Pain may be defined as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage" (International Association for the Study of Pain, Subcommittee on Taxonomy, 1979). Although the mechanisms of pain and pain pathways are becoming better understood, it should be emphasized that an individual's perception of pain and appreciation of its meaning are complex phenomena that involve psychological and emotional processes in addition to activation of nociceptive pathways (McGrath, 1990a). Pain intensity is not proportional to the type or extent of tissue damage but may be influenced at many sites within the nervous system. The perception of pain depends on the complex interactions between nociceptive and non-nociceptive impulses in ascending pathways, in relation to the activation of descending pain-inhibitory systems. This framework provides the basis for a comprehensive, multimodal approach to the assessment and treatment of patients with pain and fits with the clinical observation that there is no single approach to effective pain management. Instead, individualized pain management should take into account the stage of disease, concurrent medical conditions, characteristics of pain, and psychological and cultural characteristics of the patient. It also requires ongoing reassessment of the pain and treatment effectiveness.
Figure 1 is a flowchart depicting cancer pain management from the initial assessment of pain and its cause to the various treatment modalities, including the WHO analgesic ladder and numerous other drug and non-drug modalities (World Health Organization, 1990). The best choice of modality often changes as the patient's condition and the characteristics of the pain change. It is important that the effectiveness of analgesic modalities used separately or in combination be carefully assessed. The flowchart indicates the complexity of both the sources of pain and the types of modalities available for managing it. This guideline elaborates on the modalities, making recommendations about their appropriate use. Whenever pain is present, clinicians should provide optimal pain relief by routinely assessing pain and treating it with one or more of the modalities described here.
The WHO ladder (Figure 2) portrays a progression in the doses and types of analgesic drugs for effective pain management. When this noninvasive approach is ineffective, alternative modalities include other routes of drug administration, nerve blocks, and ablative neurosurgery (Figure 3). As Figure 3 indicates, patients receiving treatments of varying degrees of invasiveness may also benefit from other modalities; the number of patients receiving these modalities either separately or in combination has not been well documented. The estimates presented in Figure 3 reflect various clinical populations and may not represent all settings and populations; furthermore, they do not necessarily reflect what is optimal, but only a range of current opinions. There is a need for research to determine the effectiveness of many of these modalities used alone or in combination for different patient populations in various settings.
The WHO Ladder
PAIN IN SPECIAL POPULATIONS
Suicide and Cancer Pain
MONITORING THE QUALITY OF PAIN MANAGEMENT