Plain English Summary
Background and study aims
A caesarean is an operation used to deliver a baby, which can be planned or used as an emergency procedure, when a natural birth is not an option. It involves making a cut in the mother’s tummy (abdomen) wall and the womb, through which the baby is taken through. A caesarean can be a planned (elective) procedure, if the need for it becomes apparent during pregnancy or if the mother asks for it. The procedure is usually performed when the woman is awake under regional anaesthtic (numbing of the lower half of the body). This often involves an injection of an anaesthetic (numbing agent) and pain killer (such as morphine) mixture into the spine in the lower back. The use of intrathecal (injection into the spine) morphine is an effective method for pain relief in postoperative cesarean section, but has undesirable side effects such as nausea, vomiting and itching. The aim of this study is to test two drugs to find out if they can reduce nausea, vomiting and itching after receiving intrathecal morphine: dexamethasone (which prevents inflammation (swelling)) and ondansetron (which blocks the chemicals in the body which can trigger nausea and vomiting).
Who can participate?
Pregnant women aged between 18 and 40 who are scheduled for an elective caesarean section with spinal pain relief.
What does the study involve?
Participants are randomly allocated to one of three groups, who each receive a different treatment through a drip when they have their pain killer injection into the spine before surgery. Those in the first group receive 4mg of ondansetron in 5ml normal saline (salt water). Those in the second group receive 4mg of dexamethasone in 5ml normal saline. Those in the third group receive 5ml normal saline only with no drugs added. During surgery and then two, six and 24 hours afterwards, participants in all groups are asked to rate their nausea and any vomiting is recorded. The risk of nausea and vomiting is then calculated for each group. Participants are also asked whether their skin feels itchy so that the risk of itchy skin can be calculated.
What are the possible benefits and risks of participating?
Participants benefit from having more intensive monitoring and timely management of vomiting or nausea after their surgery. There are no notable risks involved with participating in this study.
Where is the study run from?
Clinica materno infantil San Luis (Columbia)
When is the study starting and how long is it expected to run for?
February 2014 to September 2016
Who is funding the study?
Industrial University of Santander (Columbia)
Who is the main contact?
Dr Rodolfo Parra Güiza
Prophylaxis of postoperative nausea and vomiting in cesarean section under spinal anesthesia with intrathecal morphine: controlled clinical trial comparing ondansetron vs placebo vs dexamethasone
Dexamethasone and Ondansetron are better than placebo for the prevention of nausea and vomiting in patients undergoing cesarean section under regional anesthesia and intrathecal morphine.
Institutional review board of the Clínica materno infantil San Luis (Colombia), 18/01/2014
Single-centre randomized placebo-controlled triple-blind trial
Primary study design
Secondary study design
Randomised controlled trial
Patient information sheet
No participant information sheet available
1. Postoperative nausea and vomiting
300 patients are randomized to one of three groups in a 1:1:1 ratio.
Ondansetron group: Participant receive 4 mg of ondansetron in 5 mL normal saline
Dexamethasone group: Participant receive 4 mg of dexamethasone in 5 mL normal saline
Placebo group: Participant receive 5 mL normal saline
In all groups, study drugs are administered at the time of lumbar puncture for the administration of the anesthetic-analgesic mixture (9 mg of bupivacaine + 25 micrograms fentanyl 100 micrograms of morphine) by the anesthesiologist responsible for the case.
Patients are evaluated intraoperatively, and then 2, 6 and 24 hours after intrathecal morphine. They are questioned about nausea and vomiting, need for rescue antiemetics, itching and pain using a numeric scale to indicate the severity of these symptoms (nausea, itching and pain). If patients have vomiting or severe nausea (numerical rating scale >7) postoperatively, they receive 4 mg of dexamethasone and 4 mg of ondansetron as antiemetic rescue therapy.
Ondansetron, Dexamethasone, Normal saline
Primary outcome measure
1. Incidence of nausea and vomiting is measured using a numerical rating scale (NRS) at 2, 6 and 24 hours after intrathecal morphine
2. Relative risk of nausea and vomiting by dividing the percentage cases of nausea and vomiting in the control group by the percentage cases in each of the intervention groups
3. Number needed to treat for nausea and vomiting is measured by the inverse of the Absolute Risk reduction (ARR) (% of cases of nausea on placebo group - % of cases of nausea on ondansetron or dexamethasone group) intraoperatively, at 2, 6 and 24 hours after intrathecal morphine
Secondary outcome measures
1. Incidence of pruritus is measured using a numerical rating scale (NRS) intraoperatively, at 2, 6 and 24 hours after intrathecal morphine
2. Relative risk of pruritus by dividing the percentage cases of pruritus in the control group by the percentage cases in each of the intervention groups
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
1. Pregnant patients scheduled for elective caesarean
2. Age between 18 - 40 years old
3. Spinal (Subarachnoid) anesthesia with intrathecal morphine
4. ASA Physical status 1-2
Target number of participants
Total final enrolment
Participant exclusion criteria
3. Kidney and/or liver failure
4. Known allergy to ondansetron or dexamethasone
5. Heart disease
7. Hyperemesis gravidarum
8. Nausea and vomiting or itching
9. Previous cesarean section
10. 5 HT3 antagonists or corticoids allergy
11. Gestational diabetes
13. Congenital long QT syndrome
14. Neurological or psychiatric illness that would prevent obtaining consent for the study Emergency Caesarean
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
Clinica materno infantil San Luis
Cra. 26 #48-56
Industrial University of Santander (Universidad Industrial de Santander)
Funding Body Type
Funding Body Subtype
Results and Publications
Publication and dissemination plan
Planned publication in a high-impact peer reviewed journal.
Intention to publish date
Participant level data
Available on request
Basic results (scientific)
2018 results [in Spanish] in https://revistas.uis.edu.co/index.php/revistamedicasuis/article/view/8190 (added 09/08/2019)