may cause total spinal anesthesia, loss of consciousness, hypotension, cardiovascular arrest, apnea, and even death. This condition requires immediate resuscitative measures and support of all vital signs until the condition resolves. Intubation is usually required to adequately control the airway and ventilate the patient.

Fluoroscopic Exposure

Epidural injections performed without fluoroscopy are not always placed into the epidural space, at the desired vertebral interspace; or the medication does not get to the desired target organ due to anatomic abnormality, as noted in various sources.⁴⁰^–⁴⁸ For this reason, most spine-management specialists recommend fluoroscopic direction and the use of nonionic or low ionic contrast agents for epidural injections. This helps confirm accurate needle placement and the delivery of the injected solution to the appropriate target organ.⁴⁸

The risk of fluoroscopic exposure to the patient is minimal, for one procedure or several isolated ones because each procedure should require minimal (<20 seconds) fluoroscopic exposure time. Related exposure to the physician, attending nurse, x-ray technician, and anyone else consistently in the procedure room should be viewed as cumulative.

To limit exposure to these patient care providers (PCPs), it is important to note that radiation dissipates at the inverse of the square of the distance from the tube. As a result, if PCPs are able to stand six feet or more away from the fluoroscopic tube, their risk of excessive exposure is minimal. The fluoroscopy anode should also be kept under the procedure table because this anode is the source of the radiation. With these precautions, the patient absorbs the bulk of the directed radiation. The vast majority of the relatively small amount of other radiation spilled into the room is known as “scatter radiation”, which has much less ability to penetrate tissues than directed radiation.

In addition, the PCPs should wear appropriate protective garments. The physician should wear a lead apron, thyroid shield, radiation-attenuating gloves, and perhaps lead-lined glasses. The nurse and x-ray technician should wear wrap-around lead aprons because their backs are frequently turned toward the radiation source, and thyroid shields. All PCPs should wear radiation badges on their thyroid shields and aprons; and the physician should consider wearing a ring badge, if his or her hand is routinely in the radiation field during active fluoroscopy.

Finally, the fluoroscopy unit must be routinely maintained and inspected to confirm its proper function and safety. Proper fluoroscopy use (including safe radiation practices) can direct and confirm accurate needle placement, maximizing benefits while limiting potential risks for patients and PCPs.

Medication Reactions

Adverse drug reactions are rarely seen with medications used during spinal injections. The treating physician should be aware of drug toxicity, side effects, allergic reactions, and concentration and dosing of all medicines used.

Lidocaine and bupivacaine are the most common local anesthetics used during spinal injections. Awareness of their potential central nervous system (CNS) effects, cardiovascular toxicity, and side effects is very important. Strict cardiovascular and neurologic monitoring is required before, during, and after the procedure. Although most anaphylactic reactions typically occur within 2 hours after the epidural injection, they have been known to occur up to 6 hours later.⁴⁹

Local anesthetics primarily function by reversibly blocking sodium channels in nerve and muscle membranes, having a direct effect on sympathetic nerves when injected into the subarachnoid space and the cardiac tissue (when injected intravascularly). If the sympathetic system is sufficiently blocked, hypotension may result; and if cardiac muscle is sufficiently blocked, decreased contractility may result.

When injected intravenously, lidocaine is “fast-in and fast-out,” reaching steady state in one to two heart beats. Bupivacaine is “fast-in and slow-out,” and its blocking action increases as the heart works harder. These are the main direct effects that can cause cardiac arrest. Cervical and thoracic level blocks have an increased risk for complications because of the regional neural supply to the heart and respiratory control.

Central nervous-system toxicity by 1% lidocaine has an onset at plasma concentrations of 5-10 mcg/mL, which is slightly more than 400 mg (or 40 mL) of total intravenous bolus. Bupivacaine is about four times more toxic than lidocaine, with a toxic bolus of 100 mg (or 10 mL).⁵⁰

A person with CNS toxicity usually presents with complaints of circumoral numbness, disorientation, lightheadedness, nystagmus, tinnitus, and/or muscle twitching in the face or distal extremities. Peak plasma concentrations occur 10 to 20 minutes after injection. For that reason, patient monitoring for at least 30 minutes following an epidural injection with a significant bolus of lidocaine or bupivacaine is mandatory.

Methylprednisolone, triamcinolone, and betamethasone are the most commonly used corticosteroid preparations. Side effects are uncommon but could include headache, dizziness, insomnia, facial erythema, rash and pruritus, low-grade “fever” (<100° F), hyperglycemia, transient hypotension and hypertension, increased back or limb pain, fluid retention, mood swing, euphoria, menstrual irregularity, and gastritis.¹⁷ Other rare side effects include elevation of cerebrospinal-fluid protein levels, septic or aseptic meningitis, worsening of multiple sclerosis symptoms, sclerosing spinal pachymeningitis, exacerbation of latent infection, near-fatal septic meningitis (intrathecal injection), hypercorticism, and congestive heart failure.

Anaphylactic and Allergy Reactions

Anaphylactoid (without histologic immune response) and anaphylaxis (with a histologic immune response) occur most often within 2 hours after the epidural injection, and have been known to develop up to 6 hours later.⁴⁹ These usually cause fatalities by respiratory-related complications involving mechanical airway obstruction. Therefore, monitoring patients closely for approximately 30 minutes after the procedure is recommended. Informing the patient about possible risks and side effects can also expedite early identification of complications.

Bleeding Complications

Epidural hematoma formation following injection is extremely rare. Bleeding usually occurs because of damage to the veins in the highly vascular epidural space. Medications that interfere with the clotting mechanism include heparin, warfarin, aspirin, and most nonsteroidal anti-inflammatory drugs (NSAIDs).^5,^17,¹⁸

Patients usually present with severe neck or back pain, associated with any significant neurologic complaint, right after the procedure.¹⁷ An immediate physical examination, followed by a computer tomography (CT) scan or MRI (magnetic resonance imaging) scan, is essential for patients thought to have an epidural hematoma because early surgical intervention can limit or even prevent permanent neurologic damage (Fig. 6-3).

Figure 6-3 Acute epidural hematoma and subarachnoid hemorrhage (CT scan view). Thoracic spine view showing a lenticular, high-density epidural hematoma (open arrow) causing spinal cord compression. Acute hemorrhage is noted in the subarachnoid space.

Specific Complications of Selective Spinal Injections

Lumbar Epidural Injections

The lumbar epidural space is highly vascular. Inadvertent intravenous placement of the epidural needle occurs in approximately 0.5% to 1% of patients undergoing lumbar epidural anesthesia.³³ This rare complication is mostly seen with distended epidural veins, such as those present in pregnant patients and patients with large abdominal tumor masses.

If the misplacement is unrecognized, injection of a large volume of local anesthetic directly into an epidural vein may result in significant local anesthetic toxicity.⁵¹ Careful four-quadrant aspiration (aspiration in all four quadrants by rotating the needle), prior to injection of drugs into the epidural space, is mandatory in identifying the vascular placement of the needle when performing a “blind” (nonfluoroscopically-guided) epidural injection.

Neurologic complications of lumbar nerve block are uncommon if proper technique is used. Usually, these complications are associated with a preexisting neurologic lesion or with surgical or obstetric trauma, rather than with the lumbar block itself.³²

Direct trauma to the spinal cord or nerve roots is usually accompanied by pain. Any significant pain that occurs during placement of the epidural needle or catheter, or during injection, should warn the injectionist to pause and confirm needle placement before proceeding.³³ The use of deep intravenous sedation or general anesthesia prior to initiation of epidural nerve block may reduce the patient’s ability to provide accurate verbal feedback if needle misplacement occurs. Therefore, conscious sedation or general anesthesia prior to epidural nerve block should be employed with caution.⁵²

When the patient’s lower-extremity neurologic status deteriorates rapidly or when a cauda equina syndrome is suspected within 24 to 48 hours following an epidural procedure, an expanding epidural hematoma should be considered.⁵³ If the injectionist suspects that diagnosis, an immediate and complete clinical evaluation is mandatory. If the diagnosis is still suspected following the clinical evaluation, a lumbar CT scan or MRI scan should be obtained (Figs. 6-4 through 6-6). If the diagnosis is confirmed, an emergent surgical consult to consider decompression should be arranged.

Figure 6-4 Herniated nucleus pulposus (MRI view). A, T1-weighted sagittal image showing impingement of the thecal sac by the herniated nuclear material (white arrow). B, Axial sagittal gradient echo image showing the herniation shifted to the left (black arrow).

Figure 6-5 Posterolateral disc herniation (CT scan view). Left-sided focal protrusion of the disc (black arrow), leading to posterior displacement of the left S1 nerve root (open arrow) and effacement of the anterior epidural fat. This is in contrast to the epidural fat on the right and normal location of the right S1 nerve root (white arrow).

Figure 6-6 Posterolateral disc herniation (lumbar myelogram view). Oblique view performed with water-soluble contrast revealing the abrupt termination and widening of the S1 nerve root sleeve (white arrow).

Caudal Epidural Injections

Incorrect needle placement during caudal epidural injection occurs 25% to 40% of the time.^54,⁵⁵ The needle may be placed outside the sacral canal, resulting in injection of air or fluid into the subcutaneous tissues, periosteum, sacrococcygeal ligament, sacral marrow cavity, and/or pelvic cavity, possibly entering both the rectum and/or vaginal vault.

The application of local anesthetic and opioids to the sacral nerve roots results in increased incidence of urinary retention, especially in elderly males and multiparous females, and after inguinal and perineal surgery. The use of smaller doses of local anesthetic will help avoid these burdensome complications, without adversely affecting the efficacy of caudal epidural steroid injections when treating painful conditions.⁵⁶

Because of the proximity of the sacral hiatus to the perineum, there is increased incidence of epidural abscess and meningitis compared to the interlaminar or transforaminal injection route. When placing the epidural needle, remembering that the thecal sac usually ends at the S2 bony level, but may end as low as S4, is important. Therefore, the needle should be placed no higher than absolutely necessary to assure epidural injection.

If the needle penetrates the thecal sac, results may include a positional headache and/or lowering of the body’s protection against meningitis because the thecal sac will have been violated. In addition, if this needle malposition is not detected prior to injection, an intrathecal injection may occur—potentially causing a spinal block and its associated sequelae.

Cervical Epidural Injections

Because of the potential for hematogenous spread via Batson plexus, local infection and sepsis represent absolute contraindications to the cervical approach to the epidural space. Anticoagulation and coagulopathy also represent absolute contraindications to cervical epidural nerve block because of the risk of epidural hematoma.^5,^6,^17,¹⁸

Because the spinal cord lies within the spinal canal, there is increased risk for spinal cord injury with the injection technique, as compared to lower- or midlumbar injections. Central canal stenosis, either from bony eburnation, central disc herniation, or congenital shortening of the pedicles, represents an absolute contraindication to performing an interlaminar epidural injection at that level (Figs. 6-7 and 6-8).^57,⁵⁸

Figure 6-7 Degenerative central spinal stenosis (schematic view). Lumbar vertebra at the disc level is noted in the axial view. It is noted that the osteophytes derived from the articular processes can lead to thecal sac compression.

Figure 6-8 Central spinal stenosis (CT scan view). Marked hypertrophy of the ligamentum flavum (open arrows) is noted to directly cause thecal sac compression; also seen is mild annular bulging and facet joint arthropathy.

Thoracic Epidural Injections

Thoracic epidural techniques are similar to lumbar techniques; but the presence of the narrow epidural space, and proximity to the spinal cord in the thoracic vertebral canal, makes spinal cord trauma more likely. The incidence of spinal cord damage is unknown, although the incidence of infection is increased in the thoracic spine when compared to the lumbar spine.⁵⁹

The presence of the lungs on either side of the spine makes a pneumothorax a potential complication not usually considered with either a cervical or lumbar injection. The injection of local anesthetic in the mid-thoracic epidural space may cause inhibition of the cardiac accelerator zone, causing hypotension and bradycardia and its potential sequelae. In addition, a thoracic motor block from either the epidural or intrathecal injection of local anesthetic can cause up to 50% reduction in tidal volume, making adequate ventilation of a patient with pulmonary disease difficult.

Selective Nerve Root Blocks

Selective nerve root blockade has been used interchangeably as a spinal nerve block, selective epidural, or an anterior ramus block.⁴⁸ In this brief discussion we will deal with each separately.

A spinal nerve block occurs when the needle tip is placed within the neural foramen; and local anesthetic affects only the spinal nerve and does not migrate inside the spinal canal. The main risk of this injection technique is trauma to the spinal nerve or dorsal root ganglion. If the needle penetrates the dural sleeve, an intrathecal injection may occur with associated risks and complications.

A selective epidural occurs when fluid is injected into the epidural space via a neural foramen. To accomplish this, the needle is also placed within the neural foramen; thus, trauma to the spinal nerve or dorsal root ganglion is possible. Injection into the dural sleeve is also possible—with all its associated risks and complications.

An anterior ramus block is an extraspinal injection of the anterior ramus. This occurs 1 to 2 cm outside of the neural foramen and local anesthetic does not reach the spinal canal or spinal nerve. The main complication of this blockade is direct trauma to the anterior ramus from the needle or the disruption of the neural vasculature, causing an intraparenchymal hematoma or neural infarct.

Discography

The most common severe complication after discography is infection of the disc, commonly referred to as discitis. This should occur no more frequently than in 1 in 500 to 1 in 750 discs injected.^60,⁶¹ The most common organisms infecting the lumbar disc are S. aureus and Staphylococcus epidermidis.^60,⁶²

Occasionally, a colonic organism involves the lumbar discs, resulting from penetration of the colon with the discography needle. Because of the limited blood supply of the disc, such infections may prove difficult to eradicate.

Discitis usually manifests as an increase in spine pain 5 to 14 days following discography. Acutely, there should be no change in the patient’s neurologic status. An elevated sedimentation rate will be seen within the first week to 10 days.⁶³^–⁶⁵ The preferred option in the detection of discitis is now considered to be magnetic resonance imaging (MRI), which was found to be superior to bone scanning with a 92% sensitivity, 97% specificity, and 95% overall accuracy (Fig. 6-9).⁶⁶^–⁶⁸

Figure 6-9 Lumbar disc space infection (MRI view). T1-weighted image showing areas of low signal of the L-4 and L-5, with the anterior paraspinal mass noted (white arrow).

The incidence of thoracic discitis following a thoracic discogram is unknown, but the organisms infecting those discs following discography should be similar to those involving the lumbar discs. Similarly, the incidence of pneumothorax and large-vessel damage following thoracic discography is also unknown. In one series of 230 outpatient thoracic discograms, Schellhas reported a zero incidence of pneumothorax.⁶⁹ Although this is encouraging, the complication does still occur; thus, the procedure should not be attempted without substantial experience and training.

Cervical discitis is generally profound and life threatening. The esophagus has gram-negative and anaerobic bacteria as components of its normal flora. Therefore, placing the discography needle through it and into the disc may seed the disc with bacteria that may initiate a profound infection.

In the mid- and lower-cervical spine, the esophagus lies on the left side of the larynx. The carotid sheath lies on the anterolateral surface of the cervical spinal column. As a result, a cervical discogram should be performed using a right-sided paralaryngeal approach. In performing this approach, the esophagus should be pushed to the left and the carotid sheath to the right, thereby minimizing the risk of trauma to these structures. If the needle does penetrate the carotid sheath, direct injury to the vagus nerve or carotid artery could occur with associated risks and complications.

In addition to infectious complications, pneumothorax may occur after cervical and thoracic discography. This complication should rarely occur if appropriate techniques are used. Most pneumothoraces following cervical or thoracic discography are small (10% to 15% of lung volume) and can often be treated conservatively. However, all pneumothoraces must be taken seriously and observed overnight, with serial chest radiographs and close monitoring of vital signs and blood gases. If the pneumothorax progresses, a chest tube must be placed.

Direct trauma to the nerve roots and the spinal cord can occur if the needle is allowed to traverse the entire disc or is placed too laterally. These complications should rarely occur if appropriate techniques and precautions are used. Such needle-induced trauma to the cervical spinal cord can result in syrinx formation with attendant progressive neurologic deficit, including quadriplegia.

Intercostal Nerve Blocks

Given the proximity of the pleural space, pneumothorax after intercostal nerve blocks is a distinct possibility. The incidence of the complication is less than 1% (0.082%),⁷⁰ but it occurs with greater frequency in patients with chronic obstructive pulmonary disease. Because of the proximity to the intercostal nerve and artery, when analgesia is produced from the intercostal block, the compensatory vasoconstriction eases, and the patient may become hypotensive. In a similar manner, intercostal blocks can lead to respiratory failure when pain relief from the block unmasks the ventilatory depression of previously administered, but ineffective, parenteral narcotics.⁷¹

Facet Joint Nerve Blocks

The problem cited most often with these procedures is a transient exacerbation in pain (about 2% incidence), lasting as long as 6 weeks to 8 months in some cases.^17,^72,⁷³ Spinal anesthesia may occur after facet joint injection if the needle is positioned within the thecal sac, or if there is an abnormal communication between the facet joint capsule and the thecal sac. Chemical meningitis after lumbar facet block has been reported.⁷³^–⁷⁵ These complications are thought to have occurred after inadvertent dural puncture. Facet-capsule rupture also occurs, especially if more than 2.0 mL of injectate is used for intraarticular injections.⁴⁸

During performance of cervical facet blockade, there is potential risk of entry into the intervertebral foramen, spinal canal, and vertebral artery. These complications occur more frequently using a lateral intraarticular technique than with blockade of the medial branches innervating the cervical facets because the former technique requires deeper penetration of the needle into the joint and toward the spinal structures. Local anesthetic may leak out of the joint into these areas, causing motor and sensory blockade with attendant risks and complications.

Third occipital nerve blocks can cause transient ataxia and unsteadiness due to partial blockade of the upper cervical proprioceptive afferents and the righting response.^76,⁷⁷ In one study of cervical facet joint radiofrequency denervation, 13% of patients complained of postprocedure pain that resolved in 2 to 6 weeks. Four percent of patients complained of occipital hypesthesia, probably due to a lesion of the third occipital nerve, which resolved in 3 months.⁷⁷ No persistent motor or sensory deficits occurred.