Transcutaneous Electrical Acupoint Stimulation of P6 to Prevent Postoperation Nausea and Vomiting

150 female patients, aged between 18 to 60 y, who are scheduled for elective gynecological laparoscopic surgery requiring general anesthesia, will be randomly allocated by a computer generated randomization table to acustimulation group (Group Acu), tropisetron group (Group Trp),or dexamethasone group (Group Dxm).

In Group Acu, a surface electrode will be applied in the induction room to the P6 acupoint 30 min before induction.An operator will set electric stimulating current at 1mA with frequency at 2 Hz, and gradually increased the current intensity to a little below discomfort threshold.The stimulation will be maintained until the patient is discharged from the post-anesthesia care unit (PACU). In Group Trp and Group Dxm, the same protocol will be applied unless silicone covers attached to both electrodes.

A standardized anesthetic protocol will be followed. After induction, dexamethasone 10mg i.v. will be given in all groups. All patients will receive intravenous lactated Ringer's solution based on calculated preoperative deficits, surgical procedure, and estimated intraoperative blood loss. Parecoxib 40mg i.v. during surgery and incision infiltration of 0.5% ropivacaine at the end of surgery will be used for post-operative analgesia. After surgery, analgetic therapy will continue with morphine upon patient's request.After extubation, patients will be transported to PACU and observed for no less than 30 min. Metoclopramide 10mg i.v. will be administered as a rescue therapy to any patient who experiences an episode of moderate or severe nausea, an episode of vomiting, and requests rescue medication.

At the start of skin closure, a prefilled syringe which contains 5 ml of a solution will be administered intravenously to the patient. It will contain either saline (Group Acu and Group Dxm) or tropisetron 5mg (Group Trp).The syringe with the drug will be prepared by a study coordinator according to group allocation.

The patients, the anesthesiologists, and the nursing staff shall be unaware of the group assignments.

An anesthesiologist and an anesthetic nurse, who are trained for the study and blinded to the randomization, will collect the data.

Inclusion criteria

• American Society of Anesthesiologists (ASA) physical status I or II
• aged between 18 to 60yr
• scheduled for elective gynecological laparoscopic surgery requiring general anesthesia

Exclusion criteria

• pregnancy or breastfeeding
• mental retardation
• psychiatric or neurological disease
• use of antiemetics, emetogenic drugs, opioids or glucocorticosteroids within 3 days prior to surgery
• known allergy to tropisetron or dexamethasone
• nausea and/or vomiting within 24 hr prior to surgery
• implantation of a cardiac pacemaker, cardioverter, or defibrillator
• any skin problem at the acupoint stimulation area