The addition of dexmedetomidine to i.v. PCA morphine resulted in superior analgesia, significant morphine sparing, less morphine-induced nausea, and was devoid of additional sedation and untoward haemodynamic changes.

The interaction between morphine and nalbuphine in PCA admixture on analgesia is additive. Combinations of morphine and nalbuphine in PCA can decrease the incidence of pruritus, and the antipruritus effect is ratio-dependent. This may provide a novel combination strategy of opioid agonist and agonist-antagonist for postoperative pain management after gynaecologic surgery.

An initial bolus of diphenhydramine 30 mg at anaesthetic induction followed by postoperative PCA with a 4.8:1, but not 1.2:1, diphenhydramine-morphine mixture provides an effective antiemetic efficacy without morphine-sparing effects.

The antiemetic efficacy of ultralow-dose naloxone combined with PCA morphine is limited by a cut-off ratio of naloxone to morphine of 1:10,000.

Combination of low-dose nalbuphine and morphine in PCA decreases the incidence of opioid-related nausea, without affecting the analgesia and PCA requirement. This novel combination can improve the quality of PCA used for postoperative pain control after gynecological surgery.