The goal of this clinical trial is to learn the effect of dexmedetomidine premedication in postoperative negative behavior changes in children compared to midazolam premedication. It will also learn about the effect of dexmedetomidine and midazolam in emergence delirium. The main questions are:

• Dose dexmedetomidine lower the incidence of postoperative negative behavior changes compared to midazolam?
• Dose dexmedetomidine lower the incidence of emergence delirium compared to midazolam? Researchers will compare dexmedetomidine to midazolam (a common pediatric premedication) to see if dexmedetomidine works to treat postoperative negative behavior change and emergence delirium.

Participants will:

• Take intranasal dexmedetomidine or oral midazolam or placebo (a look-alike substance that contains no drug) premedication
• Fill in the Post hospitalization behavior questionnaire for ambulatory surgery postoperative 1, 3, 7, and 30

Due to the fear of being separated from parents, fear of venipuncture, and facing unfamiliar operating room environment, children have different degrees of anxiety before surgery. Preoperative anxiety can lead to strong stress response and increase the incidence of emergence delirium. It can even cause psychological trauma and affect children's physical and mental health growth. The study showed that preoperative anxiety was positively correlated with the incidence of emergence delirium and postoperative negative behavior change, and emergence delirium was a risk factor for postoperative negative behavior in children.

Currently, midazolam is the most commonly used sedative drug to relieve preoperative anxiety in children. Midazolam has anterograde amnesia effect, reducing the occurrence of intraoperative awareness, and alleviating psychological trauma and memory of malignant stimulation in children. Dexmedetomidine is a highly selective α2 adrenergic agonist with anxiolytic, sedative, and analgesic properties. Our previous study found that preoperative administration of dexmedetomidine can reduce the incidence of emergence delirium in children compared with midazolam However, no clinical studies have directly compared the effects of dexmedetomidine and midazolam premedication on postoperative negative behavior change in children.

This prospective randomized controlled trial was conducted to compare the effects of dexmedetomidine and midazolam premedication on preoperative anxiety, the incidence of postoperative delirium, and postoperative negative behavior changes in children to provide a reference for optimizing clinical anesthesia medication regimens.

Inclusion Criteria:

1. ASA physical status I or II;
2. Aged 2-5 years;
3. Scheduled for elective tonsillectomy and (or) adenoidectomy.

Exclusion Criteria:

1. Parents refusing to allow their children to participate;
2. Intake of sedative or analgesic medication within 48 hours before surgery;
3. Developmental delay;
4. Psychosis;
5. Body mass index > 30 kg/m2;
6. Allergy to study drugs;
7. Major life changes 1 month before the operation, such as the divorce of parents, death of parents, moving to a new home, changing to a new kindergarten, etc.;
8. Any other conditions that precluded study inclusion.

After publication, the individual deidentified participant data underlying published results, the study protocol, and the statistical analysis plan can be accessed upon reasonable request from the corresponding author.

We would like to share our individual deidentified participant data beginning three months following the publication of the main results.

All the individual participant data collected during the trial, the study protocol, the statistical analysis plan, and the clinical study report can be accessed with approval from the corresponding author.