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In the past few years progress has been made in understanding the mechanisms and pathways involved in the modulation of pain, as well as in developing new therapeutic tools to provide satisfactory pain relief after surgery. The relationship between the intensity of acute postoperative pain and the duration of the patient's recovery and functional outcome has been well established. For these reasons, the prevention and treatment of acute pain had become the focus of great interest for perioperative specialists. Postoperative pain differs from chronic pain by its shorter duration and its requirement for immediate relief, which dictate the development of suitable management protocols. Preemptive and preventive analgesia also represent concepts that only apply to acute postoperative pain. Finally, it is important to recognize the role of acute pain in the development of chronic pain syndrome.

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Irrespective of its nature, pain is not an objective but rather a subjective symptom. In the surgical as well as medical environment, intrinsic and extrinsic factors affect individual pain thresholds. Accordingly, the clinician must be always aware that pain treatment must be approached using a multimodal and multipharmacologic approach; no one single technique by itself, including the use of continuous peripheral nerve block, provides adequate pain relief in all patients and in all circumstances. The first description of continuous peripheral nerve block was reported in 1946 by Paul Ansbro,1 who described the placement at the supraclavicular level of a blunt needle secured to the patient's skin using a cork, through which the needle was inserted before block placement. This cumbersome apparatus allowed the incremental injection of local anesthetic in order to prolong the duration of anesthesia in patients undergoing upper extremity surgery. In their report the authors used a short-onset/intermediate-duration local anesthetic, like 1% procaine. After an initial 40-mL bolus the authors injected incremental doses based on the duration of surgery, up to a final volume ranging between 120 mL for 1.5-h surgery and 220 mL for 4-h surgery. During the following 3 decades continuous perineural infusion techniques continued to be developed, and their indications extended; initially they were mainly used for upper extremity blocks, afterward they were also employed for lower limb blocks.

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In 1977 Selander2 reported on the injection of 30 to 50 mL of mepivacaine to conduct a continuous axillary block in 137 patients undergoing hand surgery, and in 1979 Manriquez and Pallares3 reported on the repeated injection of 20 mL of 0.25% bupivacaine every 6 h to prolong the sympathetic block and pain control for 4 days.

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In 1982 Matsuda and colleagues4 reported on the use of either 30 mL of 1% lidocaine with epinephrine followed by 15 mL intermittently (1.5–2.75 h) or 40 mL of a 0.5% bupivacaine and 1% lidocaine mixture followed by intermittent injection of 20 mL (1.25–4.3 h) in 50 patients undergoing upper extremity reimplantation. Subsequently most of the groups have focused their clinical protocols on the use of low concentrations ...

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