this study will aim to evaluate the effects of dexmedetomidine, dexamethasone and Ondansetron on the prevention of postoperative nausea and vomiting in children undergoing dental rehabilitation surgery.

Postoperative nausea and vomiting (PONV) is one of the most common and unpleasant postoperative complications, which is a major concern in surgical patients. PONV affects about 20-40% of surgical patients, with certain high-risk patients experiencing rates of up to 80%.

It has a high incidence in children, especially for tonsillectomy and dental surgery. PONV could lead to several adverse consequences, including dehydration, electrolyte imbalance, and wound dehiscence. it has also been reported PONV is associated with delayed hospital discharge, unplanned hospital admission, and increased financial costs required for patient care.

Several anti-emetic drugs have been described for the prophylactic control of PONV. Dexamethasone is common practice in surgery, as part of a multimodal pain and antiemetic strategy.

Ondansetron is a selective 5-HT3 receptor antagonist that exhibits an anti-emetic action by antagonizing vomiting signals in the afferent pathway from the stomach or small intestine and solitary tract nucleus and is effective at preventing PONV, however, the high cost of this drug has prevented it from being widely used.

Dexmedetomidine is a highly selective α2-adrenoreceptor agonist which has been widely used in clinical practice and has been explored extensively in the pediatric population due to its beneficial effects on perioperative morbidities. In the past few years, many studies in paediatrics have been published showing that dexmedetomidine lowered postoperative pain scores and opioid consumption, decreased the incidence of emergence agitation (EA), and improved the quality of recovery in pediatric patients undergoing different surgical procedures. In addition, a small selection of studies reported that dexmedetomidine could lower the incidence of nausea or vomiting after surgery and during the use of patient-controlled analgesia (PCA) in paediatrics. However, the effect of dexmedetomidine on PONV remains poorly understood.

In this study, investigators will evaluate the effect of dexmedetomidine on preventing postoperative nausea and vomiting in children in comparison with dexamethasone and ondansetron

Inclusion Criteria:

• Pediatric patients 6-12 years.
• Pediatric patients (ASA physical status I, II).
• Scheduled for dental rehabilitation surgery

Exclusion Criteria:

• Parental refusal
• Allergy or contraindication to studied medication or anaesthetic agents.
• Children with known gastroesophageal reflux disease.
• Intake of antiemetic medication within 24 hours before surgery.
• Past history or family history of previous postoperative nausea and vomiting.