Mechanisms of postoperative pain: clinical indications for a contribution of central neuronal sensitization.
BACKGROUND
The relative importance of different nociceptive mechanisms for the intensity, duration, and character of postoperative pain is not well established. It has been suggested that sensitization of dorsal horn neurones may contribute to pain in the postoperative period. We hypothesized that wound hyperalgesia in postoperative patients and experimentally heat-induced secondary hyperalgesia share a common mechanism, sensitization of central neurones, and consequently, that the short-acting opioid remifentanil would have comparable effects on hyperalgesia in both conditions.


METHODS
In a randomized, controlled, double-blind trial, we assessed mechanical hyperalgesia in skin bordering the surgical wound, and an area of experimentally heat-induced secondary hyperalgesia on the thigh, in 12 patients who underwent abdominal hysterectomy within 5 days prior to the investigation. Observations were made before and during a drug challenge with remifentanil, which has been demonstrated to reduce the area of heat-induced secondary hyperalgesia in volunteers.


RESULTS
The area of skin with surgically-induced mechanical hyperalgesia, the area of heat-induced secondary hyperalgesia, and pain during cough, were significantly reduced during remifentanil infusion compared with placebo (P = 0.008, P = 0.006, and P = 0.002, respectively). The relative reduction (% of baseline) of the area of skin with surgically-induced hyperalgesia and heat-induced secondary hyperalgesia during infusion of remifentanil was significantly associated (R2 = 0.72, P = 0.001).


CONCLUSIONS
Although remifentanil is not a highly targeted "antihyperalgesic," these results support the hypothesis that both wound hyperalgesia in postoperative patients and experimentally heat-induced secondary hyperalgesia may share common mechanisms, and that central neuronal sensitization may contribute to some aspects of postoperative pain. Antihyperalgesic drugs should be further developed and evaluated in clinical trials of postoperative pain.
Dirks
Jesper
J
Laboratory of Pain Physiology, Department of Anesthesiology and Intensive Care Medicine, Herlev University Hospital, Herlev, Denmark.
Møiniche
Steen
S
Hilsted
Karen-Lisa
KL
Dahl
Jørgen B
JB
D000328:Adult; D000368:Aged; D000701:Analgesics, Opioid / Q000627:therapeutic use*; D000768:Anesthesia, General; D004311:Double-Blind Method; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D006930:Hyperalgesia / Q000188:drug therapy* / Q000209:etiology; D007044:Hysterectomy; D008875:Middle Aged; D010147:Pain Measurement; D010149:Postoperative Pain / Q000188:drug therapy* / Q000209:etiology; D010880:Piperidines / Q000627:therapeutic use*; D000077208:Remifentanil
D000701:Analgesics, Opioid; D010880:Piperidines; D000077208:Remifentanil