Ablative Nerve Block

As with other interventional spinal procedures, only physicians specifically trained in fluoroscopically guidance procedures should perform radiofrequency ablation. Qualified physicians typically undergo residency training in the fields of Anesthesiology, Physiatry, Neurology, Psychiatry, or Neurosurgery. This is followed by an interventional pain or spine fellowship that allows adequate training under an experienced interventionalist prior to performing the procedure independently. Support staff for the procedure can include an assistant to draw up medications and operate the radiofrequency generator and radiology technician to operate the C-arm, under the guidance of the practicing physician.

The destruction of tissue via radiofrequency must occur after successful diagnostic anesthetic nerve blocks have located the target nerve. During the procedure, the patient should receive little to no sedation, as they must define what they are experiencing during stimulation and lesioning of the nerve.

1. The patient is placed in a comfortable position with adequate exposure of the region overlying the target nerve. The skin is cleaned and prepped, and the target is found using fluoroscopy. A small amount of local anesthetic is injected subcutaneously at the point of needle insertion.
2. The introducer needle is then inserted through the skin, subcutaneous tissue, and muscle toward the target using fluoroscopy to guide the trajectory.
3. Once the tip of the needle is placed satisfactorily close to the target, the active electrode is inserted through the needle.
4. Sensory stimulation is used at first, to recreate the painful symptoms that the patient experiences, thus locating the target. 
5. This is followed by motor stimulation to ensure that the active tip is not close to the motor nerves.
6. Once confirmed, the generator produces a continuous output of voltage at the tip of the electrode, where it will be kept at 80 degrees Celsius for approximately one minute, creating a zone of thermally induced coagulation.

Nerve ablation is a minimally invasive, relatively low-risk procedure. There is a limited side effect profile to ablative nerve blocks.[10] However, adverse events may occur during the placement of the introducer needle or during the ablative process. Advancement of the introducer needle has the potential to cause vascular or neural insult along the trajectory that it is traveling, while the process of thermal ablation may lead to burns (due to errors in ground pad placement), worsened pain, sensory loss or new-onset neuropathic pain.[11][12]

Complications are most common after intracranial ablation of the trigeminal ganglion, which may manifest as facial numbness, dysesthesia, anesthesia dolorosa, corneal anesthesia, keratitis, and trigeminal motor dysfunction.

Adverse events from ablation of lumbar medial branches are far and few between with transient postoperative pain dominating as the premier adverse event.

As with any invasive technique, the risk of allergy to materials or anesthetic, hematoma formation, and infection must be considered.

One hundred million Americans suffer from some form of chronic pain that results in more than $100 billion in expenses annually. Furthermore, 84% of American adults will suffer from chronic, low-back pain at some point in their lifetime. While the causes of low-back pain are often multifactorial and can be due to many causes, the degenerative cascade that affects the spine plays a significant role. Destruction of cartilage that comprises the spinal facet joints results in severe discomfort when placed under stress, typically in extension or rotation of the spine. The sensory nerves responsible are the medial branches of the dorsal rami, which are the most common target in ablative procedures. Radiofrequency ablation has been shown to be efficacious in reducing the severity of back pain for extended periods of time (ranging from 6 months to 24 months in duration) but also has utility in the treatment of trigeminal and occipital neuralgia, complex regional pain syndrome, hip and knee osteoarthritis, and plantar fasciitis. As with other interventional procedures that provide pain relief, ablation aims to play a significant role in the reduction of opiates and other habit-forming pain medications.

This review focuses on the use of conventional radiofrequency ablation, which utilizes a continuous energy source causing coagulative thermal necrosis. Other forms of ablation used in pain management include:

• Pulsed radiofrequency: Applies heat in a pulsatile manner, but uses lower temperatures in a than conventional radiofrequency to avoid neurolysis.
• Cooled radiofrequency: Utilizes specialized electrodes that are cooled with water-flowing along its shaft, but not at the active tip. This allows higher temperatures and more spherical lesion sizes to be achieved at the target site and less risk of tissue damage superficial to the target.
• Cryoablation: Causes the destruction of axons by disrupting the vasa nervorum. It is increasing in popularity due to a decreased incidence of post-procedural hyperalgesia and neuroma formation compared to conventional radiofrequency.

Cases of the use of ablative nerve blocks have been used for intercostal neuralgia with success.[13] Ablative nerve blocks of the genicular nerve for chronic new pain, have also been shown to be an effective pain reliever for chronic, refractory knee pain.[14] Patients who undergo ablation of the genicular nerve have been shown to have proved pain for up to six months following the procedure.[15] Furthermore, studies have been done regarding the effectiveness of ablative techniques on cancer pain as well. Results have shown blocks to be effective for upper abdominal cancers such as gastric or pancreatic cancer.[16] Chronic pericranial headache pain has also been studied and shows evidence of the use of radiofrequency ablation of the pericranial nerves.[17] One promising 2016 study looked at radiofrequency ablation in the treatment of vertebral compression fractures as well. However, more studies need to be done.[18] There is limited effectiveness for the use of ablative nerve blocks for facet joint osteoarthritis compared to placebo.[19]

Nerve ablation for back pain is commonly done as an outpatient, but still requires the efforts of an interprofessional team. While the actual ablation is done by a physician, patient monitoring is frequently done by a dedicated nurse/nurse anesthetist. The patient must have the vital signs monitored at regular intervals and if any sedation is used, the pulse oximeter must be continuously monitored; these duties will often fall to the nursing staff, to report any incongruities promptly. Intravenous access should be in place in case the patient develops hypotension or requires more sedation. Finally, if conscious sedation is used, the antidotes to the medications used must be in the room. After the procedure, the patient should be monitored in the recovery room for several hours by the post-anesthesia recovery nurse. Before discharge, the patient should be informed about the possible side effects of the procedure and when to return to the hospital. Interprofessional teamwork will result in improved patient outcomes. [Level 5][20]