General anesthesia is the preferred choice for pediatric patients, but the induction of volatile anesthetics via face mask may cause preoperative anxiety and postoperative delirium. Total intravenous anesthesia (TIVA) is more suitable for pediatric patients, as it can effectively alleviate preoperative anxiety, reduce the risk of postoperative delirium and mania, shorten hospital stay, reduce medical burden, and increase parental satisfaction. Propofol, although effective for anesthesia, has drawbacks such as injection pain and respiratory and circulatory suppression. Remimazolam is a novel ultra-short-acting benzodiazepine drug, which has no injection pain, minimal impact on respiration and circulation, and rapid onset and elimination, making it suitable for children. However, research on remimazolam in children is limited. This study aims to compare the effect of propofol and remimazolam intravenous anesthesia combined with regional or caudal block on respiratory depression in preschoolers.

Ninety-six children aged 3-6 years scheduled for surgery under general anesthesia were randomly divided into two groups. Initially, fentanyl was administered at a dose of 2-3 mcg/kg, and after 3 minutes, different test drugs were given according to the group assignment. In group P, propofol was administered intravenously at a dose of 2.0 mg/kg, while in group R, remimazolam was administered intravenously at a dose of 0.45-0.55 mg/kg. After achieving loss of consciousness (LoC, MOAA/S ≤ 1), a laryngeal mask was inserted, and spontaneous breathing was maintained. Subsequently, the test drugs were infused according to the group assignment, and both groups received a constant infusion of remifentanil at a rate of 0.05-0.4 μg/kg/min. After connecting the micro-infusion pump, regional or caudal block was performed. Once the local anesthetic had taken full effect, the infusion of remifentanil was stopped, and surgery began. The test drugs were stopped approximately 5 minutes before the end of the surgery, and the laryngeal mask was removed when spontaneous breathing reached a tidal volume of ≥ 6 ml/kg and a frequency of ≥ 15 breaths per minute.

The following data were recorded: the time to loss of consciousness, the incidence of respiratory depression during anesthesia, the success rate of intravenous sedation, the incidence of postoperative agitation, recovery time, MOAA/S scores, and vital signs such as heart rate, blood pressure, and pulse oximetry.

Inclusion Criteria:

1. Aged 3-6 years, gender unrestricted;
2. American Society of Anesthesiologists (ASA) physical status classification of I-II;
3. Body Mass Index (BMI) between 14 kg/m² and 25 kg/m²;
4. Patients requiring elective surgery that can be completely anesthetized through regional or caudal block;
5. The child's parent or legal guardian voluntarily participates in this trial and signs the informed consent form.

Exclusion Criteria:

1. Children requiring special care or under the supervision of a court or social welfare agency;
2. Children who have received general anesthesia within 3 months prior to the screening period;
3. Children with a history of respiratory diseases within the past 2 weeks or those deemed to have difficult airway management: Modified Mallampati score of III or IV;
4. Children with severe cardiovascular diseases or endocrine system abnormalities;
5. Children with known psychiatric disorders or cognitive impairments;
6. Children with abnormal liver function, ALT (alanine aminotransferase) and/or AST (aspartate aminotransferase) >1.5 times the upper limit of normal; children with total bilirubin exceeding the upper limit of normal; children with abnormal kidney function, creatinine and/or blood urea nitrogen higher than the upper limit of normal;
7. Children known or suspected to be allergic to the study drug or benzodiazepines.