Preventative effect of ketamine on post-surgical hyperalgesia induced at a body part remote from the surgical site.

BACKGROUND: It is known that pain hypersensitivity can be induced at a body part remote from a surgical site (tertiary hyperalgesia), leading to patient discomfort. Nevertheless, no reported study to date has investigated methods to attenuate such tertiary hyperalgesia. Ketamine is known to modulate hyperalgesia induced by central sensitization. Thus, we investigated whether intraoperative administration of ketamine could decrease post-surgical tertiary hyperalgesia in patients undergoing a laparoscopic hysterectomy.

METHODS: In total 46 patients were studied. Ketamine (1 mg/kg IV and 0.5 mg/kg/h or the same volume of 0.9% saline) was administered during surgery in the ketamine and control groups, respectively. The mechanical pain threshold was measured on the patients' dominant palm before and 24 hours after the surgery to evaluate hyperalgesia.

RESULTS: The change in mechanical pain threshold over time (preoperative and postoperative) differed between the groups, with a lower postoperative threshold in the control group (118.6±170.5 vs. 419.2±233; P=0.015). The postoperative visual analogue scale score at rest was lower in the ketamine group (22±16 vs. 13±9; P=0.02). Visual analogue scale scores during deep breathing, consumption of analgesia and antiemetics, and the incidence of dizziness did not differ significantly between the groups (P>0.05).

CONCLUSIONS: These results suggest that the intraoperative administration of ketamine may decrease post-surgical hyperalgesia developing at a region remote from the surgical site.