ABSTRACT: Pain due to malignancy can be controlled through simple means in most patients. In certain refractory cases, however, the chronic delivery of analgesics to the epidural or subarachnoid space may be appropriate. This review will discuss criteria for patient selection for neuraxial drug delivery, the technologic systems available for neuraxial drug delivery, and criteria for selection of the appropriate technology in the individual patient. [ONCOLOGY 13(Suppl 2):30-36, 1999]
A review of the various systems available for neuraxial infusion must be preceded by a very basic question: “When and in whom is it practical to use these neuraxial drug delivery systems?”
The majority of patients with cancer pain can be effectively treated with oral medication. The World Health Organization (WHO) analgesic ladder consists of a hierarchy of oral pharmacologic interventions designed to effectively treat pain of increasing magnitude. The WHO paradigm presents a framework for the rational use of oral medication before consideration is given to the application of other techniques of drug administration.
The Practice Guidelines for Cancer Pain Management from the American Society of Anesthesiologists provides an evidence-based paradigm for the use of neuraxial drug delivery systems (Figure 1). Oral medications should initially be used in the management of most types of cancer pain. When analgesia, with or without acceptable side effects, can no longer be achieved, or oral administration is no longer viable because of the presence of intolerable side effects or the inability of the patient to swallow or absorb medication, an alternate route of administration should be employed. Transdermal fentanyl(Drug information on fentanyl) may be used in patients with stable pain states who are either noncompliant with oral medications or unable to swallow or absorb medication. Subcutaneous or intravenous administration may be employed in patients with dynamic pain states who have a frequent need for “rescue” dosing for breakthrough pain, or in patients who are unable to swallow or absorb opioids and may benefit from a continuous infusion.
In general, neuraxial drug infusions should be considered when adequate analgesia cannot be achieved with systemic methods of drug delivery or when intolerable side effects occur. Neuraxial drug delivery should be used:
1.when severe pain cannot be con-trolled with systemic drugs because of dose-limiting toxicity;
2. when there is immediate need for a local anesthetic (some types of neuropathic pain);
3. after failed neuroablation; or
4. when patient preference indicates its use.
Similar to neuraxial drug delivery, neuroablative techniques should be considered when systemic therapies have failed to provide adequate analgesia or adverse effects are intolerable. Neuroablative techniques can be used early in the natural history of cancer pain in the presence of focal somatic lesions (eg, rib metastases) and in certain visceral (eg, pancreatic cancer) or neuropathic (eg, craniofacial) pain states. Neuroablation may be employed after failure of neuraxial drug administration, if appropriate.
Neuraxial drug delivery (neuroablative therapies, also) should not be used in unmotivated or noncompliant individuals, in persons who do not possess the prerequisite cognitive functioning to understand the risks and benefits, or when appropriate logistical systems do not exist.
Thus, use of neuraxial drug delivery systems does not merely imply the ability to perform sophisticated technologic procedures. Appropriate patients must be selected and resources and personnel must be available to respond to patients on an as-needed, around-the-clock basis. This implies the establishment of an office or network with professional support and integration of home care into the organizational construct for provision of care.
There are five types of neuraxial drug delivery systems (Table 1). Prior to understanding the criteria for selecting the appropriate drug delivery system and its respective advantages and disadvantages, it is necessary to become familiar with the technology of each system.
Percutaneous Catheter (Type 1)
In essence, percutaneous catheters are identical to the catheter systems used for continuous epidural anesthesia or continuous subarachnoid anesthesia during surgery and postoperative epidural analgesia. By definition, these catheters are designed for short-term use. They are made of nylon, polyurethane, or polyamide and can cause localized tissue reactions at the site of insertion. As in their use for postoperative analgesia, these catheters may potentially migrate into the subarachnoid or intravascular space (if placed epidurally). Extrapolating from the large postoperative experience, the incidence for both types of migration is about 0.2%.
Because these catheters are not designed for long-term use, mechanical problems appear over time: premature dislodgement from the epidural or subarachnoid space, catheter obstruction or kinking, and failure of the catheter adaptor/connector. All these factors combine to make this system suboptimal for truly protracted use.
Percutaneous Catheter With Subcutaneous Tunneling (Type 2)
Percutaneous catheters may be tunneled underneath the skin. Once again, the catheters used in this system are identical to those used for both intraoperative anesthesia and postoperative analgesia. It is assumed that tunneling reduces the incidence of dislodgement from the intended space for drug delivery.
Implanted Catheter With Subcutaneous Injection Site (Type 3)
The implantation of this type of delivery system (and the more technologically advanced neuraxial drug delivery systems) requires a minor surgical procedure and should therefore be performed only in a sterile environment. Fluoroscopy is essential for verifying proper placement of the catheter tip. Irrespective of intended epidural or subarachnoid placement, the needle is best inserted using a paramedian approach. Such an approach obviates the sharp angulation created by the midline approach.
Using local infiltration analgesia, a paravertebral incision is then made around the needle entrance site with the needle in place to avoid laceration of the catheter. A catheter exit site or port site is then chosen, and appropriate tunneling of the catheter(s) is performed.
Theoretically, epidural catheter insertion may be as high as the end of the epidural space at the level of the foramen magnum. Subarachnoid catheters are easier to thread over long distances and have even been placed intracisternally. At minimum, both epidural and subarachnoid catheters should be advanced at least two vertebral levels above the point of insertion, thereby allowing for inadvertent withdrawal of the catheter during the remainder of the procedure. Fluoroscopy with contrast injection is used to verify proper epidural or subarachnoid placement.
There are two design types for implanted catheters with subcutaneous injection sites: 1) implanted but exteriorized catheters (in contradistinction to merely tunneled catheters) and 2) subcutaneous ports with completely internalized catheters.
The DuPen silicone-rubber catheter (CR Bard, Inc., Salt Lake City, UT) is of the implanted exteriorized type (Figure 2). This is a dual catheter system with insertion of a distal, smaller diameter catheter into the epidural space, tunneling of a larger proximal catheter from the exit site to the back, and connection of the catheters. The proximal catheter is exteriorized and connected to an adaptor for injection or continuous infusion.
The catheter design is notable for the presence of a Dacron cuff positioned approximately 5 cm internal to the catheter exit site. Epithelization of the cuff theoretically reduces the risk of catheter dislodgment. Patient-controlled analgesia is achieved by connection to an external, appropriately programmed infusion device.
The second type of implanted catheter system with a subcutaneous injection site is a portal system (eg, Port-a-Cath, Pharmacia-Deltec, Inc., St. Paul, MN) (Figure 3).  This is a totally internalized system. The stainless steel port contains a 60-m screen filter that is connected to the catheter. The catheter is inserted in the epidural space, using essentially the same technique as described previously. The catheter is tunneled from the back to the site for the port pocket.
The port pocket is created in subcutaneous tissue in an area that is supported by bone, usually a rib, so as to facilitate needle insertion. The rib gives firm support to the port (ie, a “back-stop” mechanism). The pocket is created with a 1-cm layer of subcutaneous fat above the port and the port is then sutured to the fascia to prevent inversion.
To administer medication, the port must be accessed. A noncoring needle must be used to allow repeated access to the port and prevent damage to the septum. Patient-controlled analgesia or continuous infusions are possible by continuous access and connection to an external, appropriately programmed infusion device.