Anatomy and Physiology of Pain Principles of Pain Spinal Cord Stimulation Intrathecal Drug Delivery Selective Spinal Cord Lesioning Neuroanesthesia

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The overall implantation procedure for a neurostimulation system generally involves three stages:
● Lead placement and intraoperative test stimulation
● Screening test period
● Complete system implantation with either the totally implantable system or the radio frequency system (if the screening test has been successful)


Preoperative set up
Selecting the leads
Selecting the appropriate leads is essential for successful neurostimulation. The process of lead selection is based on patient information (chronology and symptomatology of pain), the physicians diagnosis of the patient’s pain type and pattern e.g. simple pain or complex pain, and physician preference. Two basic types of neurostimulation leads can be used with neurostimulators:
● Percutaneous leads – Leads that are inserted through a needle into the epidural space
● Surgical leads – leads that are implanted via a laminectomy
Percutaneous leads have become increasingly popular because the implantation procedure is substantially less invasive. However, it is generally accepted that surgical leads should be used when repeated migrations occur or when the voltage required for paraesthesia is high.
Selecting the implant site
The table below summarizes optimal lead sites by vertebral body and pain location. It is important to note that when the back is stimulated so are the legs. For percutaneous leads the entry level is 1–2 vertebral bodies below the target vertebra. For surgical leads, the incision is usually made half a vertebrae below (or at the bottom of) the target vertebra.

Table 1: Optimal lead sites by vertebrae and pain location
Pain location Lead tip level
Foot only T12–L1
Lower leg and ankle T11–T12
Knee and thigh T9–T10
Thigh T9–T10
Buttocks T9
Lower back and lower limb T8–T9
Upper chest wall/Precordium T1–T2
Upper extremity/Upper Limb  C3–C5


Initial lead placement
The protocol for initial lead placement is based on lead type. A summary of two common techniques used for percutaneous and surgical leads, respectively, is highlighted below.
Percutaneous leads
Prior to beginning initial lead placement, the physician uses fluoroscopy to mark the insertion or entry level for the lead(s). Lead placement is performed under local anesthesia within the sterile field. All the accessories necessary for placement are provided in a lead kit. If two leads are used, two lead kits are required. The physician will begin the initial lead placement procedure by:
● Identifying the vertebral body using fluoroscopy and administering an anesthetic along the incision line (Figure 1)








● Using a long needle to provide a marker at the midbody of T10 to provide a constant point of reference (Figure 2)
● Making a small puncture wound and inserting the Tuohy needle under fluoroscopic guidance (Figure 3)
● Introducing the lead and threading it to the target vertebra (Figure-4)
● Attaching the screening cable to the proximal end of the lead when the lead is in place (Figure 4 and 5)
At this point the physician will pass the end of the screening cable out of the sterile field to the nurse. With the screener off, the nurse will connect the cable to the screener (temporary power source) and intraoperative test stimulation will begin (Figure 6).


Surgical leads
Surgical lead placement is usually performed under general anesthesia, though sometimes under local anesthesia, within the sterile field. The physician will begin the lead placement procedure by:
● Identifying the vertebral body using fluoroscopy and administering an anesthetic along the incision site.
● Making the skin incision and then using electrocautery to expose the interlaminar space (Figure-7)
● Completing the laminectomy by exposing the dura matter (Figure-8)
● Introducing the lead blank and then passing the lead through the ligament window (Figure-8 and 9)
● Passing the lead cephalad (towards the head) until optimal position is achieved (Figure 10)
● At this point the physician will pass the end of the screening cable out of the sterile field to the nurse. With the screener off, the nurse will connect the cable to the screener (temporary power source) and intraoperative test stimulation will begin. There are two different types of temporary screener, one for the single lead and one for the dual lead (Figure 11)






Intraoperative test stimulation
The purpose of intraoperative test stimulation is to create an appropriate field of paresthesia to cover the patient’s pain pattern. The location and strength of the paresthesia are optimized by manipulating:
● Lead position along the length of the
patient’s spinal cord
● Stimulation parameters (amplitude, pulse width and rate)
● Lead electrode selection (i.e. changing the location and number of anodes and cathodes on the lead).

Screening test period
The basic screening protocol, which should be followed in every diagnostic test stimulation procedure, is carried out as follows:
● The screener is turned on and the amplitude is set to 0 V, the pulse width to 210 msec and the rate to 40 Hz
● To start, the centre bipole electrode selection should always be used. Center bipole consists of one positive electrode and one negative electrode on each lead (Figure 12)
● The amplitude is increased to the point where the patient begins to feel a tingling sensation
● The amplitude is increased until the patient’s pain threshold (intensity of a noxious stimuli necessary for a person to perceive pain) is reached
● The amplitude is reduced to the point where the patient feels comfortable, yet strong, paresthesia
● Microadjustments in lead position are made until the optimal lead position is located (trolling)
● The pulse width is gradually adjusted until it covers the breadth of the patient’s pain. Some patients with back and leg pain may require a pulse width higher than 330 μs
● At the end of the screening period, all system settings are carefully documented. Normally, amplitude and pulse width are usually the only parameters adjusted during intraoperative test stimulation. The rate should remain at 40 Hz.

Figure-12: Center Bipole electrode selection.

Patient evaluation
Patient evaluation, which occurs between diagnostic test stimulation procedure and complete system implant, may last from a day to several weeks. During patient evaluation, patients receive a screener with which to adjust (within a clinician-defined range) the stimulation parameters established during intraoperative test stimulation. Patients should fully test the neurostimulation system under their normal, day-to-day activities, such as walking, sitting and working. Patients are encouraged to try different amplitudes to determine optimal device settings. Some centers encourage patients to document the setting after each use along with the duration of the stimulation and time of day. The screening test period is also an opportunity for the patient to develop an understanding of the technology and realistic expectations of the therapy.
Patient evaluation allows the physician and the patient to:
● Evaluate the impact of stimulation on the patient’s pain and daily life
● Optimize settings for the best pain relief
● Identify the patient’s energy requirements
● Determine whether the patient is comfortable both with the operating system and with the feeling of paresthesia
If the patient does not respond positively to neurostimulation during the screening test period, the lead is removed and the patient is often referred for an intrathecal drug delivery trial. However, if the patient experiences pain relief of at least 50% during test stimulation, the physician and the patient may agree to proceed with the implantation of a complete system.

Complete system implant
If the diagnostic test stimulation procedure was successful, a complete system can be implanted. Neurostimulator selection is based on initial stimulation parameters, patient evaluation data and lead requirements.
Complete system implant is usually scheduled two weeks after the diagnostic test stimulation procedure to provide the patient with ample time to evaluate neurostimulation and to reduce the likelihood of infection.
Possible implant sites include the upper abdominal wall, the upper buttocks, or a subclavicular (below the collar bone) pocket. The choice of implant site is determined by patient and physician preference. The most common site is the upper abdominal wall (Figure 13–16).





Programming stimulation parameters
Stimulation parameters are programmed according to patient evaluation data and the parameters determined during intraoperative test stimulation. There are two considerations with respect to device programming:
● Maximizing patient comfort
● Extending battery life (e.g. rates greater than 50 Hz substantially shorten battery life)
In order to extend battery life, some neurostimulators can be programmed to cycle. Cycling means that the device can be programmed to turn on and off for specified periods of time.

Postoperative management
Once the neurostimulation system is implanted, patients are closely monitored. Postoperative care involves:
● Management of complications
● Patient education
● Care of the operative site

Management of complications
Potential postoperative complications include:
● Surgical complications
● System complications
Surgical complications
Patients who have poor nutritional status, are small in build and/or thin, or who have generally poor health are at greater risk for post-surgical infections. Potential surgical complications include:
● Infection
● Hematoma
● Epidural hemorrhage
● CSF leakage
● Pain and discomfort
● Seroma at the neurostimulator or receiver site
System complications
Complications with a neurostimulator system may occur and include:
● Battery failure and/or battery leakage
● Lead and/or neurostimulator erosion or migration
● Connection problem
● Wire breakage
● Short circuit
In addition, the patient may experience:
● Loss of pain relief
● Loss of stimulation
● Undesirable change in stimulation described by some patients as uncomfortable ‘jolting’ or ‘shocking’
● Radicular chest wall stimulation
● Allergic or immune system response to the implanted materials
During the postoperative period, patients are advised to limit their activities to reduce the risk of lead movement and subsequent loss of stimulation effectiveness. Postimplant instructions are listed in the table below.

Table 2: Postimplant instructions for SCS patients

To help reduce lead movement and subsequent loss of stimulation, patients must follow the activity precautions listed below.

Immediately after surgery ● Patients should stay in bed for 10 to 12 hours or according to their physicians instructions. Bed rest reduces the risk of lead movement
● Patients should raise the head of their bed by around 20 degrees for the first postoperative night to support their spine
The day after surgery ● Patients should walk for brief periods to build up their physical strength, keeping their back as straight as possible to prevent lead movement
For 6 to 8 weeks after surgery PATIENTS SHOULD NOT:
● Put their arms over their head
● Bend, twist, stretch or lift more than 2.5kg
● Sleep on their stomach
● Climb too many stairs
● Sit too long in a chair
● Drive for several weeks to reduce the risk of abrupt movements or shifts in position which will increase the risk of lead movement
● Operate motor vehicles, power tolls or equipment while the stimulator is on.
● Sleep with a firm mattress
● Resume showering and bathing
● Follow their physician’s recommendations regarding sexual activity
● Obtain approval from their physician before having their spine manipulated by a chiropractor or other physician
● Move the upper part of their trunk as one i.e. the head should not be turned without also turning the hips
● Build up their physical strength by walking for brief periods of time each day or engaging in a physical therapy program according to their physicians instructions

As well as the above postimplant instructions, there are also many ongoing instructions and precautions that all patients should follow. These differ depending on whether the patient has received an IPG system or an RF system. Special instructions and precautions for both systems are shown in tables 3 and 4.


Table 3: Special instructions and precautions for patients with a battery (IPG) system

For patients with control magnets:
● The control magnet should be kept away from the implanted battery when it is not being used to turn the stimulator on or off. This is because the magnet may turn the neurostimulator on or off.
For patients with patient programmers:
● Patients should exercise caution when increasing amplitude to avoid unpleasant stimulation e.g. ‘shocking’ or ‘jolting’. Patients should always start at the lowest amplitude and then slowly increase
● The programmer and its accessories should be cleaned with a damp sponge or cloth moistened with water, mild detergent or alcohol. Patients should not allow excessive moisture into the programmer
● If patients use the optional antenna with their programmer, they should follow the skin care instructions outlined for the RF-transmitter antenna
To avoid damaging the programmer patients should not:
● Immerse the programmer into any liquid
● Clean the programmer with aggressive cleaning agents such as paint thinners, turpentine or nail polish remover


Table 4: Special instructions and precautions for patients with an RF system

Care of the skin around the RF transmitter antenna:
● To reduce the risk of skin irritation in the area of the antenna, patients should keep the skin in that area clean, dry and free of pressure
● Patients should inspect the skin area daily where they place their antenna to ensure that it is healthy. If there is any swelling or redness in the area, patients should contact their physician before using the antenna again
● Each day patients should clean the skin over the receiver with an antibacterial soap and change the antenna attachment discs.
Care of the RF transmitter and antenna:
● Each week patients should clean the outer surface of their transmitter using a cloth dampened, but not saturated, with mild soap and water. Never dip the transmitter in cleaning solution
● Every day, patients should wash their antenna with mild soap and water. Before cleaning, the antenna should be disconnected from the transmitter. The antenna should be rinsed thoroughly to eliminate any soap. Patients must be careful to avoid getting the metal connector end of the cord wet. The antenna should be dried with a clean towel immediately after washing. When not in use the antenna should be stored in a plastic bag to protect it from dust
● Patients must replace the battery when the BAT indicator appears on the display, if they suspect weak batteries, or if they do not get adequate pain relief from the highest amplitude setting. To prevent corroding the electronic components, patients must not leave depleted batteries in the transmitter
● The transmitter should be stored at room temperature. Extremes of hot and cold or direct sunlight should be avoided. If the transmitter is stored for more than a month, the 9 V battery should be removed

What’s Up
Inomed ISIS Intraoperative neurophysiological monitoring started to function in all our related surgeries.
Oct /07/2009
The author celebrating 30 years experience in neurosurgery.
Skyra 3 tesla magnetom with all clinical applications  are running in the neurosuite.
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