Surgical Pain Is Followed Not Only by Spinal Sensitization but Also by Supraspinal Antinociception

Abstract

SummaryNociception can produce segmental spinal sensitization or descending supraspinal antinociception. We assessed both types of sensory change after surgery during isoflurane-nitrous oxide anaesthesia with or without fentanyl before nociception. Patients undergoing back surgery received fentanyl 3 g kg 91(n : 15) or placebo (n : 15) before anaesthesia in a prospective, randomized, blinded study. Sensation, pain detection and tolerance thresholds to electrical stimulation were measured before operation at the arm, incision and herniated disc dermatomes (HDD) and 1, 2, 4, 6, 24 h and 5 days after operation, together with pain scores and patient-controlled morphine consumption (duration 24 h). For segmental effects, thresholds were normalized to the thresholds at a distant dermatome (arm). Raw pain thresholds were increased after operation (fentanyl 9 placebo) and were maximal at 4 h (pain tolerance in HDD: fentanyl ;5.2 mA (;62.7 %), placebo, ;3.8 mA (;44.2 %); P : 0.05 vs baseline for both).Normalized sensation thresholds decreased for placebo only (HDD/4 h : placebo, 91.8 (944.8 %), P : 0.05; fentanyl, ;0.1 (;5.5 %) ns). All changes returned to baseline by 24 h except for the placebo group normalized HDD sensation (d5: placebo, 92.4 (959.7) %, P : 0.05; fentanyl 90.1 (95.5 %) ns). Pain scores and morphine consumption were similar. The study demonstrated both supraspinal analgesia and spinal sensitization after surgery. Fentanyl administration before operation augmented the former while decreasing the latter, and hence sensitization, especially if neuropathic, may particularly benefit from pre-emptive analgesia. (Br.

Human Experimental Pain Models for Assessing the Therapeutic Efficacy of Analgesic Drugs

“…This was supported by the study in patients with osteoarthritis in which sensation and pain thresholds over the osteoarthritic joint and at a distant location were increased after treatment with tramadol (Wilder-Smith et al, 2001). However, with strong opioids, it is possible to demonstrate effect on postoperative pain, because both fentanyl and morphine were effective in patients undergoing elective disc surgery or abdominal hysterectomies (Wilder-Smith et al, 1996, 1998.…”

“…Few studies found an effect of opioids on electrical skin stimulation; an effect of tramadol was demonstrated on the pain detection threshold for electrical stimulations in one study in patients with osteoarthritis (Wilder-Smith et al, 2001). An effect of fentanyl was found on electrical stimulation of the skin in patients undergoing back surgery or abdominal hysterectomy (Wilder-Smith et al, 1996;Wilder-Smith et al, 1998).…”

“…Sensation, pain detection, and tolerance thresholds in response to electrical stimulation were measured before operation and 1, 2, 4, 6, 24 h, and 5 days after operation and were increased after fentanyl administration (Wilder-Smith et al, 1996). In another study by Wilder-Smith et al (1998), the effect of fentanyl was investigated in patients undergoing elective abdominal hysterectomy.…”

Changes in sensory processing after surgical nociception

“…Taken together, these results point toward generalized central sensory inhibition distant to surgery and central (spinal) sensory excitation in the innervation areas involved by surgical intervention. These first conclusions were strengthened and expanded in a study of patients undergoing surgery for herniated intervertebral discs, of which half had nonanalgesic general anesthesia (isoflurane and placebo) and half had the same general anesthesia supplemented by fentanyl [40]. All patients received patient-controlled morphine analgesia for the first 24 postoperative hours.…”

“…Psychophysical measures such as cutaneous sensation or pain thresholds are relatively easy to apply to the clinical context, not too time-consuming, and well validated, on the condition that subject and tester are adequately trained [40]. Ideally, such thresholds should be measured at multiple sites to obtain a comprehensive picture of sensory change.…”