Invasive Therapy

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Invasive therapies should be considered when pain continues despite adequate doses of appropriate analgesics or when side effects become intolerable. Nerve blocking techniques, neurolytic techniques, parenteral infusions, and implantation technologies improve overall quality of life and become cost-effective when less-invasive therapies fail to produce adequate analgesia.45

Regional and Peripheral Nerve Blocks

Nerve blocks may provide diagnostic information about the causes of the pain or may allow time for another anticancer therapy to have effect. Analgesia will be of limited duration although it frequently outlasts the pharmacologic duration of the local anesthetic agent. If a somatic nerve is to be blocked with a local anesthetic agent, it should be done proximally to the locus of pain generation in order to diminish afferent impulses. As it is difficult to spare the sensory and motor fibers, the patient will experience numbness and weakness in the distribution of that nerve.

Sympathetic Ganglion Block

Sympathetic plexus or ganglion blocks are indicated if pain is predominantly visceral.46 Blocks of the superior hypogastric plexus are intended to relieve pelvic pain due to malignancy or radiation-induced cystitis or enteritis.4748 A network of sympathetic nerves lies anterior to the fifth lumbar vertebral body (Figure 26-2). At that level, it is a retroperitoneal bilateral structure that innervates the pelvic viscera via the hypogastric nerves. The block is performed with the patient in the prone position, and needles are inserted 5 to 7 cm from the midline bilaterally at the level of the L4-L5 spinous interspace. The needles are directed under computed tomography (CT) or fluoroscopic guidance until they reach the position of the plexus (see Figure 26-2, B). A diagnostic or prognostic block can be performed with 6 to 8 mL of 0.25% bupivacaine whereas injection of a neurolytic agent such as alcohol or phenol will give a prolonged block. The sacrococcygeal plexus or ganglion impar can also be blocked by a posterior rectal or transsacrococcygeal approach to relieve rectal and perineal pain. Adverse effects, most of which are usually transient, include neuritis, weakness, hypotension, and bladder or bowel dysfunction.

Celiac plexus blocks have been advocated for pain relief in patients with abdominal malignancies. When germ cell tumors metastasize to para-aortic nodes or as the tumor volume increases, patients may experience increasing abdominal pain. The celiac plexus lies anterior to the aorta, at the level of the junction of the twelfth thoracic (T12) and first lum

Celiac Ganglion Level

bar (L1) vertebral bodies, and is responsible for the transmission of pain impulses from the abdominal viscera (see Figure 26-2). Several approaches to this plexus have been described for neurolysis, depending on the target space where the alcohol or phenol is to be injected.49 These approaches include posterolateral, transdiscal, and anterior approaches, done with CT or fluoroscopic guidance. Figure 26-3 shows the posterolateral approach to the celiac plexus under CT guidance, with needles placed bilaterally. Verification of needle placement close to the celiac plexus is made with the injection of radiopaque dye. Blockade of the splanchnic nerves with radiofrequency neurolysis has also been described50 (see Figure 26-2, B). Side effects include hypotension, diarrhea, hematoma, and increased pain due to neuritis.

Neuraxial Therapy

Neuraxial or intraspinal therapy involves the delivery of an analgesic into the epidural or subarachnoid space. In patients with germ cell tumors, this therapy should be considered for patients who have not responded to conservative treatment and who have more than one type of pain. This therapy allows opioid doses (and thus, their adverse effects) to be reduced, with the possibility of adding agents that will be more effective for neuropathic pain. The condition of the patient and the expected prognosis will guide the clinician toward the most appropriate modality. Once a system has been implanted and the therapy instituted, monitoring and titration of medication by trained personnel will still be necessary.51 The intrathecal delivery system involves the placement of a subarachnoid catheter, which is then tunneled subcutaneously and attached to a small pump, which, in turn, is placed into a subcutaneous pocket anteriorly (Figure 26-4). The capacity of the pumps is up to 50 mL for the nonprogrammable models and up to 20 mL for the programmable models (Figure 26-5). The pumps can be accessed per-cutaneously to refill the reservoir, and the infusion rates of the programmable models can be changed with an externally placed programmer. Doses via

Intravenous Injection Via Heparin Block
Figure 26-3. Celiac plexus block with computed tomographic guidance. Injection through needle via a left-sided approach shows dye spreading anteriorly away from the celiac plexus. Injection through needle via a right-sided approach shows dye anterior to the aorta, at the site of the celiac plexus.

this route are in the magnitude of 100 times less than the equivalent intravenous dose. Thus, if concentrated solutions and low infusion rates are used, patients will require less frequent visits. However, if changes in the infusion rate are required, the patient will need to visit for the pump to be reprogrammed.

The epidural space has a larger capacity than the intrathecal space and is a space from which the solution is able to diffuse. Therefore, an epidural infusion requires a significantly higher volume to achieve the same analgesia and will necessitate an external pump and drug reservoir. An epidural infusion with a temporary catheter can be used for short periods postoperatively, during painful diagnostic procedures, or while waiting for anticancer therapy to reduce pain. If the decision is made to continue this mode of therapy, a silicone catheter can be implanted (Figure 26-6) and tunneled to a larger percutaneous catheter anteriorly (Figure 26-7) or to a subcutaneous port. Both of these can be connected to an external portable pump and infusion bag or cassette. The proximal catheter tip should be placed as close as possible to the dermatomal distribution of pain and its position verified by the injection of radiopaque contrast dye (Figure 26-8). The combination of medications and the rate of infusion can be changed, and a bolus can be administered more eas-

Intrathecal PumpSubcutaneous Angiocatheter

Figure 26-4. Technique of intrathecal pump implantation. A, A catheter is threaded into the intrathecal space following verification of cerebrospinal fluid flow through the needle after the dura is punctured. B, The catheter is subcutaneously tunneled from the posterior incision to the site of the anteriorly placed subcutaneous pocket. C, The catheter is connected to a pump that is placed in the pocket.

Figure 26-4. Technique of intrathecal pump implantation. A, A catheter is threaded into the intrathecal space following verification of cerebrospinal fluid flow through the needle after the dura is punctured. B, The catheter is subcutaneously tunneled from the posterior incision to the site of the anteriorly placed subcutaneous pocket. C, The catheter is connected to a pump that is placed in the pocket.

Intrathecal Catheter
Figure 26-5. A programmable intrathecal pump with an 18 mL reservoir. (Courtesy of Medtronic Inc., Minneapolis, MN)

ily than with the intrathecal infusion. If skilled nursing is available, these changes can be made in the home, avoiding visits to the hospital.

Complications of both infusion therapies include pump failure, catheter leakage or disconnection, inadequate analgesia, urinary retention, and signs of local anesthetic block if a local anesthetic drug is used. A cost analysis of both systems showed that the initial cost was higher with the implanted pump but that the cost of the external system was higher after 3 months.52 The risk of infection is higher with the epidural infusion, owing to the externalized nature of the therapy.53 The decision regarding the appropriateness of either therapy is often made according to the prognosis of the patient.

Opioids act on spinal cord opiate receptors and produce analgesia when given via the intraspinal route.54 The most widely used drug for intraspinal therapy is morphine although hydromorphone, fen-tanyl, and sufentanil have also reportedly been used. Opioids are the drugs of choice when the pain is predominantly somatic, but when they are combined with a local anesthetic drug, a synergistic effect and improved analgesia for neuropathic pain occur. The combination will reduce side effects while avoiding the development of tachyphylaxis to the local anesthetic, which is seen when it is given alone.

Clonidine can also be administered via the intraspinal route. It is an a2-adrenergic agonist that results in an inhibition of the release of substance P and a decrease in the transmission of neuropathic pain at the spinal cord level. Its side effects include sedation, dry mouth, and decreased heart rate.55

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