Fig. 3. A model illustrating hypothetical conditions necessary to preempt or reverse pain hypersensitivity with neural blockade. (Top ) A nociceptive input caused by incisional injury, inflammatory injury, or both, with width of band indicating input intensity. (Bottom ) Five possible variants of pain hypersensitivity generated in response to the afferent input with different block conditions: No block (1), shorter (2) and longer-lasting (3) preinjury blocks, and shorter (4) and longer-lasting (5) blocks administered when pain hypersensitivity is already established. A = Time after which nociceptive input is unable to initiate pain hypersensitivity yet strong enough to reinitiate it (if it was already established before the block); B = time after which the input is unable to reinitiate pain hypersensitivity but can maintain it (until time C). Periods when initiation, reinitiation, or maintenance of pain hypersensitivity are possible are indicated by pink, yellow, and blue, respectively. The effectiveness of a potential preemptive effect is determined by duration of nociceptive input that can initiate and maintain central hypersensitivity. If the blockade lasts until afferent input subsides to the level at which it cannot trigger central hypersensitivity, the preemptive effect might be clinically meaningful (see points 2 and 3). The reversal of central hypersensitivity (see points 4 and 5) is determined by two factors: persistence of central sensitization and continuance of the afferent input that can initiate, reinitiate, and maintain (respectively, in accordance with the declining level of the input intensity) pain hypersensitivity. The blockade should last until central sensitization subsides and the intensity of the afferent input is below the level that could potentially reinitiate central hypersensitivity (point 5). Because the intensity of afferent input for reinitiation of central hypersensitivity is lower than that for its initiation, blockade for a successful reversal of pain hypersensitivity should be longer (to permit greater input fading) than that for preemptive effect. (Modified with permission from Kissin et al.  15)

Fig. 3. A model illustrating hypothetical conditions necessary to preempt or reverse pain hypersensitivity with neural blockade. (Top ) A nociceptive input caused by incisional injury, inflammatory injury, or both, with width of band indicating input intensity. (Bottom ) Five possible variants of pain hypersensitivity generated in response to the afferent input with different block conditions: No block (1), shorter (2) and longer-lasting (3) preinjury blocks, and shorter (4) and longer-lasting (5) blocks administered when pain hypersensitivity is already established. A = Time after which nociceptive input is unable to initiate pain hypersensitivity yet strong enough to reinitiate it (if it was already established before the block); B = time after which the input is unable to reinitiate pain hypersensitivity but can maintain it (until time C). Periods when initiation, reinitiation, or maintenance of pain hypersensitivity are possible are indicated by pink, yellow, and blue, respectively. The effectiveness of a potential preemptive effect is determined by duration of nociceptive input that can initiate and maintain central hypersensitivity. If the blockade lasts until afferent input subsides to the level at which it cannot trigger central hypersensitivity, the preemptive effect might be clinically meaningful (see points 2 and 3). The reversal of central hypersensitivity (see points 4 and 5) is determined by two factors: persistence of central sensitization and continuance of the afferent input that can initiate, reinitiate, and maintain (respectively, in accordance with the declining level of the input intensity) pain hypersensitivity. The blockade should last until central sensitization subsides and the intensity of the afferent input is below the level that could potentially reinitiate central hypersensitivity (point 5). Because the intensity of afferent input for reinitiation of central hypersensitivity is lower than that for its initiation, blockade for a successful reversal of pain hypersensitivity should be longer (to permit greater input fading) than that for preemptive effect. (Modified with permission from Kissin et al.  15)

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