Nerve block or regional nerve blockade is the deliberate interruption of signals traveling along a nerve, often for the purpose of pain relief.
Local anesthetic nerve block is a short-term block, usually lasting hours or days, involving the injection of an anesthetic, a corticosteroid, and other agents onto or near a nerve.
Neurolytic block, the deliberate temporary degeneration of nerve fibers through the application of chemicals, heat, or freezing, produces a block that may persist for weeks, months, or indefinitely.
Neurectomy, the cutting through or removal of a nerve or a section of a nerve, usually produces a permanent block.
Because neurectomy of a sensory nerve is often followed, months later, by the emergence of new, more intense pain, sensory nerve neurectomy is rarely performed.
The concept of nerve block sometimes includes central nerve block, which includes epidural and spinal anaesthesia.
Local anesthetic nerve block is a short-term nerve block involving the injection of local anesthetic as close to the nerve as possible for pain relief.
The local anesthetic bathes the nerve and numbs the area of the body that is supplied by that nerve.
The goal of the nerve block is to prevent pain by blocking the transmission of pain signals from the affected area.
Local anesthetic is often combined with other drugs to potentiate or prolong the analgesia produced by the nerve block.
These adjuvants may include epinephrine (alpha-adrenergic agonists), corticosteroids, opioids, or ketamine.
These blocks can be either single treatments, multiple injections over a period of time, or continuous infusions.
A continuous peripheral nerve block can be introduced into a limb undergoing surgery –a femoral nerve block to prevent pain in knee replacement.
Regional blocks can be used for procedural anesthesia, post-operative analgesia, and treatment of acute pain in the emergency room.
Regional blocks can be an alternative to general anesthesia as well as oral pain medications.
Regional blocks can provide complete relief of pain along a nerve distribution and can lead to a reduction in the amount of opiates needed.
Advantages over general anesthesia include faster recovery and less need for monitoring.
Nerve blocks can be used for the diagnosis of surgically treatable chronic pain.
Advances in surgical techniques such as minimally invasive surgery have made virtually all peripheral nerves surgically accessible.
Any nerve that can be blocked can now be treated with a nerve decompression.
Imaging such as MRI has poor correlation with clinical diagnosis of nerve entrapment as well as intraoperative findings of decompression surgeries and so diagnostic blocks are used for surgical planning.
Local anesthetic nerve blocks are sterile procedures usually performed in an outpatient facility or hospital, with the help of ultrasound, fluoroscopy, CT, or MRI/MRN to guide the practitioner in the placement of the needle.
Landmark-guided nerve blocks use palpable anatomical landmarks and a working knowledge of the superficial and deep anatomy to determine where to place the needle.
Although a peripheral nerve stimulator can facilitate placement of the block, it is designed to elicit a motor response rather than creating a paresthesia, making it less effective for identifying purely sensory nerves.
Landmark-guided injections have largely been replaced with image guidance due to increased accuracy, but there are some nerves for which landmark-guidance still has comparable accuracy, such as the pudendal nerve.
Fluoroscopy uses X-rays to obtain real-time moving planar images of the interior of an object. In this sense, fluoroscopy is a continuous x-ray.
Landmark-guided injections except that the landmarks are based on radiographic anatomy.
There is poor soft tissue contrast, meaning that nerves cannot be clearly visualized, but nerves that are situated by bony landmarks can be good candidates, such as epidural steroid injections, which target the spinal nerves.
The radiation involved is higher than an x-ray, but lower than a CT-guided injection, which is itself lower than a full CT scan.
One study found about 0.40 mSv exposure per minute of fluoroscopy for up to 3 minutes.
Ultrasound-guided peripheral nerve block is a procedure that allows real-time imaging of the positions of the targeted nerve, needle, and surrounding vasculature and other anatomical structures: this visual aid increases the success rate of the block and may reduce the risk of complications.
It may also reduce the amount of local anesthetic required, while reducing the onset time of blocks.
Ultrasound has also resulted in an exponential rise in fascial plane blocks.
Ultrasound is particularly well-suited for regional anesthesia: anesthesia targets (e.g., brachial plexus, femoral nerve) have large blood vessels that travel with the target nerves.
Direct visualization of nerves is not just important for localization ensures that the injected material surrounds the nerve.
Visualization of blood vessels is important to ensure that needle placement avoids blood vessels, which often travel directly parallel to nerves.
Ultrasound machine is generally portable and inexpensive.
Ultrasound limitations:
First an acoustic window is required, and certain tissue types such as bone can interfere with image acquisition.
CT and MRI have standard slicing orientations-sagittal, coronal, axial, but for ultrasound the orientation of the 2D image depends on the position and orientation of a probe held by the operator.
Ultrasound has a tradeoff between penetration depth and resolution.
Higher frequencies provide better resolution but have less penetration depth.
The limited penetration depth and resolution tends to make ultrasound a poor choice in particular for deeply situated pelvic nerves.
CT provides excellent spatial resolution and good soft-tissue contrast, making it easy to verify the anatomic level.
While the use of CT does expose the patient to radiation, the amount of radiation is less than a full scan.
Radiation from a lumbar spine CT is approximately 7.5 mSv, but the radiation from standard protocols for CT-guided epidurals is about 1.3-1.5 mSv.
A low-dose CT protocol may still provide the required resolution, and if used can reduce the radiation exposure by another 85%, bringing the radiation exposure to about 0.2 mSv.
MRI provides excellent visualization of soft tissues, but the detail is not usually enough to see the small nerves that are often entrapped.
MR neurography has increased the level of nerve details seen and allowed for more accurate MRI-directed injections.
Local anesthetics are broken down into two categories: ester-linked and amide-linked.
The esters include benzocaine, procaine, tetracaine, and chloroprocaine.
The amides include lidocaine, mepivacaine, prilocaine, bupivacaine, ropivacaine, and levobupivacaine.
Chloroprocaine is a short-acting drug (45–90 minutes), lidocaine and mepivacaine are intermediate duration (90–180 minutes), and bupivacaine, levobupivacaine, and ropivacaine are long-acting (4–18 hours).
Drugs commonly used for peripheral nerve blocks include lidocaine, ropivacaine, bupivacaine, and mepivacaine.
Local anesthetics act on the voltage-gated sodium channels that conduct electrical impulses and mediate fast depolarization along nerves.
Local anesthetics also act on potassium channels, but they block sodium channels more.
Lidocaine preferentially binds to the inactivated state of voltage-gated sodium channels, but has also been found to bind potassium channels, G protein-coupled receptors, NMDA receptors, and calcium channels in vitro.
The duration of the block is mostly influenced by the amount of time the anesthetic is near the nerve.
Lipid solubility, blood flow in the tissue, and presence of vasoconstrictors with the anesthetic all play a role in this.
A higher lipid solubility makes the anesthetic more potent and have a longer duration of action; however, it also increases the toxicity of the drug.
Local anaesthetics are often combined with adjuvants, drugs that boost the effect of each other, with the end goal of increasing the duration of the analgesia or shortening time of onset.
Such adjuvants may include epinephrine, clonidine, and dexmedetomidine.
Vasoconstriction caused by local anesthetic may be further enhanced synergistically with the addition of epinephrine, the most widely used additive.
Epinephrine increases the length of analgesic duration and decreases blood flow by acting as an agonist at the α1-adrenoceptor.
The addition of dexamethasone to a nerve block or if given intravenously for surgery can prolong the duration of an upper limb nerve block leading to reduction in postoperative opioid consumption.
There are short acting (45–90 minutes), intermediate duration (90–180 minutes), and long acting anesthetics (4–18 hours).
Block duration can be prolonged with use of a vasoconstrictor such as epinephrine, which decreases the diffusion of the anesthetic away from the nerve.
Therapeutic blocks may be used for acute pain patients, diagnostic blocks are used to find pain sources, prognostic blocks are used to determine subsequent pain management options, preemptive blocks minimize postoperative pain, and some blocks can be used in place of surgery.
Certain surgeries may benefit from placing a catheter that stays in place for 2–3 days postoperatively.
Catheters are indicated for some surgeries where the expected postoperative pain lasts longer than 15–20 hours.
Nerve blocks may also reduce the risk of developing persistent postoperative pain several months after surgery.
Local anesthetic nerve blocks are sterile procedures that can be performed guided with the help of anatomical landmarks, ultrasound, fluoroscopy (a live X-ray), or CT.
Electrical stimulation can also provide feedback on the proximity of the needle to the target nerve.
Complications of nerve blocks most commonly include infection, bleeding, and block failure.
Nerve injury is a rare side effect occurring roughly 0.03–0.2% of the time.
Local anesthetic toxicity, the most dangerous complication, is often first detected by symptoms of numbness and tingling around the mouth, metallic taste, or ringing in the ears.
Local anesthetic toxicity, it may lead to seizures, arrhythmias, and may progress to cardiac arrest.
Local anesthetic toxicity may arise from an allergy, excessive dose, or intravascular injection.
Local anesthetic systemic toxicity can include neurologic and cardiovascular symptoms including cardiovascular collapse and death.
Transient tachycardia may result if epinephrine is administered in the block.
Procedures done under local anesthesia carry a lower anesthetic risk than general anesthesia.
The use of ultrasound and nerve stimulation has greatly improved practitioners’ ability to safely administer nerve blocks.
Nerve injury most often occurs from ischemia, compression, direct neurotoxicity, needle laceration, and inflammation.
A form of nerve block involves the deliberate injury of a nerve by freezing or heating, the application of chemicals as alcohol or phenol in glycerin.
These interventions cause degeneration of the nerve’s fibers and temporary interference with the transmission of nerve signals.
With such procedures, the thin protective layer around the nerve fiber, the basal lamina, is preserved so that, as a damaged fiber regrows, it travels within its basal lamina tube and connects with the correct loose end, and function may be restored.
Surgical cutting of a nerve, a neurectomy, severs these basal lamina tubes, and without them to channel the regrowing fibers to their lost connections transmission of nerve signals persist.
Over time, however, a painful neuroma or deafferentation pain may develop.
This is why the neurolytic is usually preferred over the surgical block.
The neurolytic block is sometimes used to temporarily reduce or eliminate pain in part of the body.
Neurolytic block sites include; the celiac plexus, most commonly for cancer of the gastrointestinal tract up to the transverse colon, and pancreatic cancer, but also for stomach cancer, gall bladder cancer, adrenal mass, common bile duct cancer, chronic pancreatitis and active intermittent porphyria; the splanchnic nerve, for retroperitoneal pain, and similar conditions to those addressed by the celiac plexus block but, because of its higher rate of complications, used only if the celiac plexus block is not producing adequate relief; the hypogastric plexus, for cancer affecting the descending colon, sigmoid colon and rectum, as well as cancers of the bladder, prostatic urethra, prostate, seminal vesicles, testicles, uterus, ovary and vaginal fundus; the ganglion impar, for the perinium, vulva, anus, distal rectum, distal urethra, and distal third of the vagina: the stellate ganglion, usually for head and neck cancer, or sympathetically mediated arm and hand pain; the triangle of auscultation for pain from rib fractures and post thoracotomy using a rhomboid intercostal block the intercostal nerves, which serve the skin of the chest and abdomen and a dorsal root ganglion may be treated by targeting the root inside the subarachnoid cavity, most effective for pain in the chest or abdominal wall, but also used for other areas including arm/hand or leg/foot pain.
Neurectomy is a surgical procedure in which a nerve or section of a nerve is severed or removed.
Cutting a sensory nerve severs its basal lamina tubes, and without them to channel the regrowing fibers to their lost connections, over time a painful neuroma or deafferentation pain may develop.
This is why the neurolytic is usually preferred over the surgical sensory nerve block.
This surgery is performed in rare cases of severe chronic pain where no other treatments have been successful.
A local anesthetic nerve block is usually performed before the actual neurectomy to determine efficacy and detect side effects.
The patient is typically under general anesthetic during the neurectomy, which is performed by a neurosurgeon.
Regional blocks
The brachial plexus is a bundle of nerves innervating the shoulder and arm and can be blocked at different levels depending on the type of upper extremity surgery being performed. Interscalene brachial plexus blocks can be done before shoulder, arm, and elbow surgery.
The interscalene block is done at the neck where the brachial plexus emerges between the anterior and middle scalene muscles.
The needle goes in about 3–4 cm and a single shot of local anesthetic is injected or a catheter is placed.
The most common local anesthetics used at the site of the nerves are bupivicaine, mepivicaine, and chloroprocaine.
With this block there is a very high chance that the phrenic nerve, which innervates the diaphragm, will be blocked so this block should only be done on patients who have use of their accessory respiratory muscles.
The block may not affect the C8 and T1 roots which supply part of the hand, so it is usually not done for hand surgeries.
The supraclavicular and infraclavicular blocks can be performed for surgeries on the humerus, elbow, and hand.
These blocks provide different views of the nerves, so it depends on the individual patient’s anatomy to determine which block should be performed.
A pneumothorax is a risk with these blocks.
An axillary block is indicated for elbow, forearm, and hand surgery, as it anesthetizes the median, ulnar, and radial nerves.
This block is less risk than the interscalene spinal cord or vertebral artery puncture or supraclavicular brachial plexus blocks.
Lumbar plexus innervates the lower extremity.
Fascia iliaca block is indicated for pain relief for hip fractures in adults and femoral fractures in children, works by affecting the femoral, obturator and the lateral cutaneous nerves.
The femoral nerve block is indicated for femur, anterior thigh, and knee surgery, and It is performed slightly inferior to the inguinal ligament, and the nerve is under the fascia iliaca.
Peripheral nerve blockade for hip fractures involves injection of a local anesthetic close to the sensory nerve supplying the anterior capsule of hip joint, which is the main source of postoperative pain.
Key nerves involved in sensory innovation of the interior capsule include the femoral, obturator, and accessory obturator nerves.
For effective pain control, peripheral nerve blocks, use local and aesthetics with prolong duration of action, such as buvacaine and ropivacaine.
The sciatic nerve block is done for surgeries at or below the knee, and The nerve is located in the gluteus maximus muscle.
The popliteal block is done for ankle, achilles tendon, and foot surgery.
It is done above the knee on the posterior leg where the sciatic nerve starts splitting into the common peroneal and tibial nerves.
The saphenous nerve block is often done in combination with the popliteal block for surgeries below the knee, and is at the medial part of the lower thigh under the sartorius muscle.
The lumbar plexus block is an advanced technique indicated for hip, anterior thigh, and knee surgery.
The lumbar plexus is composed of nerves originating from L1 to L4 spinal roots such as the iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, and obturator nerves.
The lumbar plexus is located deep, and there is an increased risk of local anesthetic toxicity, so less toxic anesthetics are often recommended.
Genicular nerve block: Temporary anesthesia of genicular (knee) sensory nerves is used as a diagnostic procedure to help determine whether or not a person with chronic severe knee pain may be a candidate for more durable treatment with radiofrequency ablation.
Needles are placed near branches of the genicular nerves, which are then anesthetized with a short-lasting anesthetic, such as lidocaine.
Although selection of the genicular nerve branches or other sensory nerves may vary by clinician experience, blocking the superior lateral, superior medial, and inferior medial genicular nerves has proven successful for reducing knee pain.
Following genicular nerve block, knee pain is monitored over hours to days when the local anesthetic is blocking the knee joint pain.
In people who experience a significant alleviation of knee pain with this diagnostic test, radiofrequency ablation of the same genicular nerves can then be performed as a treatment for long-lasting pain relief, which may persist over several months to two years.
The paravertebral nerve block can be used for various surgeries depending on the vertebral level it is done.
A block at the neck in the cervical region is useful for thyroid gland and carotid artery surgery.
At the chest and abdomen in the thoracic region, blocks are used for breast, thoracic, and abdominal surgery.
A block at the hip in the lumbar region is indicated for hip, knee, and anterior thigh surgeries.
The paravertebral block provides unilateral analgesia, but bilateral blocks can be performed for abdominal surgeries.
It may be chosen over epidurals for patients who cannot tolerate the hypotension that follows bilateral sympathectomy.
The paravertebral space is located a couple centimeters lateral to the spinous process and is bounded posteriorly by the superior costotransverse ligament and anteriorly by the parietal pleura.
Complications include pneumothorax, vascular puncture, hypotension, and pleural puncture.
The erector spinae plan block is sometimes suggested for thoracic-related pain control to reduce the need for opioids after surgery.
This block can provide pain control for breast surgery, rib fractures and chest-wall related pain.
This block may also be applied at lower levels of the spine-lumbar and sacral levels, to target pelvic abdominal regions of the body that require pain relief.
There is also some evidence that this block may be helpful for managing pain in conditions and procedures such as pancreatitis and appendicitis, thoracotomy, hernia repairs, lumbar fusion surgery, pectus excavatum treatment, and kidney stone removal procedures.