We designed this study to determine the minimum dose of dexamethasone for preventing nausea and vomiting associated with the use of morphine by patient-controlled analgesia (PCA). Two hundred forty female patients were randomly assigned to receive dexamethasone 2, 4, 8, or 12 mg IV immediately before induction of anesthesia. Droperidol (0.1 mg/mL with morphine 1 mg/mL in PCA pump) and saline were used as controls. The complete response (no postoperative nausea and vomiting and no need for rescue antiemetic for a 24-h postoperative period) rates for dexamethasone 8 mg (72.2%) and 12 mg (78.9%) were significantly more than for saline (42.9%) (P < 0.05). Patients who received dexamethasone 12 or 8 mg also reported higher patient satisfaction than those who received saline (P < 0.05). These results were as effective as adding droperidol 0.1 mg/mL to the morphine PCA without causing drowsiness, restlessness, or arrhythmias. Smaller doses of dexamethasone (4 or 2 mg) were not effective for this propose. The results suggest that dexamethasone 8 mg IV is the minimum effective dose for the reduction of PCA morphine-related nausea and vomiting.
Implications: Morphine administration by patient-controlled analgesia (PCA) is often associated nausea and vomiting. In this double-blind study, the minimum effective dose of dexamethasone for reducing this complication was 8 mg. This was as effective as adding droperidol 0.1 mg/mL to the morphine PCA without causing drowsiness, restlessness or arrhythmias.