Ciprofol is a novel intravenous anesthetic with a pharmacological profile similar to propofol but with a lower incidence of injection pain, hypotension, and respiratory depression. For pediatric day-case surgeries, laryngeal mask airway (LMA) insertion without neuromuscular blockers is increasingly preferred. While opioids are often combined with hypnotics to optimize insertion conditions, the optimal bolus dose of ciprofol when co-administered with a standard dose of fentanyl for LMA insertion in children remains unknown. This study aims to determine the 95% effective dose (ED95) of a single intravenous bolus of ciprofol, combined with a fixed dose of fentanyl (1 μg/kg), for successful LMA insertion in children aged 1-12 years during general anesthesia induction.

This is a prospective, single-blind (participant and outcomes assessor-blinded), biased-coin design up-and-down sequential allocation trial. A total of 180 pediatric patients (ASA I-II) scheduled for elective surgery requiring LMA insertion will be enrolled and divided into three age groups: toddlers (1-3 years), preschoolers (4-6 years), and school-age children (7-12 years), with 60 patients per group.

All patients will receive a fixed dose of fentanyl (1 μg/kg) and a predetermined bolus dose of ciprofol, administered intravenously over 1 minute. The initial ciprofol dose is set at 0.35 mg/kg, with a dose step size of 0.1 mg/kg. The dose for each subsequent patient is determined by the biased-coin design: if the previous patient achieves successful LMA insertion (no movement), the next patient receives the same dose with a probability of 0.947 or a 0.1 mg/kg lower dose with a probability of 0.053. If the previous patient fails (movement occurs), the next patient receives a 0.1 mg/kg higher dose.

The study employs a single-blind design: the anesthesiologist who administers the study drug is aware of the ciprofol dose, whereas the anesthesiologist who performs the LMA insertion and the observer who evaluates the patient's response are both blinded to the dose assignment. LMA insertion will be attempted 90 seconds after drug administration. Successful insertion is defined as the absence of jaw tightness, gross purposeful movement, coughing, gagging, or laryngospasm during LMA insertion and cuff inflation. The primary outcome is the ED95 of ciprofol for successful LMA insertion in each age group, estimated using isotonic regression with bootstrap resampling.

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) physical status I or II
• Aged 1 to 12 years
• Scheduled for elective surgery requiring general anesthesia with laryngeal mask airway (LMA) insertion (e.g., ophthalmic surgery, skin lesion excision, minor abdominal or urological procedures, with expected surgical duration ≤ 2 hours)
• Written informed consent obtained from parents or legal guardians

Exclusion Criteria:

• Known allergy or hypersensitivity to ciprofol, fentanyl, or any study-related drugs
• Intellectual disability, cognitive-affective disorders, psychiatric or neurological diseases
• Inability to cooperate with peripheral intravenous cannulation
• History of reactive airway disease or suspected difficult airway
• Body mass index (BMI) ≥ 30 kg/m² or ≤ 15 kg/m²
• History of sedative medication use
• Inability to understand the study protocol or participation in another clinical trial within the past 30 days