Required patient participation
Epidural Steroid Injection
Must move lower extremities after lidocaine test dose
Paraplegia secondary to arterial steroid injection
Medial Branch Block
Critical during sensory and motor testing
Intrathecal or epidural injection
Critical during sensory and motor testing
Thermal motor nerve injury
MAC, spinal, or GA
Over-sedation or spinal anesthesia may mask new neurologic deficits
Neurologic injury, baclofen toxicity
Spinal Cord Stimulator
Lateral or prone
Communication of paresthesias/coverage
Post-dural puncture headache, arrhythmia
Medial Branch Radiofrequency Ablation
With the patient in the prone position, the tip of the radiofrequency probe is guided to the junction of the transverse process and lateral neck of the superior articular process in an orientation parallel to the nerve branch. After needle positioning is confirmed visually, sensory and motor testing is carried out. Sensory testing involves administering an electric current to reproduce the patient’s baseline pain and confirm the diagnosis. Motor testing is conducted to ensure the needle tip is far enough away from the motor fibers to avoid inadvertant injury. It is critical that the patient is able to communicate with the proceduralist during sensory and motor testing. Over-sedation at this point of the procedure can have devastating consequences. Permanent motor deficits may result from thermal injury of motor nerves if patients can’t effectively participate in sensory and motor testing. The patient should be counselled preoperatively regarding the importance of minimal sedation during sensory and motor testing. Careful communication and re-assurance during the procedure is critical. Lidocaine is typically administered through the cannula once proper position is confirmed, however, thermal ablation may be painful and more sedation may be required during this part of the procedure.
Prior to proceeding to radiofrequency ablation of the medial branch nerves in the thoracic, lumbar or cervical spines, it is standard practice to perform two sets of diagnostic medial branch nerve blocks. If both sets are positive, it is presumed with reasonable certainty that the facet joints are the pain generators and that thermal destruction of these nerves would provide the patient with considerable pain relief. Diagnostic medial branch nerve blocks are typically performed using local anesthetics of relatively short duration including lidocaine and bupivacaine. After the injection is performed, the patients are asked to engage themselves in activities, which, under normal circumstances, would provoke pain . If excessive sedation is administered to these patients, they may not be alert enough to appreciate and record their pain levels during the duration of action of the administered local anesthetic. As a result of this, there exists the possibility that patients will perceive decreased pain scores that may be attributable to the sedatives administered rather than the local anesthetic itself. A physician relying on information from these diagnostic blocks may perform a radiofrequency ablation with less than expected subsequent pain relief.
Lumbar Transforaminal Epidural Steroid Injections
This procedure is performed when patients experience pain in a specific dermatome. A spinal needle is advanced under the pedicle, medial to the pars interacticularis using fluoroscopic guidance. At this point a mixture of local anesthetic and steroids is injected. The anterior thoracolumbar spinal cord is heavily dependent on the anterior spinal artery, which is in turn highly dependent on the contribution from the large and variably located radiculomedullary artery (artery of Adamkiewicz). Injection of a particulate steroid into this artery can result in paraplegia. Therefore, prior to injecting any particulate steroid, a test dose of 1 % lidocaine is administered. One minute after the test dose the patient is asked to move their lower extremities. Successful leg movement rules out intravascular needle position. It is absolutely critical that this test dose and movement test not be inhibited or impacted by over-sedation. Prior to the test dose, the anesthesiologist and pain physician should communicate to ensure an appropriate level of sedation, and the patient should be counselled about the test dose preoperatively.
Spinal Cord Stimulation
A spinal cord stimulator (also known as a dorsal column stimulator) delivers low voltage electrical stimulation to the tracts in the spinal cord to inhibit the transmission of pain signals to the brain. This, in turn, elicits a paresthesia in the corresponding dermatomes. The goal is to produce paresthesias that overlap the painful areas, so patients feel a mild tingling sensation where they used to feel pain. A percutaneous trial is performed in the outpatient setting. An epidural lead is placed using fluoroscopic guidance and this is connected to an external device. If the 3–10 day trial is successful, the lead is removed and the patient is scheduled for a permanent spinal cord stimulator implantation.