Sympathetic Nerve Block

Anatomy and Physiology

Central sympathetic nuclei are located in the intermediolateral nucleus of the lateral grey column of the spinal cord, extending from T1 to L2–L3 levels. Their axons leave the spinal cord in the ventral roots and form white rami shortly after the ventral ramus separates from the spinal nerve. These myelinated white rami then proceed to either paravertebral or prevertebral ganglia. Paravertebral ganglia form the sympathetic trunk along both sides of the vertebral column, consisting of 20 to 24 paired and interconnected ganglionic nodes that join together at the coccygeal level to form the terminal unpaired node of the sympathetic chain known as the ganglion Impar. Prevertebral (preaortic) ganglia are organized in plexuses surrounding major branches of the abdominal aorta (the celiac, superior mesenteric, and inferior mesenteric ganglia). Preganglionic white rami reach these ganglia after transiting through the paravertebral ganglia and abdominopelvic splanchnic nerves.

The postganglionic fibers leave the ganglia in the form of unmyelinated grey rami and either join somatic nerves or form visceral nerves (they course along with the corresponding visceral vascular bundles or join splanchnic nerves). The afferent input to sympathetic ganglia is relayed via general visceral afferent fibers that carry pain and reflex sensations from internal organs to the dorsal horn of the spinal cord.[6][7]

From sensory receptors located in the organ of origin, this input follows a pathway to the corresponding sympathetic ganglion and into a mixed spinal nerve along with white rami on a course to the dorsal root ganglion (DRG), where the cell body of the general visceral afferent nerve is located. Such anatomical peculiarities and a distinct spatial separation of sympathetic and somatic nerve structures (particularly on cervical, lumbar, and sacral levels) allow for selective interventional blockade of sympathetic structures that relay visceral nociceptive information to control autonomic function.

Sympathetic blockade with local anesthetics is used diagnostically to evaluate if the pain is sympathetically mediated. Often, pain relief lasts longer than the expected action of local anesthetic, making the block therapeutic. Adding a depot corticosteroid, if indicated, can additionally prolong the action of the sympathetic blockade from days to weeks. Once the block is proven effective, the use of chemical neurolysis or ablative modalities may provide a longer-lasting effect. When correct needle placement is confirmed radiographically, and significant analgesia is achieved using a very low concentration of local anesthetic—without signs of sensory or motor blockade—it is presumed the effects occurred due to the sympathetic block.[8] However, larger volumes of anesthetic are more likely to spread to somatic nerves near ganglia and result in sensory fiber block, potentially creating a false-positive outcome.

Indications

Diagnostic sympathetic blocks are used to confirm the presence of sympathetically mediated pain. Longer-acting therapeutic blocks can be performed by injecting neurolytic substances or repeated local anesthetic administrations. Physical modalities, such as radiofrequency denervation or cryo-neurolysis of sympathetic nerves, may be utilized.

Sympathetic blocks are used to treat visceral, vascular, and neuropathic pain.

Visceral Pain

Foregut and midgut structures (stomach, duodenum, pancreas, biliary system, liver, small intestine) are innervated by the celiac plexus. Blocking this plexus may relieve pain and nausea, often associated with malignancies of the organs, as mentioned above. If successful, this procedure may significantly reduce or even eliminate the need for opioid therapy. The relief may last weeks to months if a neurolytic agent is used.[9] Celiac plexus blocks and neurolysis may be repeated if symptoms recur, though the duration of pain relief may diminish with repeated neurolysis.[10]

Hindgut structures (descending, sigmoid colon, and proximal rectum) and pelvic organs (uterus, ovaries, prostate, urinary bladder, testes, and seminal vesicles) are innervated by the superior hypogastric plexus. A blockade of this prevertebral ganglion may be used to treat persistent or intractable pelvic and rectal pain that failed conservative treatment measures.[11]

Inferior hypogastric plexus block may treat pelvic, perineal, and genital pain of benign or malignant etiology. This procedure is not commonly used due to the pre-sacral location of the ganglion, posing difficulty to access and a higher risk of complications.[12]

Distal structures of the pelvis are innervated sympathetically by the ganglion Impar. This ganglion may be blocked to treat malignant vulvar, rectal, and anal pain, intractable sacral and perineal pain (eg, postherpetic neuralgia), or coccydynia.[13]

The thoracic paravertebral sympathetic chain transmits nociceptive input from the thoracic viscera and acts as a relay station for white rami traveling to the cervical, abdominal, lumbar, and sacrococcygeal sympathetic nodes. Due to proximity to somatic nerves and complex surrounding anatomy, the thoracic paravertebral sympathetic chain is rarely blocked, as the effect is often difficult to predict. Furthermore, the anatomy poses a higher risk of a somatic block and other complications.[14]

If the primary disease process involves somatic structures (eg, malignancy invading abdominal walls or musculoskeletal tissues, nerves), and the pain gains a somatic component, a sympathetic block may be less efficacious. In such cases, regional and neuraxial techniques may improve the quality of pain relief. Neuraxial analgesia (intrathecal or epidural) will block somatic and visceral afferents simultaneously, which is the basis for the implantation of long-term intrathecal drug delivery systems.

Neuropathic Pain

Sympathetic blocks can provide significant yet often incomplete relief of neuropathic pain and are usually combined with adjuvant therapies (eg, physiotherapy, medications, and neuromodulation). The role of sympathetic blocks in treating acute herpes zoster pain remains unclear. Pain from herpes zoster of the trigeminal region may be treated with stellate ganglion blocks, which may decrease the risk of developing postherpetic neuralgia.[15][16]

Allodynia and pain from herpes zoster of the trunk and extremities may be relieved better with epidural or paravertebral injections with local anesthetics and corticosteroids.[17][18][19] The efficacy of sympathetic blocks for the treatment of postherpetic neuralgia remains controversial.[20][21] Only one case report suggests lumbar sympathetic block may be efficacious in treating refractory painful diabetic neuropathy.[22] 

Phantom limb pain is hypothesized to be partially sympathetically mediated and pathophysiologically similar to complex regional pain syndrome type II. A recent case series and pilot study suggest the effectiveness of sympathetic blocks in providing stump pain relief. Yet, the role of sympathetic blocks in phantom limb pain remains unclear due to limited evidence.[23][24] 

Ultimately, sympathetic nerve blocks are not indicated for chronic treatment of neuropathic pain unrelated to CRPS according to the practice guidelines from the American Society of Anesthesiologists Task Force of Chronic Pain Management and the American Society of Regional Anesthesia and Pain Medicine(ASRA).[25]

The sympathetic blockade has proven beneficial in treating complex regional pain syndrome (CRPS). In part, the pathogenesis of CRPS stems from the emerging hypersensitivity of nociceptors to norepinephrine released from sympathetic efferents and the loss of the SNS’s inhibitory influence on pain.[26] Such sympathetically maintained pain is present in one-third of patients with CRPS.[27]

In this condition, the effects of diagnostic sympathetic blockade may be prolonged and therapeutic, aiding in the rehabilitation of patients. Both stellate ganglion (for upper extremity CRPS) and lumbar sympathetic blocks (for lower extremity CRPS) with local anesthetics and adjuvants (eg, clonidine and steroids) offer benefit and are indicated when conservative, noninvasive treatments fail.[28]

Neurolysis or ablation of the lumbar plexus may provide longer-lasting relief in patients with short-lived but adequate relief from sympathetic blocks.[29]

Vascular Pain

Pain from tissue ischemia (eg, vasospastic, thrombotic, or embolic) is transmitted via sympathetic afferent fibers and is enhanced by sympathetic vasoconstriction. Simultaneously, chronic ischemia can directly damage soft tissues (eg, ulceration) and nerves, adding somatic and neuropathic nociceptive components, respectively. Lumbar sympathetic block for treating resting pain of obliterative lower extremity disease (eg, thromboangiitis obliterans and atherosclerosis) was historically among the most beneficial neural percutaneous interventions available. Most patients responded with significantly decreased pain and increased perfusion in the affected extremity.[30]

Neural ablation or denervation of the lumbar chain in these patients facilitates exercise and rehabilitation, leading to lasting improvement. Pain from chronic vasospastic disease (eg, Raynaud syndrome, acrocyanosis, livedo reticularis, sequelae of poliomyelitis, and spinal cord injury) and cold injury are quite responsive to sympathetic blocks as well.[31][32]

Hyperhidrosis

Sympathetic ganglion blocks can provide temporary relief from hyperhidrosis.[33] Surgical ganglionectomy was widely used to treat this condition; however, due to a high incidence of post-sympathectomy pain (11%)[34], this surgery is not employed. Chemical block and, if possible, lysis/ablation provide a safer alternative.

Acute Treatment of Electrical Storm

A severe form of recurrent sustained ventricular tachycardia with greater than or equal to 3 episodes in 24 hours is called an electrical storm. It is associated with a 2- to 8-fold increased risk of sudden cardiac death. A recent prospective study and several case studies reported up to 90% efficiency of left-sided or bilateral stellate ganglion blocks in decreasing ventricular arrhythmia burden.[35]

Posttraumatic Stress Disorder (PTSD) Treatment

A recent randomized control trial showed the efficacy of stellate ganglion blocks in treating PTSD.[36] It is hypothesized that the right-sided stellate ganglion blockade may locally decrease the nerve growth factor level, leading to a reduction or even reversal of the sympathetic nerve sprouting in the plexus and among its anatomic connections. This, in turn, results in the reduction of cerebral norepinephrine levels. The block also directly interrupts signaling from the stellate ganglion to the amygdala, the brain region responsible for processing emotions such as anxiety and fear. Both of these actions reduce the symptoms of PTSD, with the effect lasting from weeks to months.[37][38]

Evidence of Blockade

Common subjective signs of sympathectomy include pain relief, warmth, decrease in perspiration, and change in color of the area supplied by the nerves blocked. Objective tests are recommended and include measuring skin temperature (expected to elevate for the ipsilateral limb compared to the contralateral limb) and blood flow, skin conductance, and provocative sweat tests (eg, cobalt blue or ninhydrin sweat tests).[39][40]

Horner triad (ipsilateral partial ptosis, myosis, and facial anhydrosis) is a sign of sympathectomy at the inferior cervical (stellate) ganglion level. Yet, it does not always correlate with adequate pain relief of the upper extremity. Note that the upper extremity receives some of its sympathetic efferents from the upper thoracic ganglia, which the anesthetic from the stellate ganglion block may not reach.

Contraindications

The known allergy to medications planned to be used and refusal or inability to cooperate and consent are absolute contraindications.

Infection or malignancy with loci along the needle path is a relative contraindication due to the risk of dissemination. Anticoagulation and coagulopathy diagnoses should be addressed and treated according to ASRA guidelines before a sympathetic block, considering the proximity of the sympathetic ganglia to major vascular structures. Preexisting motor and sensory deficits, concordant with the area of the block, should be thoroughly documented, and the possibility of delaying the block until improvement of symptoms, if feasible, should be discussed.

Patients on antihypertensive medications of any class, especially those on diuretics, may develop more severe hypotension than those without hypertension. Visual alterations after stellate ganglion block have been described; thus, the availability of an escort postprocedure is essential. Bowel peristalsis may increase after celiac block, an important consideration for patients predisposed to bowel obstruction.

Equipment

Sympathetic blocks invariably shift the autonomic nervous system balance in the anesthetized nerve distribution, resulting in various potentially dangerous physiologic effects. Patients undergoing these procedures should be appropriately monitored as recommended by the American Society of Anesthesiologists (ASA) basic monitoring standards (oxygenation, ventilation, circulation).

Intravenous access and availability of crystalloid solutions for infusion are strongly encouraged if hypotension is anticipated.

Imaging studies must be reviewed before any block to evaluate the presence of altered anatomy. Depending on the image guidance technique used, a mobile C-arm X-ray image intensifier, ultrasound machine, computed tomography (CT), or magnetic resonance imaging (MRI) scanner may be used.

Additionally, an appropriately sized spinal needle(s) and syringes, blunt tip drawing needles, needles for skin infiltration, mask, bouffant, sterile gloves and drapes, topical antiseptics, contrast solution, and medications (local anesthetic, neurolytic, and adjuvant medications) will be needed.

Personnel

Procedures are performed by a trained physician with a thorough knowledge of possible complications and treatment protocols. A nurse should be present to assist throughout the procedure. If imaging (eg, fluoroscopy, CT, or MRI) is being used, a technician or other personnel to operate imaging machinery must be present. 

Technique or Treatment

Stellate Ganglion Block

Specific Indications

•  Sympathetically maintained pain of upper extremities and upper thoracic area (including CRPS types I and II)
•  Post-radiation neuritis
•  Vasospastic conditions (Raynaud syndrome) and vascular insufficiency, vasculitis, arterial embolism of the face or upper extremities
•  Pain from acute herpes zoster of upper extremities and neck
•  Posttraumatic stress disorder
•  Acute treatment of electrical storm (sustained ventricular tachyarrhythmias)
•  Hyperhidrosis [41][42]

Technique

The stellate ganglion is formed by the fusion of the inferior cervical ganglion with the first thoracic ganglion bilaterally in about 80% of the population. However, if they are not connected, the first thoracic ganglion is considered the stellate ganglion. The stellate ganglion is located anterior to the C7 transverse process and the base of the first rib on the anterior aspect of the longus colli muscle under the prevertebral fascia, posterior to the vertebral vessels, lateral to the trachea, and medial to the jugular vein and common carotid artery.

Despite its location at the level of C7, the stellate ganglion block is typically performed at the level of C6 because there is a lower risk of pneumothorax and vertebral artery puncture (note that C6 is the most inferior level at which the vertebral artery lies within the transverse foramen, whereas the vertebral artery lies anterior to the C7 transverse foramen).

The stellate ganglion block may be performed using an anterior, posterior, or vertebral body approach.[43][44] Using the anterior approach, the patient is positioned supine, with the neck slightly extended. Patients should be monitored with pulse oximetry, continuous electrocardiogram (ECG)/telemetry, and blood pressure manometry throughout the procedure. This block may be performed using landmarks, ultrasound, or CT guidance; however, it is most commonly performed under fluoroscopic guidance.

To perform this block under fluoroscopic guidance, an anteroposterior (AP) view of the cervical spine is obtained, and the C6 vertebral body is located. The carotid artery should be identified by either palpation or ultrasound and may be retracted laterally to avoid puncture during needle placement. The needle is then advanced to target the Chassaignac tubercle (anterior tubercle of the C6 transverse process) until contact with bone occurs. Then, the needle should be withdrawn very slightly (1 to 2 mm) to lie just anterior to the longus colli muscle. After negative aspiration, 1 to 2 mL of contrast is injected to visualize the appropriate spread superior and inferior to the injection site. Given negative aspiration and test dose (0.5 mL of a local anesthetic), 3 to 10 mL of local anesthetic with or without corticosteroid is injected in the area of the ganglion.

Complications and Adverse Effects

The stellate ganglion block is considered a reasonably safe procedure using the anatomical landmarks technique. Ipsilateral Horner syndrome, impaired vision, and stuffy nose are very common. Given the proximity to many vascular structures, there is also always a risk of local anesthetic systemic toxicity, damage to any surrounding vessels, bleeding, and hematoma. Vascular air embolism, pneumocephalus, perforation of trachea/esophagus, chylothorax, or pneumothorax are rare yet possible.

Wulf and Maier described a severe complication rate of 1.7 for every 1,000 blocks.[45] A systematic review by Goel et al. grouped 67 studies conducted from 1990 to 2018, reporting 260 adverse event cases. Image guidance was performed in 51.5% of these cases; 24.6% versus 26.9% of complications were reported using ultrasound or fluoroscopy guidance, respectively. Most reported adverse effects were systemic or medication-related (68.5%), versus local or procedure-related adverse effects (31.5%). The most common systemic effects were:

• Hoarseness (28%)
• Lightheadedness (7.6%)
• Hypertension (5%)
• Brachial plexus block (4.6%)
• Dysphagia (4.2%)
• Cough (2.6%)
• Intrathecal block (1.9%)
• Seizures (1.9%) due to injection in the vertebral artery
• Transient locked-in syndrome (1.5%)
• Dyspnea and respiratory depression (1.5%)
• Migraine, headache, contralateral Horner syndrome, bilateral Horner syndrome, visual hallucination, myoclonus, and allergic reaction were reported with less than 1% occurrence.
• Local complications were hematoma of surrounding neck structures (15.7%), blood aspiration (7.6%), intrathoracic bleeding (2.6%), pneumothorax, infection, and bradycardia (1.1%).
• Dural puncture, transient neurological injury, hemomediastinum, sinus arrest due to vasovagal reflex, and asystolic cardiac arrest were reported with less than 1% occurrence.[46]

Splanchnic Nerve Block

Specific Indication

Upper abdominal and retroperitoneal pain secondary to malignancy (tumors of the lower third of the esophagus, stomach, duodenal, pancreatic cancer, and biliary tract cancer). A splanchnic nerve block is used as an alternative to celiac plexus block in situations where there is pre-aortic adenopathy, significant scarring, or tumor burden in the area of celiac trunk origin, posing a risk or difficulty of guiding the needle to the celiac plexus.[47] The procedure may also be considered if the original celiac plexus block was unsuccessful. Being performed intimately close to the pleural cavity and somatic nerve roots, it carries a higher risk of pneumothorax and collateral bodily nerve damage, respectively, which limits its use.

Technique

Three separate splanchnic nerves carry sympathetic preganglionic fibers from the different thoracic ganglia: the greatest (T5-T9), the lesser (T10-T11), and the lowest (T12). These nerves descend along the anterior surface of thoracic vertebral bodies to join at the anterolateral surface of T12, subsequently traversing the diaphragm through the crura to form the celiac plexus.

Since all visceral sensory nerves pass through the celiac ganglion, performing splanchnic nerve block carries virtually indistinguishable effects from celiac ganglion block, making it a suitable alternative in cases where the latter is contraindicated. The technique for a splanchnic nerve block is very similar to a transcrural celiac plexus block. However, differences include the retrocrural position of the needle tips and injectate, as well as a higher vertebral level of needle placement.

The procedure is performed in the prone position with a pillow under the abdomen for better anatomical exposure. Once the patient is positioned, the operator will mark the skin 5 to 7 cm lateral of the midline of L1 vertebrae, just below the 12th rib on both sides, serving as needle entry points. After insertion into the subcutaneous tissue, the needle is advanced toward the anterolateral border of the T12 vertebral body under fluoroscopic guidance.

On the lateral view, the needle should project on top of the anterior surface of the T12 body at its superior portion. Contrast should spread in a cephalocaudal direction along the anterolateral vertebral body surfaces. Given negative aspiration, a test dose of 3 to 5 mL of diagnostic or neurolytic (ethanol, phenol) solution should then be injected. If no motor or somatic sensory block signs occur after about five minutes, the remaining 10 to 15 mL of the solution may be administered.

Complications and Adverse Effects

Complications of splanchnic nerve block are identical to those of celiac plexus block (see below), except for a higher risk of pneumothorax and somatic nerve injury due to the proximity of pleura and nerve roots.

Celiac Plexus Block

Specific Indications

Chronic intractable pain, mostly malignant, of foregut and midgut structures (stomach, duodenum, pancreas, biliary system and liver, small intestine)

Technique

The celiac plexus varies anatomically between patients but is typically composed of 1 to 5 anatomically distinct ganglia (celiac, aortic, renal, superior mesenteric) and is located in the upper abdominal retroperitoneum at the level of T12-L1 vertebrae. Preganglionic fibers of the greater, lesser, and least splanchnic nerves make up the celiac ganglion with minor parasympathetic contribution from the vagus nerve. The celiac plexus lies anterior to the diaphragm crura and inferior to the celiac artery. Plexus fibers spread on the anterior and anterolateral sides, surrounding the aorta cephalocaudally and forming the superior and inferior mesenteric plexi. The celiac plexus contributes to the innervation of the abdominal viscera, including the stomach, small bowel, proximal large bowel, spleen, liver, gallbladder, pancreas, kidneys, and adrenal glands.[48]

Anterior, lateral, and posterior (transaortic, periaortic, transcrural, and retrocrural) approaches to blocking the celiac plexus have been described.[49] The posterior transcrural percutaneous approach is the most commonly used by pain physicians, followed by the retrocrural approach (technically a splanchnic nerve block). If the patient has significantly altered anatomy (i.e., a persistent mass in the area of celiac trunk origin, marked scoliosis, or previous extensive abdominal debulking surgery) or if a previous block was unsuccessful, the procedure may be performed using CT guidance.

Venous access and administration of 500 to 1,000 mL crystalloid bolus in anticipation of hypotension is recommended. To perform the posterior transcrural approach, the patient is positioned prone with arms hanging off the bed or above the head, with a pillow under the abdomen to reduce thoracolumbar lordosis. Fluoroscopy or CT guidance is used to distinguish T12 and L1 vertebral bodies. The points 6 to 7 cm inferior and lateral to the transverse process of L1 are marked bilaterally, and the skin overlying these sites is anesthetized.

Under two-plane fluoroscopic guidance, right and left needles are inserted at these marked entry sites and slowly advanced at a 45-degree oblique and slightly cephalad angle, aiming at the L1 vertebral body of the corresponding side. After contacting bone, the depth is noted. Needles are then withdrawn to the subcutaneous tissue, re-advanced at an approximately 30-degree oblique angle, and advanced until the depth of previous bony contact. At that point, under AP and lateral views, the left-sided needle can be walked off the lateral surface of the L1 vertebral body and advanced slowly about 3 to 4 cm.

If aortic pulsation is transmitted to the needle, the needle may either be redirected or a transaortic approach performed. For the right side, the needle is advanced similarly but a bit further, 4 to 5 cm past bony contact. Assuming negative aspiration for blood, urine, or cerebrospinal fluid (CSF), a small amount of contrast is injected and should track close to the midline without lateral spread. Then, a test dose can be given after that. If a lumbar dermatomal motor or sensory block is absent after 5 minutes, the remaining 10 to 15 mL of local anesthetic/neurolytic agent may be administered.

Complications and Adverse Effects

In a meta-analysis performed by Eisenberg et al., the most common adverse effects were local pain (96%), diarrhea (44%), usually limited to the first few days after neurolysis, and hypotension (38%).[50] A few cases of interscapular back pain and hiccups have been reported. Injury to the viscera, aorta, or inferior vena cava and retroperitoneal hematoma may go undetected, as tachycardia and hypotension are viewed as signs of an adequate block.

Although rare, direct or vasogenic nerve injury, infection, intravascular injection, pneumothorax, chylothorax, reactive pleurisy, hematuria, and impotence are also described in the literature. Intrathecal or epidural injection and spread of solution to lumbar plexus or somatic nerves (particularly if a neuroablative chemical was used) can be devastating and lead to paralysis or death. Spasm of lumbar segmental arteries that perfuse the spinal cord has been implicated in the pathogenesis of rare paraplegia due to irritation from phenol or ethanol.

Celiac plexus block may result in serious, non-transient complications in less than 2% of cases.

Lumbar Sympathetic Block

Specific Indications

• Vascular insufficiency of lower extremities (atherosclerotic vascular disease, diabetic vascular insufficiency, Buerger disease, Raynaud disease, arteritis/collagen vascular disease, frostbite, embolisms)
• Sympathetically mediated pain of the lower extremities, kidneys/ureters, genitals
• Complex regional pain syndrome I and II of the lower extremities
• Intractable renal colic
• Urogenital pain
• Post-amputation stump pain
• Phantom limb pain
• Frostbite
• Hyperhidrosis
• Acrocyanosis

Technique

Lumbar sympathetic ganglia consist of 4 or 5 paired nodes on the anterolateral surface of L1-L4 vertebrae, with the densest portion at the L2-L3 level. The lumbar sympathetic chain (LSC) is in very close proximity to lumbar somatic nerves, anterolateral to the lumbar vertebral bodies and anterior to the psoas muscle. On the left, the LSC lies posterolateral to the aorta, and on the right, it lies posterior to the inferior vena cava.[51]

Lumbar sympathetic blocks are typically performed under fluoroscopic guidance but may also use CT guidance.[52] The patient is positioned prone with a pillow under the abdomen to reduce lumbar lordosis. The L3 spinous process is identified radiographically in the AP view. The C-arm is obliqued to a 35- to 45-degree angle, and the skin entry point is identified (an inferolateral aspect of the L3 vertebral body) and anesthetized. A spinal needle (20 to 25 gauge) is advanced to contact the inferolateral aspect of the L3 vertebral body and advanced slowly. AP and lateral images are taken throughout. 

Under lateral view, the needle should be advanced until it lies just anterior to the vertebral body. After negative aspiration, injected contrast should delineate a vacuolated rather than round shape, consistent with the solution expanding in the retroperitoneal space. Contrast should be seen lateral to the vertebral body (lateral view) and anterior to the vertebral body (AP view).

If a strip-like image is produced, the needle is likely in the iliopsoas muscle and should be repositioned. Test dose may be given next, followed by injection of the remaining 10 to 20 mL of anesthetic solution. Blockade at various lumbar levels, or a combination of levels, has been described, with L1 proposed as more adequate for renal or testicular pain and L4-L5 for foot pain. However, the block is most commonly performed at L2, L3, or both levels.

Complications and Adverse Effects

• Hypotension is very common after lumbar sympathetic blocks, especially if bilateral, due to intense vasodilation in the lower extremities and pelvis.
• Bleeding and soreness at the site of injection are typically transient.
• Groin pain and paresthesia may signify genitofemoral neuralgia or nerve injury. The genitofemoral nerve is particularly vulnerable at the L4-L5 level, where it emerges from the psoas major muscle and lies anterior to the fascia close to the sympathetic chain. A genitofemoral nerve block may present as weakness and numbness in the groin, anterior thigh, and quadriceps.
• Damage to the viscera may occur if the needle penetrates retroperitoneal organs (urethra, kidney) or enters the peritoneum.
• Failure to ejaculate and impotence (especially with bilateral blocks), intravascular, epidural, or intrathecal injections, and allergic reactions may also occur. 

Superior Hypogastric Plexus Block

Specific Indications

• Chronic visceral and neuropathic pelvic pain caused by trauma/surgery
• Endometriosis
• Postoperative adhesions
• Inflammatory disease
• Interstitial cystitis
• Sympathetically mediated pelvic or rectal pain
• Postprostatectomy penile and urethral pain
• Malignant pain of the pelvic and rectal viscera that is unresponsive to conservative treatment[53]

Technique

The superior hypogastric plexus is located retroperitoneally, anterior to the L5-S1 vertebral body junction. The common and internal iliac arteries and veins are located on either side of the plexus.

The superior hypogastric plexus block is typically performed using a para spinous technique, though other techniques are also described. The transdiskal approach appears to be equally effective as the classic posterior paraspinal approach. The anterior approach may be easier to perform and may reduce the risk of accidental neurologic injury, as the needle is not near nerve roots. However, it does involve a significant risk of organ and vasculature perforation (bowel, bladder, and pelvic vessels).[54]

To perform the classic para spinous approach, the patient should be positioned prone with a pillow under the pelvis to flex the lumbar spine. Needle insertion sites are marked bilaterally, 5 to 7 cm lateral of the midline at the L4-L5 interspace level. After anesthetizing the skin, a long spinal needle is inserted and advanced at a 30-degree oblique caudal angle toward the anterolateral part of the L5-S1 interspace.

If positioned correctly, the AP radiograph should reveal the tip of the needle at the junction of L5-S1 vertebrae, with contrast spread in the midline region. In the lateral view, the needle tip lies just beyond the anterolateral margin of the L5 vertebral body, with contrast spread anterior to the vertebral body. Assuming negative aspiration and appropriate contrast spread, 6 to 10 mL of local anesthetic or neurolytic agent is injected.

Complications and Adverse Effects

• Injury to the nerve roots or spinal cord
• Bleeding
• Retroperitoneal hematoma
• Perforation of pelvic viscera (including the ureters)
• Intravascular, epidural, and intrathecal injections
• Infection
• Dislodgement of an atherosclerotic plaque from the punctured vessel (the hypogastric nerves lie close to the iliac vessels)
• Retrograde ejaculation, which is usually transient
• Trauma to the intervertebral disk and diskitis is possible with the transdiskcal approach

Ganglion Impar Block (Blockade of the ganglion of Walther)

Specific Indications

• Sympathetically mediated sacral, rectal, anal, genital, vulvar, and perineal pain (ie, malignancy or postherpetic neuralgia)
• Coccydynia
• Pain secondary to endometriosis
• Proctalgia fugax

Technique

The ganglion of Impar is a midline retroperitoneal structure located anterior to the sacrococcygeal junction. It is the most caudal ganglion of the sympathetic chain and provides partial sympathetic innervation to the genitals and pelvic viscera. 

The original technique for ganglion Impar block described by Plancarte et al. proposes the insertion of a manually bent, 22-gauge, 3.5-inch spinal needle just anterior to the tip of the coccyx at the midline (through the anococcygeal ligament).[13] Using AP and lateral fluoroscopic views, the needle is subsequently advanced along the midline toward the sacrococcygeal junction, with the concavity of the needle oriented posteriorly.

Considering the proximity to the posterior rectal wall and the high risk of perforation, insertion of the index finger into the rectum is recommended to help drive the needle tip to the appropriate location. After negative aspiration, contrast is injected to confirm proper positioning and should be visualized on lateral view with spread anterior to the coccyx in the precoccygeal space; then, 4 to 6 mL of anesthetic, neurolytic, or both are administered.

Due to a 20% to 30% failure rate, risk of rectal perforation, intestinal flora translocation, and needlestick injury to the intrarectal finger, the original technique has been replaced by newer ones, such as transcoccygeal, transarticular, and paracoccygeal. The transcoccygeal approach is most popular due to its efficacy and simplicity, though it has been modified since its first description.

The needle-in-needle modification provides advantages such as decreased needle breakage and avoidance of trauma to the disc and coccyx. This technique uses AP and lateral fluoroscopic views to identify the junction between the first and second coccygeal bones. On the lateral view, a short, large-bore needle is advanced at this junction toward the ventral bone surface. Confirmation of needle placement in the midline is necessary before inserting the second needle (22 gauge) within the first.

The second needle is then advanced on lateral view until the tip is visualized just anterior to the coccyx. After negative aspiration, 0.5 to 1 mL of contrast is injected, forming the characteristic “coma sign,” followed by administration of 2 to 4 mL of anesthetic/neurolytic agent.

Complications and Adverse Effects

Proximity to the rectum can lead to visceral trauma and infection if the intestine is perforated. Furthermore, if this occurs, contamination may be tracked along the needle path upon needle removal, leading to fistula formation. Sacral nerve root injury, bladder, rectal and erectile dysfunction, and periosteal injection are possible, though very rare.

Complications

See the technique section above for complications associated with each individual block.

Clinical Significance

Pain is a complex sensation influenced by a variety of factors. On the periphery, it is mostly transmitted by the somatic nerves. Yet, internal organs relay nociceptive information via visceral afferent fibers that travel together with sympathetic nerves. Disrupting these pathways may provide profound analgesia for diseases of internal organs, cancer in particular, and reduce the use of opioid medications.

Activity in the sympathetic efferents can exacerbate some chronic pain states (notably, sympathetically maintained pain of CRPS and ischemic pain), and sympathectomies may effectively relieve these types of pain. Decreasing sympathetic tone by blocking sympathetic ganglia can also be used for treating certain cardiac arrhythmias (sustained ventricular tachycardia), hyperhidrosis, headaches, PTSD, and a variety of other conditions.

Enhancing Healthcare Team Outcomes

Sympathetic blocks are complex and exact procedures requiring imaging equipment and potent medications to ensure optimal outcomes. Thus coherence and closed-loop communication among team members is paramount. The procedure's risks, benefits, alternatives, expectations, and possible complications must be explained to the patient and/or healthcare proxy. Consent must be obtained and appropriately documented.

Collaboration, shared decision-making, and communication are crucial for a good outcome. A timeout involving all interprofessional team members (clinicians, nursing staff, surgical assistants) and the patient is another important step to ensure the correct procedure on the correct anatomic location will be performed; if sedation is to be used, two timeouts should be performed. One occurs prior to sedating the patient while the patient is alert and oriented, and a second should take place just before performing the procedure. It is standard of care to perform sympathetic blocks under direct visualization, with fluoroscopy, ultrasound, and CT guidance commonly used. All interprofessional team members should be empowered to voice any concerns if they notice an issue before, during, and after the procedure.

Providers must be familiar with signs of arising complications and must have the means and knowledge to treat them. Implementation of protocols and pre-made supplies/medication carts (i.e., crash carts) have shown to be very efficacious. New techniques continue to be described. However, data comparing procedural effectiveness usually evolves at a slower pace. Providers should critically evaluate whether or not a new approach is suitable for treating the condition and conforms to the anatomy of the individual patient and whether or not new techniques offer any potential benefits over the established standards.