Pump selection

Two major classes of implanted pumps have been designed for intrathecal infusion therapy. Constant flow pumps rely on a fairly constant pressure exerted by a gas on a diaphragm, forcing a constant stream of medication from the reservoir through a small orifice. Programmable pumps are extremely accurate and reliable. Any infusion rate within the volume capabilities of the pump may be programmed. In addition, complex continuous infusions with a daily bolus and/or varying infusion rates throughout the day may be programmed.

Indications

Patient selection for continuous intrathecal morphine therapy is not as well defined as for spinal cord stimulation. Most candidates are patients with intractable pain conditions that have failed to respond to conservative therapies and have failed chronic opioid therapy due to either excessive side effects and/or inadequate analgesia. Candidates should have a life expectancy of at least 3 months before an implantable pump is considered. There are no other simple rules for choosing appropriate candidates. Nearly all patients will receive substantial relief from a test dose or infusion trial. Many will develop significant tolerance to intrathecal opioids after 1–2 years of infusion therapy such that pain relief is only mildly improved from pre-implant levels.

Choosing patients for intrathecal baclofen therapy is much more straightforward than selection for intrathecal morphine therapy. Patients with spasticity of central origin who have failed oral baclofen therapy and at least one other appropriate antispasmodic agent are suitable candidates. The types of patients vary from those who will be able to ambulate more easily if the therapy is successful to those who will remain bedridden but will be easier to care for.

Patients are generally referred by a neurologist or neurosurgeon for an intrathecal baclofen trial. Single shot intrathecal test doses are given in a monitored setting where the patient’s response to the injection can be observed on an hourly basis for 8 hours. Response may be rated with the Ashworth scale and by observing functional ability. Some patients rely on the spasticity of certain muscle groups for ambulation and arm movement. Function in these cases may worsen as spasticity improves. Test dosing begins at 50 μg. Doses of 75 μg, and 100 μg may be given on subsequent days if the initial dose produces no results. If the patient does not respond to a 100 μg test dose, implantation is not a viable option.

Patient selection

Patient selection is the most important part of the pre-implant process. Experience indicates that a structured approach to the pre-implant phase facilitates the best possible experience for patient and practitioner. The clinician should establish a checklist algorithm to ensure that each patient has experienced a complete pre-implantation evaluation. Careful selection of patients improves outcome results and builds trust in the patient–clinician relationship.

Important components of the pre-implantation checklist include determining if the patient meets appropriate criteria. Appropriate criteria include:

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  Ineffective oral analgesia with multiple oral or transcutaneous trials including dose titrations

  
  
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  Intolerable side effects despite adequate rotation of opioids

  
  
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  Intractable spasticity unrelieved by oral antispasmodics with improved Ashworth scores at baclofen test dose

  
  
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  Access to care

  
  
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  Functional analgesia during temporary trial infusion

  
  
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  Psychological stability and realistic post-implant goals

  
  
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  Patient acceptance.

An appropriate pre-implant checklist includes:

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  Does the patient meet appropriate patient selection criteria?

  
  
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  Has the patient been cleared by a knowledgeable psychologist?

  
  
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  Did the patient achieve a 50% or greater reduction in pain during the trial infusion?

  
  
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  Did the patient have appropriate occupational and physical therapy evaluations during the trial that showed acceptable functional gains?

  
  
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  Did the patient have preoperative teaching?

  
  
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  Was the infection risk assessment completed and discussed with the patient and family?

The patient must be physically able to have the pump and catheter implanted. In some cases, the patient may have had very extensive spinal or abdominal surgery which can increase the level of surgical complexity. The patient must be evaluated for access to the intrathecal or epidural space, and access to a site suitable for pump implantation. Patient positioning may be an issue secondary to anatomical factors. The patient will need to be placed in the lateral decubitus position with the pump side up during the implant procedure.

The risk of intraspinal catheters and pump implantation should not be ignored. The risks are manageable and, in experienced hands, are limited. General risks include infection, post-dural puncture headache, catheter-related epidural infections, granuloma formation, dose escalation and tolerance, and serious withdrawal symptoms due to pump or catheter failure (clonidine and baclofen).

Introduction

An intrathecal pump system is implanted via a sterile surgical procedure performed under local, regional, or general anesthesia. The implant procedure typically lasts from 2 to 4 hours. Prior to the procedure, a complete preoperative physical examination should be performed and the patient should be educated as to the procedure and the associated risks.

Preoperative preparation

Before the implantation procedure, the physician and patient need to spend some time deciding on the side and location of the pump. It is usually placed in the left or right lower quadrant of the abdomen. It is placed so that it does not contact the iliac crest, pubic symphysis, ilioinguinal ligament, or the costal margin.

Preoperative antibiotics are given in the holding area. Usually, a cephalosporin is adequate and should be completely infused prior to the patient’s transportation to the operating suite.

Anesthesia

Implantation of the catheter and subsequent pump placement may take place with the patient under general or local anesthesia with monitoring. Local anesthesia, in conjunction with sedation, is often preferred in the outpatient setting. When general anesthesia is chosen, the use of muscle relaxants is usually avoided until after the catheter is passed into the intrathecal space.

Procedure

Adverse events

Adverse events of intrathecal therapy are classified as either system related or catheter related. System-related complications include cessation of therapy due to end of service life or component failure of the pump, change in flow performance or characteristics due to component failure, inability to program the device due to programmer failure or loss of telemetry, and catheter access failure due to component failure.

Catheter-related complications include, but are not limited to, changes in catheter performance due to catheter kinking, catheter breakage, complete or partial occlusion, catheter dislodgement or migration, or catheter fibrosis or hygroma. Hygroma can be difficult to diagnose and is sometimes confused with seroma or hematoma. Careful fluid analysis may give insight to the origin of the problem but, in some situations, the mixture of CSF with blood or serum makes the diagnosis difficult and a surgical exploration is needed to confirm the diagnosis.

Testing for therapy failure includes careful attention to end volume to computer predicted volume at pump refill, plain films of the catheter and pump, contrast studies of the catheter using the side access port, and rotor testing by x-ray analysis. Nuclear medicine studies of the pump using labeled xenon and other agents have been described but are not practical for clinical use.

Conclusions

The placement of the spinal needle for implantation of an intrathecal pump is the most critical step of the procedure and is also the step with the highest risk of neuronal injury. It is a skill that needs to be mastered if the implanting surgeon is to become comfortable with the therapy. Proper positioning, fluoroscopic guidance, and a paramedian approach with a shallow needle angle, all add up to a successful procedure and outcome.

The decision to use a spinal drug delivery system should build on the previous aggressive and optimized use of more conservative modalities. The patient’s pain-related diagnosis, other medical diagnoses or general health, previous treatment, and future potential treatment options are all considered in the process of evaluating the patient for spinal drug delivery. There are many advantages to spinal drug delivery. Intrathecal opioid doses of 300 times the dose of oral morphine can be achieved. Clinicians have the choice of programmable or cost-effective, non-programmable pumps. The systems are completely implantable and are capable of combinations of simple infusions to a complex infusion pattern. The clinician also has the ability to add adjuvant drugs, resulting in decreased opioid requirements. The amount of drug delivered is precise and there is the future ability to deliver patient controlled analgesia (PCA) doses through the intrathecal space.

Introduction

Like intrathecal infusion trials, patient selection for trialing of spinal cord stimulation is essential to achieving a good outcome with permanent implantation. Trials can be informative to both the physician and patient and provide a significant amount of information about potential success of stimulation, location of electrodes, array design and type of generator required. The ultimate goal of the procedure will be to relieve pain by applying electrical stimulation to cause paresthesias covering and overlapping the areas of pain. The stimulation should not be painful and there should be no motor effects. Stimulation will not affect acute pain. Spinal cord stimulation is a reversible mode of neuromodulation that impairs vibratory sensation. It is necessary to perform a trial of sufficient length to forecast long-term success and identify a failure. A trial of 5–7 days is generally sufficient to provide the needed information while reducing the infection risk.

Preoperative considerations

It is important to conduct a subjective review of an individual patient’s functional, cognitive, and behavioral status. The patient needs to be able to tolerate the prone position. A complete discussion of common complications and informed consent needs to take place. Patients need to be aware of the potential for post-dural puncture headaches (1% risk of dural puncture), dural insult with the needle or lead, potential epidural blood patch, infection, bleeding, neurologic injury due to nerve or spinal cord trauma, inability to access the epidural space, and intolerance to the paresthesia. Patients need to be instructed on the trial process and be comfortable with the hardware and use of the equipment and the family needs to be present for the teaching. Patients need to sign a list of postoperative instructions.

Patients should be evaluated for the presence of coexisting diseases. Careful consideration should be given to morbid obesity, diabetes mellitus, coagulopathy, single lead pacemaker or pacemaker/defibrillator, and smoking.

SCS patient selection

Patient selection will be essential to developing a successful neuromodulation practice and increased patient satisfaction. Patients need to be evaluated for various factors. They need to have a chronic painful condition that has affected their daily life and their ability to maintain employment. They should have failed conservative (non-operative) management and, if mechanical pain exists, it should not be surgically correctable. The patient should be readily acceptable of the procedure and be fully cooperative and have the physical ability to manage the SCS system. The patient also needs to have a psychological evaluation by a trained therapist. Appropriate diagnostic studies prior to considering a SCS trial may include MRI or CT imaging, EMG, etc. If at all possible, an MRI is preferable. It is not generally necessary that a thoracic MRI is needed prior to a percutaneous trial, but if a laminectomy trial paddle lead is planned, a preoperative thoracic MRI is essential. The MRI and imaging studies will allow a correlation of the primary complaint to pathology seen on the imaging studies. The physician should be aware of multifocal pain complaints and all treatable/correctable pathology ruled out. The patient should have failed all conservative and other interventional therapies, and verification that this chronic condition has had a significant impact of pain on the patient’s quality of life and activities of daily living.

SCS psychological clearance

Every patient will need a complete psychological evaluation prior to proceeding with a trial of stimulation. This will necessitate a referral to a therapist and at least one complete therapy session. The psychologist will need to ensure that there are no acute contraindications to therapy, such as an acute psychosis, personality disorder, or untreated depression. There can be no active history of drug or alcohol abuse or illicit drug use. It should be part of the physician evaluation that the patient’s pain complaints are felt to be real and related to diagnosis and that the patient understands, in general terms, the procedure (risks/benefits), and that they have reasonable expectations/motivation. It may be appropriate that in-office testing can be performed if the patient is well known to the office and a full evaluation is not felt to be necessary.

Percutaneous versus tunneled trial leads

A patient may undergo two types of trials. It is usually the implanting physician who decides whether the trial leads will be purely percutaneous or tunneled laterally to a stab wound and this decision is made prior to the trial. A percutaneous trial is a temporary trial as opposed to a tunneled or permanent trial. A permanent lead requires that it be performed in an operating room, whereas a temporary lead may be performed in an office-based fluoroscopy suite.

With a percutaneous trial, the leads are placed thru an epidural needle and advanced to the appropriate level. They are then connected to an external battery source and intraoperative testing is performed and the patient is brought to the recovery room for final testing. The trial typically lasts 5–7 days and, at the end of the trial, the temporary leads are removed and discarded. At that time, a detailed discussion takes place between patient and physician and results of the trial are evaluated and, if successful, a permanent implantation is scheduled.

With tunneled trial leads, implantation must be performed in an operating room. After successful placement of the leads and adequate intraoperative testing, the leads are sutured to the paraspinal or supraspinous ligament and are coiled into a midline incision with adequate undermining to allow a restraining loop to be coiled without any undue tension. They are connected to an extenson and the extension is tunneled to a lateral stab incision at the opposite side of the planned generator pocket. After a trial lasting 3–7 days, the patient returns to the operating room and will either have the leads removed surgically or the extension will be removed and the leads will be tunneled to the newly created generator pocket.

When comparing the two techniques, it becomes obvious that percutaneous trials are less invasive requiring only needle insertion, while tunneled trials involve a surgical incision with the associated discomfort. The discomfort associated with a tunneled trial may require a longer trial or may cloud the evaluation of the patient’s level or percentage of pain relief. This less invasive technique seems to be easier to obtain consent and patients tend to be more accepting of this procedure. They have already undergone many epidural injections and they have an understanding that the stimulator lead placement is similar to an injection with the exception that a ‘wire’ will be left in place for 5–7 days. If, during the trial, it is determined that a different location is required for permanent implant, it tends to be easier to alter the planned implant with a percutaneous trial.

If difficult anatomy is anticipated or encountered, a tunneled trial should always be considered. It may be necessary to include a tunneled trial in the operative consent with potentially difficult patients. There is a perceived increased risk of infection with a tunneled trial due to reopening the midline incision and allowing bacteria to enter thru the incision and also thru the extension site. In the USA, percutaneous trials are the more commonly performed trial.

Trial evaluation

There are generally accepted criteria for what constitutes a successful trial. The patient should have obtained greater than 50% pain reduction from preoperative levels. This can be measured on a visual analog scale or by the perceived percentage reduction. Studies show that if a patient obtains greater than 70% relief, there is a better chance of long-term efficacy and success.

It is important to include functional improvement in the evaluation of the success of trial stimulation. It is important that specific milestones are discussed in the preoperative visit and that they are documented prior to the trial. Then, during removal of temporary leads, it is important to evaluate whether these functional milestones were met. These milestones can be something as basic as walking in the mall, sitting thru a meal at a restaurant, playing golf, or going to the movies. It is important to include family members, spouses or siblings in the evaluation. Once the evaluation is completed, the decision is made whether or not to proceed to implantation.

Operative technique

Conclusions

The criterion by which the trial period is deemed a ‘success’ or a ‘failure’ has historically been a reduction of pain by 50%. In addition to the overwhelming painful sensations, chronic pain affects many aspects of a patient’s life – psychological function, physical function, self-care, social interactions, and work status. Many physicians now consider improvements in activity, quality of life, and analgesic consumption during the trial just as predictive of favorable long-term outcomes as pain relief. Fifty percent pain reduction alone may inadequately describe the impact of the therapy. The pain should be neuropathic in nature. It is also important to ensure that the patient is not forced to fit a pain syndrome. Do not pressure the patient to accept the implant if the patient says that ‘maybe I felt good’ or if the patient had problems with the trial controller. One size does not fit every patient. It is important to design the correct system for the patient. Following a successful trial, the patient is brought back to surgery for the implant procedure. As a safety check – check stimulation, if only briefly, in the recovery room, especially with percutaneous leads. You will want to verify that the electrode did not move and that paresthesia is the same as it was in the operating room/procedure room. If the coverage is inadequate, the patient can be returned to the operating/ procedure room and the lead can be repositioned. Transferring the patient from the operating room/procedure table to the stretcher is a common cause of lead migration, especially if the patient has been positioned on a surgical frame. The highest risk for bleeding in the epidural space is in the first 24 hours. Patients should be monitored for changes in neurological function. A patient who complains of continuous paresthesia when the device is not activated should be evaluated immediately. Patients with epidural hematomas will complain of numbness and severe back or leg pain followed by weakness. This requires immediate neurological evaluation.