Sympathetic Neural Blockade

CHAPTER 40 SYMPATHETIC NEURAL BLOCKADE



Meir Chernofsky, MD, Michael Hanania, MD, Charles E. Argoff, MD




1. What distinguishes a sympathetic block from other neural blockade procedures?


The goal of sympathetic blockade is to preserve motor function and touch sensation while selectively blocking the sympathetic nerves. Because sympathetic fibers travel to almost all tissues in the body to innervate the vasculature, almost all nerve blocks involve sympathetic blockade. The separation of somatic and sympathetic function (differential blockade) is sometimes incomplete.



2. What anatomical and physiological factors differentiate sympathetic fibers from somatic fibers? How do the differences affect neural blockade?


Sympathetic fibers are generally thinner than most somatic fibers and are, therefore, more sensitive to anesthetic agents. The cell bodies of somatic motor fibers are located within the central nervous system (CNS), whereas those of the autonomic nervous system are located outside the CNS as postganglionic neurons. The autonomic nervous system is a disynaptic system. The autonomic motor neuron’s location outside of the CNS makes it accessible for local blockade.



3. How can a differential sympathetic blockade be achieved?


There are three general ways to block sympathetic nerves while preserving somatic function:



image Sympathetic nerves are blocked with the same local anesthetic agents (in similar concentrations) used for somatic blockade, but the blocks are performed at anatomic locations where sympathetic nerves are separate and distinct from somatic nerves. Examples of such locations are the stellate ganglion and the lumbar sympathetic ganglion.


image The block is performed at locations that combine somatic and sympathetic nerve fibers, but low concentrations of local anesthetic are used. Because postsynaptic sympathetic nerves are small and unmyelinated, they are more sensitive than some larger or myelinated somatic fibers to dilute local anesthetic. This approach is useful for spinal and epidural blockade.


image Specific sympathetic antagonists are employed. For example, the antihypertensive agent guanethidine can be injected into the vasculature of a limb, with a tourniquet applied and inflated to a pressure greater than the systolic arterial pressure. After a short period during which the agent has had a chance to distribute into local tissues, the tourniquet is deflated, and a local selective lysis of sympathetic function has been achieved. This technique is a variation of intravenous regional anesthesia, the Bier block. It is usually a poor choice if ischemia is the primary problem.



4. What is the general role of sympathetic blockade in pain management?


Sympathetic blocks can be helpful for four types of clinical problems:



image In some body regions, afferent pain fibers travel with sympathetic nerves. For example, the fibers that conduct painful impulses from the pancreas are closely associated with the celiac plexus. Therefore neural blockade of the celiac plexus is a convenient way to provide pancreatic analgesia. The primary target of such a procedure is the afferent fibers that travel with the sympathetic trunk, although a sympathetic role in the maintenance of such pain has not been ruled out.


image The sympathetic nervous system (SNS) is believed to play a primary role in a certain class of painful syndromes. Directed blockade of the sympathetic fibers may be both diagnostic and therapeutic in cases of sympathetically maintained pain.


image Physicians skilled in neural blockade are occasionally asked to become involved in the treatment of ischemic syndromes of the limbs. The patient may or may not have pain, and the SNS is not implicated in the pathologic process. However, by inducing sympathetic neural blockade, the tonic baseline level of arterial vasoconstriction is reduced. Depending on the vascular pathology, blood flow to the ischemic area may be improved.


image There is also a grab-bag of indications for sympathetic blockade that do not fit into one of the above categories. For example, stellate ganglion block (see Question 10) may be useful in the diagnosis and treatment of certain cardiac dysrhythmias related to prolonged QT syndrome.



5. Without going into specific indications just yet, what are some of the common types of sympathetic blocks?


Blocks that take advantage of isolating the sympathetic fibers at sympathetic plexi or trunks include the so-called stellate ganglion block, the lumbar sympathetic block, the celiac plexus block, and the hypogastric plexus block. Techniques that exploit the potential of differential blockade by using low concentrations of local anesthetics include differential spinal and epidural blocks. Agents used in the Bier technique in the upper or lower extremity include reserpine, guanethidine, and the ganglionic agent bretylium. Finally, almost all somatic nerve blocks also block sympathetic nerves.



6. What is reflex sympathetic dystrophy (RSD)?


Reflex sympathetic dystrophy (RSD) is now termed complex regional pain syndrome type 1 (CRPS-1) as opposed to CRPS type 2, which was previously labeled as causalgia. It is a syndrome of pain and disability (altered sensory, motor, and sympathetic neural function) usually, but not always in a distal extremity. It is characterized by decreased function and signs of sympathetic overactivity. CRPS-1 is usually initiated by trauma. The degree of the initial trauma may vary from a major fracture with neurovascular injury to a trauma so minor that it is not recalled by the patient. In patients with major nerve injury CRPS-2 is more usual. Various medical conditions, such as stroke and myocardial infarction, also may be inciting factors.



7. What does CRPS-1 look like clinically?


CRPS-1 is a chronic, progressively evolving syndrome with different signs at different stages. Pain and decreased function are present at all stages. Initially, there may be signs of sympathetic overactivity, such as increased sweating in the affected part. The area may be a dusky blue color, although color change may be intermittent. As the condition progresses, some of these signs become less obvious, and atrophy becomes more prominent. The extremity, more commonly the hand, becomes hypersensitive and tender and is guarded by the patient. In the late stages, there is radiologic evidence of bone thinning (Sudeck’s atrophy), which may be contributed to by underuse of the affected part.



8. What is the role of the sympathetic nervous system in CRPS-1?


The clinical signs and the marked relief after sympathetic block in early cases points to sympathetic overactivity as an important factor in maintenance and perhaps initiation of CRPS-1. However, this mechanism has recently been called into question. Where the syndrome does respond to sympathetic block, the term “sympathetically maintained pain” is used to distinguish it from those cases where sympathetic block has no effect (“sympathetic independent pain”).



9. True or false: Treatment of CRPS-1 is effective at any stage of the disease


False. Treatment of CRPS type 1 becomes less satisfactory in the later stages of disease. When the condition is neglected, it may progress to a disability that dominates the life of the patient. Patients may become so desperate that they request amputation. Unfortunately, early surgical adventures with amputation demonstrated that a chronic pain syndrome remains even after the limb is gone. Therefore, early diagnosis, with a trial of therapy when possible, is important.



10. What is a stellate ganglion block?


There is a series of sympathetic ganglia on either side of the cervical vertebral column and on either side of the thoracic vertebrae. The stellate ganglion is less a consistent anatomic structure than a general area in which the inferior cervical ganglia and first thoracic ganglia are fused—or at least in close proximity.


Virtually the entire sympathetic nerve supply to the head and neck synapses in or near the stellate ganglion. A good portion of the sympathetic innervation to the ipsilateral upper extremity also synapses in the stellate ganglion, with the remainder synapsing in adjacent ganglia. A consistent blockade of the head, neck, and upper extremity sympathetic innervation may be achieved by applying a quantity of local anesthetic (5 to 12 mL) to the area of the stellate ganglion. When the proper quantity of local anesthetic is used, spread to adjacent ganglia is common, leading to reliable upper extremity sympathectomy.



11. How is a stellate ganglion block performed?


The most common technique for performing a stellate ganglion block is an anterior neck approach. The patient is placed in the supine position, and the neck is extended as tolerated. After antiseptic preparation, a 3-cm needle (22-23 gauge) is introduced perpendicular to the skin (and perpendicular to the floor) at the level of the cricoid cartilage between the trachea and the anterior border of the sternocleidomastoid muscle. Retracting the sternocleidomastoid muscle laterally and palpating the anterior aspect of the C6 vertebra with two fingers facilitates introduction of the needle and avoids puncture of the carotid artery. The needle is advanced until bone is encountered. If bone is not encountered at this location, the needle is withdrawn to the subcutaneous tissues and reintroduced in a slightly caudad or cephalad direction.


When bone is encountered, the needle is withdrawn about 0.5 cm. (If this step is not done, a higher incidence of somatic blockade of the upper extremity will result.) After careful aspiration testing is negative for blood or cerebrospinal fluid, 5 to 12 ml of local anesthetic is introduced in fractional doses, and the needle is withdrawn. Given the close proximity of important structures, intravenous access should be in place and appropriate cardiovascular monitoring performed.



12. What are the contraindications to stellate ganglion block?


Most of the contraindications to stellate ganglion block are a matter of common sense and are relative rather than absolute. Patients who are anticoagulated or taking high-dose aspirin are at increased risk for bleeding. A local infection over the proposed site of injection is a somewhat more absolute contraindication. Patients with bullous disease of the upper lobes of the lung are at greater risk for accidental pneumothorax and must be approached with more caution. Because one of the possible complications of stellate ganglion block is vocal cord paralysis, patients with contralateral vocal cord paralysis are at risk for severe airway abnormality if the ipsilateral cord becomes paralyzed. Patients who have abnormal anatomy because of prior surgery or injury present greater technical difficulty because of the differences in anatomic landmarks. Such patients are probably better approached using fluoroscopic guidance and contrast dye or with alternative techniques, such as intravenous regional sympatholysis.



13. What are the side effects of a stellate ganglion block?


Stellate ganglion block causes sympathetic blockade of the ipsilateral face and arm. Therefore, a successful block produces an ipsilateral Horner’s syndrome (ptosis, miosis, and anhydrosis), flushing of the face, and increased temperature of the arm. These effects are normal and last for the duration of the blockade. Slightly blurred vision and a sense of fullness around the eye may result. Local trauma from the blockade or blockade of the recurrent laryngeal nerve may produce hoarseness. Neck tenderness is fairly common, but frank hematoma is less likely. In severe cases, hematoma may threaten the airway.



14. What are the risks of a stellate ganglion block?


Inadvertent blockade of components of the brachial plexus may lead to upper extremity numbness and weakness or paralysis, both temporary in the vast majority of cases. If pain relief occurs in the presence of somatic blockade, the pain syndrome may have been due to a peripheral lesion, but a sympathetic origin cannot be inferred. Passive ranging of the painful joints may be dangerous in the face of somatic blockade because pain, which may warn of extreme passive strain on a structure, is blocked.


Serious complications of stellate ganglion blockade include carotid puncture with hematoma and vertebral artery puncture. Introduction of even small amounts of local anesthetic into either of these arteries may lead to seizures (usually short-lived). Introduction of small amounts of local anesthetic into the cerebrospinal fluid may lead to high (or total) subarachnoid neural blockade with respiratory arrest, coma, hypotension, and sometimes cardiac arrest. A generalized toxic reaction to the local anesthetic load also may occur if too much local agent gains access to the circulation too fast. If the needle enters too inferiorly, a pneumothorax may occur. Late complications include the remote possibility of mediastinitis after puncture of the esophagus and the possibility of late airway compromise from hematoma or trauma.



15. How can the complications mentioned in questions 13 and 14 be prevented or managed?


There is no foolproof way to avoid complications of a stellate ganglion block. The incidence of complications may be reduced by proper training and experience. However, the chance of permanent injury to the patient as a result of seizure, accidental spinal anesthesia, or pneumothorax can certainly be reduced to acceptable levels with proper preparation, including the following:



1. Perform the block only on fasting patients to avoid aspiration in case of loss of consciousness.


2. Perform the block only in a setting in which an anesthesiologist (or an emergency physician with excellent airway management skills) is immediately available to manage complications.


3. Start an intravenous lifeline in every patient before the block is attempted so that emergency drugs can be administered without delay.


4. Perform the block with monitoring of blood pressure, cardiac rate and rhythm, and oxygen saturation.


5. Administer supplemental oxygen to all patients, or have it immediately available in case of signs of trouble.


6. Have an emergency airway cart and emergency drugs available.


7. Take all complaints from the patient seriously, and have a high index of suspicion for pneumothorax.



16. What is the role of the stellate ganglion block in treatment of CRPS-1?


In cases of suspected upper extremity CRPS-1, an initial block can be performed with a short-acting local anesthetic such as lidocaine 1%. This initial block is diagnostic; its purpose is to determine whether the block is technically feasible, produces sympathetic blockade of the upper extremity, and results in (1) subjective pain relief, (2) any increase in functional ability of the hand, or (3) objective signs of improvement on examination and functional testing.


If the first block is successful either subjectively or objectively, a series of blocks may provide sufficient relief for appropriate physical therapy. After each block, a physical therapist works with the patient to achieve functional improvement. Behavioral therapy is an important adjunct to the therapy.



17. Which somatic nerve is most likely to be blocked unintentionally in attempting a stellate ganglion block?

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Jun 14, 2016 | Posted by in PAIN MEDICINE | Comments Off on Sympathetic Neural Blockade

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