Intrathecal Catheter Implantation

50 Intrathecal Catheter Implantation



James P. Rathmell



Perspective


After thousands of years of empiric use of opioids for treating pain, in the early 1970s a class of highly specific opioid receptors was identified. Soon thereafter, opioid receptors were localized in the brain and spinal cord. Investigators developed a model of chronic catheterization of the spinal subarachnoid space in experimental animals, and evidence that direct application of morphine at the spinal cord level produces selective spinal analgesia soon followed. Based on this limited experimental evidence, intrathecal morphine was administered to patients with severe pain associated with advanced cancer, and it produced profound and long-lasting pain reduction.


Since these first bold clinical experiments, we have witnessed a rapid transition from the laboratory to clinical practice. Intrathecal morphine and other opioids are now widely used as adjuncts in the treatment of acute and chronic pain, and a number of agents show promise as analgesic agents with spinal selectivity. Continuous delivery of analgesic agents at the spinal level can be carried out using percutaneous epidural or intrathecal catheters, but vulnerability to infection and the cost of external systems typically limits them to short-term use, in most cases less than 6 weeks. Reliable implanted drug delivery systems that make long-term delivery of medications to the intrathecal space feasible are available. These systems consist of a drug reservoir/pump implanted in the subcutaneous tissue of the abdominal wall that is refilled periodically through an access port. The pump may be a fixed-rate, constant-flow device or a variable-rate pump that can be programmed using a wireless radiofrequency transmitter, similar to the programming possible with implanted cardiac pacemakers.


Patient selection for spinal pain therapy is empiric and remains the subject of some debate. In general, intrathecal drug delivery is reserved for patients with severe pain that does not respond to conservative treatment. Most patients with cancer-related pain have ongoing pain despite appropriate oral opioid therapy, or they may have developed intolerable side effects related to these medications. Randomized controlled trials comparing maximal medical therapy with intrathecal drug delivery for cancer-related pain have demonstrated improved pain control and reduced opioid-related side effects with intrathecal pain therapy. Intrathecal drug delivery has also been widely used for noncancer pain, particularly for the treatment of chronic low-back pain. Use of this therapy for noncancer pain, however, has not been subject to controlled trials and remains controversial.


Once a patient is selected for intrathecal therapy, a trial is carried out. Most physicians now conduct trials by placing a temporary percutaneous intrathecal catheter and infusing the analgesic agent over several days to judge the effectiveness of this therapy before a permanent system is implanted. Some carry out the trial of intrathecal therapy using a single dose or a continuous epidural infusion. The most common analgesic agent used for spinal delivery is morphine, which remains the only opioid approved for intrathecal use by the U.S. Food and Drug Administration.



Placement




Anatomy


The intrathecal catheter is placed directly in the cerebrospinal fluid (CSF) of the lumbar cistern by advancing a needle between the vertebral laminae at the L2-L3 level or below. Direct delivery of the opioid at the spinal level corresponding to the dermatome(s) in which the patient is experiencing pain may improve analgesia, particularly when local anesthetics or lipophilic opioids (e.g., fentanyl or sufentanil) are used. Thus, some practitioners have advocated threading the catheter cephalad to the appropriate dermatome. In recent years, there have been some reports of granuloma formation surrounding the tip of some chronic indwelling intrathecal catheters. These inflammatory masses often present with sudden neurologic deterioration caused by spinal cord compression. Many physicians now recommend that implanted intrathecal catheters be placed only within the lumbar cistern below the conus medullaris (at about L2), where the appearance of an inflammatory mass is less likely to impinge directly on the spinal cord.



Position


Before the procedure, discuss with the patient the location of the pocket for the intrathecal pump. Most devices are large, and the only region suitable for placement is the left or right lower quadrant of the abdomen. Once the site is determined, the proposed skin incision is marked with a permanent marker while the patient is in the sitting position. The position of the pocket on the abdominal wall is deceptively difficult to determine once the patient is lying on his or her side. If the location is not marked, the pocket is often placed too far laterally in the abdominal wall.


Implantation of an intrathecal drug delivery system is a minor surgical procedure that is carried out in the operating room using aseptic precautions, including skin preparation, sterile draping, and full surgical attire (Fig. 50-1A). The procedure can be conducted under regional anesthesia or general anesthesia using dedicated anesthesia personnel. Performing the initial spinal catheter placement under general anesthesia is controversial, and concerns about neural injury are similar to those when performing any neuraxial technique under general anesthesia.


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Figure 50-1. Intrathecal drug delivery system implantation. A, View of a typical operating room arrangement during intrathecal implantation. The patient is placed in the lateral position with the fluoroscopic C-arm in place for a cross-table anteroposterior view of the lumbar spine. B, Initial spinal needle placement at the L3-L4 interspace using a paramedian approach. Free flow of cerebrospinal fluid (CSF) indicates an intrathecal location. C, Intrathecal catheter placement through the spinal needle under fluoroscopic guidance. Anteroposterior (D) and lateral (E) radiographs of the intrathecal catheter tip in good position, with the tip adjacent to the L2-L3 intervertebral disk. F, After confirming the final position of the catheter tip, the proximal portion of the catheter is fastened to the surgical field and the spinal needle is withdrawn about 1 cm to lie in the subcutaneous tissue. Leaving the needle in place protects the catheter during subsequent dissection. G, A cephalocaudad incision is made through the skin and subcutaneous tissues; the incision extends above and below the needle entry point. H, Using blunt dissection, the skin and subcutaneous tissues are further divided until the lumbar paravertebral fascia is exposed. I, A pursestring suture is placed around the base of the needle in the paravertebral fascia; this suture reduces the likelihood that CSF will track back along the catheter and result in a subcutaneous CSF collection. J, The needle and catheter stylet are removed together while the catheter is held firmly in position. K, The catheter is secured to the paravertebral fascia using an anchoring device provided by the manufacturer. L,

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May 31, 2016 | Posted by in ANESTHESIA | Comments Off on Intrathecal Catheter Implantation

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