General Treatment Principles
Pain is one of the most common reasons for which patients seek medical attention, yet it remains significantly undertreated despite the availability of effective medications and other therapies.32,33
Table 8-1 lists eight common causes of treatment failure when using analgesics.34 In general, the reasons include a lack of understanding of pain management principles or the pharmacologic properties of the drugs; an overestimation of the risk of addiction by both patients and caregivers; or poor communication between the patient and medical personnel. A number of steps to overcome these barriers are described in the succeeding section.
Effective analgesic therapy begins with an accurate assessment of the patient. The Pain Intensity and Pain Distress Scales (Figures 8-2 and 8-3, respectively) can help clinicians assess pain. When obtaining a pain history, it is important to gather details about the pattern, duration, location, and character of the pain. Pain intensity should be measured using an appropriate pain scale (Figs. 8-2 and 8-3) according to the patient's ability to communicate.17,24 Factors that exacerbate or relieve pain should be assessed. The names and amounts of all analgesics that the patient is taking should be documented as well as their effectiveness. In addition, other medical problems and medications should be documented, including over-the-counter and nonprescription remedies. A patient fearful of being accused of analgesic abuse might be reluctant to give an accurate drug use history unless a trusting relationship can be established.
| Figure 8-2 Pain intensity scales. (Adapted from Patt RB. Cancer Pain. Philadelphia: JB Lippincott; 1993; and Wong DL. Whaley and Wong's Essentials of Pediatric Nursing. St. Louis: Mosby; 1997, with permission.) |
| Figure 8-3 Pain distress scales. |
Effective treatment considers the cause, duration, and intensity of pain and matches the appropriate intervention to the situation. The goal of therapy is to eliminate or reduce the pain to the lowest tolerable intensity and prevent it from recurring, rather than waiting to treat the pain when it becomes unbearable. The patient should predetermine this lowest tolerable level with the health care provider based on a pain scale that is mutually understood. Guidelines from the World Health Organization, summarized in Table 8-2, can be useful when choosing initial therapy.35 It is also important to consider the clinical situation when determining analgesic selection or whether the painful condition requires analgesic therapy. For example, it would be irrational to use morphine to treat the severe abdominal cramping pain associated with constipation, because morphine can worsen the constipation. If pain is the result of a fracture, then stabilization and immobilization, in addition to appropriate analgesics, will reduce pain in the affected bone. Once a pain regimen is initiated, frequent reassessment will determine whether the goals of therapy are being met and whether they address any emerging side effects. Drug selection, doses, routes of administration, and dosing frequency should be adjusted as needed until the goals of therapy are met. In treating acute, severe postoperative pain, it may be necessary to begin with a potent opiate analgesic and then gradually reduce the dose based on the patient's clinical response.
| Table 8-2 Example Initial Regimens for Different Pain Levels Based on Guidelines From the World Health Organization (WHO) | |||||||||||||||||||||||||
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When treating chronic pain, elimination and prevention of pain is best accomplished by using analgesics at fixed time intervals (“time-contingent”) rather than on an as-needed basis. The traditional as-needed analgesic dosing schedule is inadequate much of the time, leading to greater 24-hour drug intake and a pattern of stepwise increases in dosage. Therefore, most pain management specialists now administer, or at least offer, analgesics to their patients on a schedule, at least for the first few days until pain requirements can be adequately assessed. In patients with severe acute or malignant pain, however, scheduled analgesics alone may not be adequate without additional analgesics for breakthrough episodes. Until the dosage is stabilized, all patients who are receiving analgesics should be monitored closely for efficacy of analgesia as well as untoward side effects. Successful pain management can also include the use of nonpharmacologic measures, such as ensuring that the patient receives adequate rest and emotional support. Physical and occupational therapy may be useful to help improve strength or mobility and to ensure that no barriers at home or work exist that can interfere with the patient's activities of daily living.28
Anxiety and guilt often complicate the management of pain. Patients sometimes become anxious, fearing that their pain will become uncontrollable or that they will become addicted to opiates. Also, patients sometimes feel guilty about taking opioids for their pain because of the negative social connotations associated with these drugs. They may feel that they have failed their clinicians' expectations. Therefore, patient education about the rational use of analgesics is imperative. Pain can be managed best when trust and communication exist between the caregiver and the patient, known as a therapeutic alliance. Patients must feel comfortable telling caregivers whenever their pain needs arise, and caregivers must respond appropriately and in a timely fashion. Good communication between caregivers and patients can alleviate anxiety and guilt regarding patients' pain needs.
Patient-specific characteristics (e.g., age, gender, race, organ dysfunction, and comorbidities) play an important role in the response to pharmacotherapy, ranging from subtherapeutic effect to toxicities. A genetic polymorphism of the cytochrome P450 system significantly contributes to inconsistency of patient response to drug therapy.36 Based on CYP 450 enzymatic activity, patients may be classified as poor metabolizers, intermediate metabolizers, extensive metabolizers, and ultrarapid metabolizers. Such variations in drug metabolism have been correlated to a range of effective doses and occurrence of toxicities. This has been observed with different drug classes, including opioids.36
Codeine is a prodrug that is metabolized to morphine, a more potent analgesic, by CYP2D6. This particular enzyme is known to have variable presence among individuals, leading to insufficient analgesia in poor metabolizers.37
Tramadol, a synthetic opioid, exerts its full analgesic effect when the parent compound is converted to O-desmethyltramadol via CYP2D6. Consequently, it has been demonstrated that, in the postoperative setting, poor metabolizers do not exhibit equal analgesia when compared with extensive metabolizers.37
Polymorphism of CYP 450 is not the only target of pharmacogenomic research. Genetic variations that contribute to opioid, cannabinoid, NMDA, dopamine, and serotonin receptor expression, as well as drug transporters, are also subjects of further research. Their effect on response to pharmacotherapy has not yet been elucidated.37
In the near future, when genetic testing becomes economically feasible for widespread use, clinicians will utilize this information in their decision process to prevent toxicities and optimize pharmacotherapy.37
Analgesic Selection
The selection of an analgesic must be individualized for each patient, depending on the cause and chronicity of the pain as well as the patient's age and concomitant medical conditions that may alter drug response. Furthermore, the clinical response of the patient dictates future dose adjustment, route, and desired dosing interval. The selection of an opioid for the management of severe acute and chronic malignant pain must always include consideration of morphine or one of the other potent opioids; however, the role of NSAID should not be overlooked. Adjunctive analgesic medications, such as antidepressants or anticonvulsants, are often added because chronic nonmalignant pain can be associated with sympathetic dysfunction and neuropathies. An NSAID is the analgesic of choice in the management of mild to moderate pain involving musculoskeletal tissues and also are extremely effective in the management of pain from bony neoplastic metastasis. Neurogenic pain often responds better to tricyclic antidepressants (TCA) than to opioids. Neuropathic pain may not be relieved by opioids until the dose is high enough to also cause significant side effects.
If the maintenance dose of an opioid analgesic is too high, the patient can become oversedated and less functional. In extreme cases, patients may become bedridden from excessive opiate use. When given the choice of eliminating the last trace of discomfort at the cost of some sensorial clouding, patients invariably select full alertness and the continued presence of some pain.38,39 Patients who are receiving opioids also need to be monitored for deterioration in vital signs (pulse and respiratory rate), constipation, and urinary retention. Stool softeners and other prophylactic measures, such as stimulant laxatives, may be required. Similarly, a patient who is receiving NSAID or adjunctive analgesics should be monitored for possible untoward side effects associated with such medications.
Orally or transdermally administered analgesics allow a patient a greater degree of independence and control over daily activities than parenteral administration by maximizing mobility. Similar advantages can be obtained with an intravenous (IV) infusion device, particularly a portable programmable infusion pump. Regular parenteral administration by other routes can be difficult and painful in cachectic patients.
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