**5. Key definitions**

Acute pain is considered as a particular state where the patient experiences a biopsychosocial reaction to tissue lesion related to inflammatory states, and it can experience discomfort and the management can be very complex. Generally acute pain is limited to a time interval but, in some cases, it may perpetuate and transform in chronic pain. One of the purposes of acute pain is human preservation, and it limits conducts that place the patient in danger and promotes tissue healing [5].

Chronic pain is characterized as pain that endures beyond tissue healing and the related metabolic and inflammatory disruption in the body. This kind of pain affects completely the biopsychosocial sphere and promotes patient disability and hospital costs in an important manner [6].

Persistent postsurgical pain is documented in 10–50% of patients that undergo surgery; depending on the magnitude of the surgery some of these patients will experience acute severe pain, if this initial situation perpetuates patients can develop chronic pain. It is well documented that one of the main factors for persistent postsurgical pain is poor control of acute pain in the first hours of the postsurgical event. The IASP's classification system for chronic pain syndromes makes a particular description as "a persistent pain state that endures two or more months of the surgical event that cannot be explained by other causes." This is accompanied by different changes that affect the somatosensorial system that lead to central and peripheral sensibilization that finally will manifest as chronic pain and worsen the patient's quality of life [6].
