Prevention of Postoperative Nausea and Vomiting (PONV) in Surgical Patients

Anesthesia has become remarkably safe during the past two decades, yet postoperative nausea and vomiting (PONV) continues to be a vexing problem with an unacceptably high incidence. Multiple factors including age, gender, type of surgery and anesthetic agents, perioperative opioid use and duration of anesthesia have been implicated in the cause of PONV. Several new drugs have been introduced during the last two decades to minimize PONV; however the incidence still remains significantly high, ranging from 30% during the first 24 postoperatively to 35% post discharge. Unrelenting PONV results in delayed discharge which is particularly significant after outpatient surgery. The proposed study will examine the anti-emetic properties of orally administered dronabinol given immediately prior to surgery with standard of care intravenous ondansetron given at the end of a surgical procedure in an effort to assess the need for cost effective prophylaxis of PONV.

The chemoreceptor trigger zone (CTZ) functions as emetic chemoreceptor for the vomiting centers. Many antiemetic drugs acting at the level of the CTZ are responsible for vomiting in patients receiving chemotherapy and postoperative patients. Our regimen of oral dronabinol has been proven to reduce the incidence of PONV in patients receiving chemotherapy. We intend to prove that a regimen that has been utilized in patients receiving chemotherapeutic drugs will work in patients with a high risk for developing PONV following surgery. We hypothesize that a regimen of preoperative low dose of dronabinol is superior in efficacy to a standard antiemetic in preventing the incidence of PONV, and thus will not only improve patient satisfaction but will also reduce length of stay in patients undergoing outpatient surgery.

Specific Objectives

• Reduction of postoperative and postdischarge nausea and vomiting in ambulatory surgery patients.
• Reduce rate of hospital admissions and length of inpatient stay after outpatient surgery.
• Improve patient satisfaction after outpatient surgery.

Procedure After informed consent, surgical patients scheduled for outpatient abdominal surgery at the Central Arkansas Veterans Healthcare System (CAVHS) who are at high risk for developing PONV following their procedure will be randomized to receive either the study drug ( preoperative oral dronabinol-5 mg) or standard therapy ( 4 mg ondansetron intravenously at the end of surgery). The outcome measures will be the presence or absence of PONV, the severity and number of such episodes, the event count of rescue antiemetic use and patient satisfaction. All data will be recorded by personnel who are blinded to the drug regimen.

Relevance:

At CAVHS, 2/3 of our patients are scheduled for outpatient surgical procedure everyday. Our regimen will minimize postoperative and postdischarge nausea and vomiting, improve post-operative care unit (PACU) length of stay, minimize unnecessary hospital admissions, provide patient satisfaction and cost containment. The potential for application of this inexpensive intervention to other surgeries is enormous. Reducing the incidence of PONV could have a significant impact on patient satisfaction. The intervention is very low-risk, efficacious, and could substantially impact on the experience and the outcome of the Veteran undergoing surgery.

Inclusion criteria

• The patients undergoing outpatient operations for intra-abdominal or abdominal wall procedures (e.g. hernias) under general anesthesia.
• Patients that are at increased risk for PONV based on the Koivuranta risk scoring system, with inclusion of patients having a Koivuranta risk score (K score) of 2 or more.
• Ability to give informed consent.
• Veteran eligible for treatment.

Exclusion criteria

• Patients <18 years old
• Patients with a history of hypersensitivity to cannabinoids or sesame oil --Patients with current substance abuse.

Substance abuse will be identified meeting one or both of the following criteria:

• a) Review the participant's medical chart to identify inpatient, residential, or outpatient treatment for alcohol or drug dependence as recorded in the Veterans Health Administration Computerized Patient Record system (CPRS) within the preceding six months.

OR

• b) Patient report. Exclude patients who report current marijuana or cocaine use within the past 30 days.

If a drug screen is clinically indicated and is positive the patient will NOT be entered into the study.

• Patients taking medications known to have significant drug-drug interactions with the prescribed drug and study drugs, Dronabinol and Ondansetron, will be reviewed in Micromedex. Micromedex is a medication database used by Central Arkansas Veterans Healthcare System (CAVHS). If the drug could have a drug-drug interaction with either dronabinol or ondansetron the patients will NOT be entered into the study. If a drug is confirmed via Micromedex not to have a drug-drug interaction, the patient will be eligible for study participation.
• Pregnant women
• Patients with prolonged QTC intervals on electrocardiogram (EKG).
• Patients enrolled in another clinical trial at the time of randomization.
• Inability to adhere to study protocol