**1. Pain**

Pain is one of the most common ailments which drive patients to a clinic, and pain alleviation is a key factor in the understanding of the well-being. There is a heightened awareness of pain as the "fifth vital sign," therefore it should be monitored as cautiously as blood pressure, temperature, respiratory rate, and pulse. This also entails a change in paradigm, which means pain treatment has shifted from decisions taken by an individual physician with an unspecified follow-up to more systematic approach by multidisciplinary teams [1, 2].

Pain is defined by WHO as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage." The inclusion of the word "emotional" is crucial for the understanding of the implications of pain perception by a subject. The obvious consequence of this is that that pain perception is unique to each individual, as well as pain threshold is different in subjects. Cultural aspects should also be considered as it is nowadays preconized that no one should experience pain, not even when giving birth. Pain is culturally determined and cannot be defined so coarsely when it has so many influencing factors on how it is apprehended and expressed, being culture one of the most efficacious ones [3–6]. The clinician should then make a great effort to conceptualize pain in the search for pain alleviation because pain relieving is one of the main goals in practice.

Even though it is an ailment common to many diseases and medical procedures and in many cases, an illness in itself, it is not common to find a specialization on pain in medical schools. In general, pain management or pain medicine should entail, though not always does, a multidisciplinary approach for easing the suffering and improving the quality of life of those patients suffering from it [2, 7–9].

Although it may not be correct, it is possible to distinguish between acute and chronic pain. The first one has gained more attention because the success in its treatment, due to advances in pharmacology, and also because it is generally easily associated with a biomedical pathological cause. It is also in this kind of pain that neurophysiological explanations are fundamental for its understanding [10].

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In acute pain, a pharmacological approach is usually successful in the treatment because in general a biological approximation to the matter is acceptable. Collectively, non-steroidal anti-inflammatory agents (NSAIDs) and acetaminophen (paracetamol) are the most commonly used pain medications, followed by opioids generally used in moderate to severe pain [11, 12].

The definition aforementioned is not adequate for chronic pain because chronic pain does not only entail a biological state but also a psychological one, which in many cases is able to control patients' lives. An ordinary approximation to chronic pain would give us a false impression that it can be successfully treated by the ample arsenal of drugs available; however, in many aspects, chronic pain is still an enigma for medicine. Chronic pain may be defined then as a state of sensitized perception of pain that exceeds the simple sensorial experience. Medicine treats injury and pathology to support and speed healing and treats distressing symptoms such as pain to relieve suffering during treatment and healing. When a painful injury or pathology is resistant to treatment, when pain persists after the injury or pathology has healed, and when medical science cannot identify the cause of pain, the task faced is much more difficult. The obvious consequence of this is that treatment approaches to chronic pain not only include pharmacologic measures, such as analgesics, tricyclic antidepressants, and anticonvulsants but also interventional procedures, physical therapy, and psychological measures [10, 13–16]. As a consequence of this, the typical chronic pain management team includes anesthesiologists, occupational therapists, physiotherapists, clinical psychologists, and pain nurses. Together the multidisciplinary team can help create a package of care suitable to the patient. While acute pain usually resolves once the underlying trauma or pathology has healed and is treated by one practitioner, effective management of chronic pain frequently requires the coordinated efforts of multiple disciplines [14].
