This is a prospective, single-center, randomized, double-blind controlled trial involving patients scheduled for elective surgery requiring general anesthesia with propofol induction. Participants are randomly assigned to one of three groups: the ondansetron group (8 mg IV), the lidocaine group (40 mg IV), or the control group (0.9% normal saline placebo). Study medications are administered intravenously over 5 minutes, ending 1 minute before anesthetic induction.

the goal: To assess the efficacy of intravenous ondansetron versus lidocaine and placebo in reducing the incidence and intensity of pain associated with propofol injection in patients undergoing general anesthesia.

This prospective, single-center, randomized, double-blind controlled trial is conducted at the operating theaters of the Mongi Slim University Hospital (Tunisia). The study aime to compare the effectiveness of intravenous ondansetron and lidocaine versus placebo in preventing pain associated with propofol injection during induction of general anesthesia.

Adult patients (ASA I-III) scheduled for elective surgery requiring propofol-based induction are randomly allocated in a 1:1:1 ratio to receive either ondansetron 8 mg, lidocaine 40 mg, or normal saline placebo before anesthesia induction. The primary outcome is the incidence of pain during propofol injection, while secondary outcomes include pain intensity, postoperative nausea and vomiting, patient satisfaction, and pain recall.

A total of 156 patients are planned for inclusion. Pain is assessed immediately after administration of an initial propofol bolus using a numerical rating scale (0-10) by a blinded observer. The study is designed to determine whether ondansetron could provide analgesic efficacy comparable to the current standard treatment, lidocaine, while also offering potential benefits related to the prevention of postoperative nausea and vomiting.

Inclusion Criteria:

• The study included patients who met all of the following criteria:

Aged 18 years or older; Classified as ASA physical status I-III (Appendix 1); Provided written informed consent to participate in the study; Scheduled for elective surgery requiring general anesthesia with propofol induction.

Exclusion Criteria:

• Patients were not eligible for inclusion if they:

Had received analgesics or antiemetics within 12 hours before surgery; Had communication difficulties or were unable to assess pain adequately (e.g., language barrier, dementia, impaired consciousness); Had a known allergy to ondansetron, lidocaine, or propofol; Did not receive propofol for anesthetic induction; Were pregnant or breastfeeding; Suffered from chronic pain or regularly used opioid medications; Did not have a 20-gauge intravenous catheter inserted on the dorsum of the hand; Declined participation in the study.

Patients were excluded from the study if they experienced any complication during anesthetic induction, including:

Anaphylactic shock or allergic reaction to study medications; Hemodynamic or respiratory instability.

Patients who subsequently withdrew their consent were also excluded from the study.