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Cancer pain is usually caused directly by neoplastic injury to
pain-sensitive structures. For this reason, primary antineoplastic
therapy, including radiation, chemotherapy, and palliative surgery, should
be considered part of an analgesic strategy in some cases. When
therapy directed at the tumor is inappropriate, is not feasible,
or is ineffective, symptomatic analgesic therapies become the overriding
concern. Opioid-based pharmacotherapy is the mainstay approach,
but adjunctive anesthetic, surgical, psychiatric, and physical modalities
may be essential in some cases (See Chapter 46, Anesthetic Interventions
in Cancer Pain). Pharmacologic approaches may be systemic or regional
(anesthetic). This chapter addresses only systemic pharmacologic
analgesics.
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The World Health Organization (WHO) proposed a three-step approach
to the selection of drugs for the treatment of cancer pain (Fig.
45-1).1 The first step, for mild pain, utilizes
non-opioid analgesics and adjuvant drugs. Adjuvant drugs can be
either nontraditional analgesics (so-called adjuvant analgesics)
or drugs added to manage the side effects of the primary analgesics.
For more intense pain, an opioid is added. Some opioids are used
conventionally for moderate pain and others are used for severe
pain. This approach is designed to be simple to understand and useable
around the world. Uncontrolled field testing has found the WHO guidelines
effective for 70% to 100% of patients with cancer.2
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Pain is often underrecognized in cancer patients. Cleeland et
al surveyed outpatients with metastatic cancer and physicians from
54 treatment centers.3 They found that 42% of
597 patients with pain were not receiving adequate analgesia by
the WHO guidelines (Fig. 45-1). Insufficient pain relief was particularly
common among minorities, women, and the aged. An important barrier
to effective pain management was a discrepancy between the patient’s
and physician’s assessments of the extent to which pain
was interfering with daily activities. The data underscore the importance
of accurate pain assessment in providing adequate cancer pain relief.
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The assessment should allow inferences about the pain mechanisms,
identification of the pain syndrome (See Chapter 44, Cancer Pain
Syndromes), and classification of the relationship between the pain
and the disease. The clinician must also assess the functional impact
of the pain and psychosocial comorbidities. It is essential to accept
the patient’s report of pain at face value. Pain should
be assessed frequently and systematically, especially when a new
pain is reported or a new analgesic treatment is initiated. The
location, intensity, and quality of the pain, aggravating and relieving
factors, and the patient’s emotional and cognitive response
to pain should be noted.
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Pain Measurement
Tools
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Although there is no quantitative biochemical or neurophysiologic
test for pain, tools have been devised to assess pain intensity 4 (See ...