Preemptive analgesia refers to measures that prevent sensitization of cells within the spinal cord dorsal horn and other key sites within pain pathway. By definition, preemptive means" preventive" not simply " before " ( Daniel, 1996 ). The relief of pain following surgery is essential during the postoperative period. Several techniques have been advocated for postoperative pain relief . Injury causes inflammation, which can lead to prolonged sensitization of nociceptive pathways. Primary and secondary hyperalgesia are well-established aspects of this process . Hyperalgesia describes the phenomenon of increased pain intensity in response to a normally painful stimulus (Lindblom et al, 1986). Primary hyperalgesia refers to the changes in sensation within the injury , whereas secondary hyperalgesia refers to sensory changes in the undamaged tissue surrounding the injury ( Kilo et al, 1994 ). Secondary hyperalgesia reflects °enteral sensitization, whereas primary hyperalgesia results from either centeral or peripheral sensitization or a combination of the two , depending on the type of injury ( Koltzenburg et al, 1994 ). The clinical consequences of these functional changes are not clear, but it is known that these changes may reduce pain threshold, increase pain to suprathreshold stimuli, and may even lead to chronic pain. Thus, prevention of this sensitization appears to be a rational step in pain treatment. Several experimental studies have demonstrated advantages of preemptive analgesia ( Schmidt et al, 1995). However, clinical evidence is less convincing (Kehlet and Dahl, 1995 ). The explanation may be that duration of the nociceptive input in most clinical studies outlasts the |
