1. The combined induction of intubation with propofol and remifentanil is widely used in clinical anesthesia, primarily through a single intravenous injection. Target-controlled infusion (TCI) technology, which combines pharmacology with clinical practice, offers a more stable and precise infusion mode;
2. This project aims to explore the half-effective concentration (EC50) of propofol combined with remifentanil for inhibiting tracheal intubation stimulation through a sequential approach under the monitoring of qNOX pain index.

Patients undergoing elective surgery, aged 19 to 55 years, with ASA I or II, were selected for a sequential trial in two stages:

1. In the first stage, induction dose of ciprofol was fixed at 0.4 mg/kg, and the EC50 and EC95 of remifentanil were measured.
2. In the second stage, the EC95 of remifentanil was fixed, and the EC50 and EC95 of ciprofol were measured. The EC and 95% confidence interval (CI) were calculated using the probit probability unit method.
3. Additionally, the effectiveness of the qNOX index in guiding tracheal intubation stimulation was evaluated by analyzing the receiver operating characteristic (ROC) curves.

Inclusion Criteria:

• Patients scheduled for elective surgery and require general anesthesia with single-lumen endotracheal intubation: ASA physical status I-II, aged between 18 and 55 years, with a body mass index (BMI) between 18.5 and 30 kg/m2

Exclusion Criteria:

• 1.Emergency surgery patients, children, pregnant women; 2.Patients with unstable vital signs: such as blood pressure, heart rate, and blood oxygen saturation exceeding the safe range; 3.Patients with craniocerebral trauma or central nervous system lesions; 4.Patients who are allergic to the studied anesthetic drugs, or have recently received other experimental drugs, major surgery, radiotherapy, or chemotherapy; 5.Patients who refuse to sign the informed consent form.

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