This clinical study was reviewed and approved by the Ethics Committee of Cangzhou Central Hospital (2021-206-02 (z)). Before conducting the study, the patients and their families were fully informed and signed an informed consent form. Patients aged 60–75 years with a body mass index (BMI) of 18.5–23.9 kg/m² were selected for unilateral radical mastectomy between January 2023 and December 2023. ASA I or II, with no visual or hearing impairments.

Patients were excluded if they met any of the following criteria: refusal to sign informed consent, long-term use of analgesics, recent use of anesthetics and psychiatric drugs, history of alcohol and drug abuse, liver and kidney dysfunction, electrolyte disturbance, concomitant diseases of other important organs, contraindication to inhaled anesthetics, and family history of malignant high fever.

Inclusion criteria for patients with mild cognitive impairment: (1) Minimum Mental State Examination (MMSE) < 27; (2) Montreal Cognitive Assessment (MoCA) < 26 [11].

Inclusion criteria for patients with sleep disorders: (1) Pittsburgh Sleep Quality Index [12] (PSQI) ≥ 7; (2) Epworth Sleepiness Scale [13] (ESS) ≥ 10.

All patients were strictly fasted before surgery. Upon entering the room, the individual inhaled oxygen through the mask, established peripheral venous access, and infused lactated Ringer’s solution at a rate of 10 ml/kg. Non-invasive blood pressure (NIBP), electrocardiogram (ECG), pulse oxygen saturation (SPO2), end-tidal carbon dioxide concentration (ETCO2), and nasopharyngeal temperature were monitored. Sevoflurane was used for anesthesia induction. The sevoflurane volatile tank scale was adjusted to 8%, the oxygen flow rate was set to 6 L/min, and the anesthesia circuit was pre-filled. At the beginning of the induction, the mask was tightly fastened to the patient’s face, and the patient was instructed to take deep breaths. After the patient lost consciousness, their jaw relaxed, and a laryngeal mask was inserted for mechanical ventilation. Tidal volume was 6–8 ml/kg, respiratory rate 10–12 breaths/min, inspiratory/expiratory ratio 1:2, oxygen flow 2 L/min, and ETCO2 was maintained at 30–40 mmHg. Bispectral index (BIS) was used in all patients to maintain BIS values between 40 and 60.

In this study, the Dixon up-and-down method was used to set the end-tidal sevoflurane concentration of the first patient in each group to 2.2%. When the concentration reached the set value and remained stable for at least 15 min, the skin incision was initiated. Conversely, if a body movement response was recorded as positive, the end-tidal sevoflurane concentration was increased by 0.2% in the next patient. The midpoint between a negative reaction and the first subsequent positive reaction was recorded as the equilibrium point. According to the Dixon up-and-down method guidelines [14], we randomly assigned patients to groups for experiments. The experiment concluded when there were 7 equilibrium points, ensuring that the number of patients in each group exceeded twenty.

Three milliliters of venous blood were collected from the patient before the surgery. The blood was then centrifuged at 3,000 rpm for 15 min, and the upper layer of serum was collected post-centrifugation. The serum was stored in a refrigerator at -80 °C. Serum melanin-concentrating hormone concentrations were determined by Elisa kits (Cusabio Biotechnology Co., China).

SPSS 26.0 statistical software was used for data analysis. Measurement data following normal distribution were presented as mean ± standard deviation (x¯±s), and a two-sample t-test was employed to compare between groups. Non-normally distributed measurement data were expressed as median (M) and interquartile range (IQR). The MAC value and the 95% confidence interval (CI) of sevoflurane were calculated by the probit analysis. Logistic regression was conducted to test the correlation of probability of MAC and melanin-concentrating hormone. P < 0.05 was considered statistically significant.