Sex Differences in the Morphine-Sparing Effects of Intraoperative Dexmedetomidine in Patient-Controlled Analgesia Following General Anesthesia

Previous studies have reported that intraoperative dexmedetomidine has morphine-sparing effects in patient-controlled analgesia (PCA). The present study was designed to investigate the possible sex differences in the morphine-sparing effects of intraoperative dexmedetomidine following general anesthesia. A total of 223 patients scheduled for surgeries under general anesthesia were divided into female and male groups. Each group was then subdivided into 2 subgroups that were maintained using propofol/remifentanil/dexmedetomidine (PRD) or propofol/remifentanil/saline (PRS). During the first 24 hours postsurgery, both female and male PRD patients had lower scores on a visual analog scale (VAS) (fPRS vs fPRD, P < 0.05 or P < 0.01; mPRS mPRD, P < 0.05, P < 0.01, or P < 0.001) and consumed less morphine than their controls from the PRS group (fPRS vs fPRD, P = 0.0392; mPRS vs mPRD, P = 0.0041). Interestingly, the female PRD patients had similar VAS scores (fPRD vs mPRD, P > 0.05) and consumed comparable morphine compared to the male PRD patients (fPRD vs mPRD, P = 0.4238). However, when normalized to body weight, they consumed much more morphine than male PRD patients (fPRD vs mPRD, P < 0.001), and this effect was not seen in the PRS patients. Intraoperative administration of dexmedetomidine appeared to have a stronger morphine-sparing effect in controlling postoperative acute pain in male patients than in female patients.