|
|
Nerve Blocks
The possibility of controlling otherwise intractable pain by the relatively brief application of a local anesthetic or neurolytic agent makes neural blockade an attractive approach in selected patients. Published estimates of the percentage of all patients with pain for whom nerve block procedures may appropriately be considered vary greatly. Allowing for vagueness in methods of arriving at published estimates, lack of uniformity in clinical conditions treated by neural blockade, and in reported clinical outcomes, it still appears that some 50 to 80 percent of patients who receive nerve blocks for pain may benefit.101 (See Table 19)
Nondestructive or destructive agents can be used for nerve blocks. In the former, a local anesthetic such as lidocaine or bupivacaine is typically applied at an anatomically defined site to provide diagnostic information (e.g., whether the pain is somatic or visceral; whether it has a sympathetic mechanism) and to assess side effects such as hypotension and subjective sensations, including pain relief or unpleasant numbness, likely to result from a planned neurodestructive procedure. Although the lack of a desirable result from local anesthetic injection after proper needle placement generally predicts the failure of a neurolytic block, a promising result after local anesthetic injection does not guarantee the success of subsequent chemical destruction.
Injections of a local anesthetic may provide relief that outlasts its pharmacologic action. Pneumothorax, hemorrhage, or infection are rare complications of nerve blocks but nonetheless mandate resuscitative skills and short-term followup. The injection of an anti-inflammatory corticoid with a local anesthetic into the spinal space or around nerve roots can reduce edema and irritation produced by tumor compression and provide analgesia for up to weeks. One or more cervical or lumbar sympathetic blocks may result in prolonged relief in patients whose cancer-related pain is sympathetically maintained. When single sympathetic blocks produce only transient benefit, the placement of a catheter at the sympathetic ganglion (or the corresponding intraspinal segments or interpleural space) to enable continuous sympathetic blockade for days to weeks may produce sustained benefit.
Patient selection and timing of neural destruction for pain relief are based on the exhaustion of more conservative modalities, a lack of available, clinically superior options, and the availability of capable physician and support systems after the procedure. Nondestructive analgesic infusion techniques can preempt the need for neurolytic procedures. Therapeutic choices depend on patient and family preferences and the clinical judgment of their health care providers.483
Peripheral nerve destruction can be accomplished by the injection of ethanol, phenol, or other neurolytic agents at sites ions test injection of local anesthetic has produced pain relief. Whereas phenol induces warmth and then numbness, alcohol produces intense transient burning after injection and hence should be immediately preceded by local anesthetic injection. Small volumes of alcohol or phenol may be injected intrathecally to destroy nerve root function in a localized distribution. Approximately 60 percent of patients treated with intraspinal alcohol or phenol experience complete or near-complete relief of pain until death.395 When a patient is painfree after neurolysis, opioids should not be stopped abruptly, lest a withdrawal syndrome be provoked. Complications including paresis, paralysis, and bowel or bladder dysfunction affect 0.5 to 2 percent of patients treated with intraspinal alcohol or phenol.175 An epidural injection of phenol (or alcohol, according to some reports) can accomplish the same goal; however, the targeting of the injectate is less precise, the neurolytic effects take place over a more diffuse area than that affected by the intrathecal route, and the technique is less well established than intrathecal injection.405
Neurolytic sympathetic blockade is useful to relieve pain in the arm, head and neck (stellate ganglion), or leg (lumbar sympathetic block), as well as to interrupt the visceral referent pain pathways mediating pain in the pancreas and other upper abdominal organs (cellar block) or in the pelvis (hypogastric block). Side effects of celiac block include transient hypotension and diarrhea; complications (less likely with radiologic guidance) include paraplegia or less severe radicular weakness or numbness, intrarenal injection and damage, retroperitoneal hematoma, and failure of ejaculation.227; 474 Four-fifths or more of patients with pancreatic or other abdominal cancers derive pain relief from celiac block, usually lasting until death.68; 128 Even when relief is incomplete, patients may appreciate the ability to lower their opioid dosage and by doing so reduce drowsiness and constipation. It thus appears reasonable to consider early celiac neurolytic block for patients with a short life expectancy and pain from pancreatic cancer.325 A recently reported technique for refractory chest wall tumor pain is interpleural blockade, which uses long-term local anesthetic infusion or single-dose phenol.
Neurolytic blockade of peripheral nerves should be reserved for instances in which other therapies (palliative irradiation, TENS, pharmacotherapy) are ineffective, poorly tolerated, or clinically inappropriate. Suitable targets for this approach include intercostal nerves at the site of painful tumor, after maximal doses of radiation and systemic analgesics, or nerves of the head and neck (e.g., gasserian ganglion). Pain recurrence due to neuritis is common because an alcohol-damaged nerve regenerates over weeks to months. If the mechanism of pain is partial or complete denervation, this will not be corrected (and may potentially be worsened) by further chemical damage to the nerve.
Pain that is diffuse (e.g., from multiple bony metastasis) may respond to chemical ablation of the pituitary, which is accomplished by alcohol administered through a needle advanced transnasally until its tip rests in the pituitary fossa. Pain relief by this intervention may be rapid and striking, while ascending nociceptive pathways remain unharmed. Pain relief has been reported in about two-thirds of patients, whether or not the primary tumor is hormone dependent.456 Complications include headache, persistent leakage of CSF, coma, and cranial nerve palsies, all of which occur at a frequency of 5 percent or less.98 Diabetes insipidus is a predictable side effect of complete pituitary ablation. Technical aspects of the above procedures are beyond the scope of this guideline and are well described in a number of recent monographs.3; 101; 450 Because of the appeal of nerve blocks for use in intractable pain and their potential for harm as well as benefit, clinicians should:
Screen patients according to coexistent medical conditions (e.g., coagulopathy); ability to understand risks of the proposed procedure (e.g., paresis or incontinence); and ability to cooperate during the procedure (e.g., not move). Consider a block only if the person planning to do it is experienced and skillful; prepared to deal with its immediate effects and side effects (e.g., hypotension, respiratory depression, or paralysis); and able to provide followup assessment and treatment. Use radiographic control for blocks when ease and safety depend on the precise identification of landmarks.
Go to the Non Pharmacologic Treatment of Pain in HIV Menu
Go to the Pain & HIV/AIDS Menu
Go to the HIVpositive.us Main Menu
74