Patients received taVNS treatment immediately upon entering the AICU, with sessions occurring every 2 hours. A specialized taVNS stimulator device was used, and the left ear was cleaned with an alcohol swab or wet tissue before inserting an earplug with electrode contacts into the left ear, ensuring a snug fit. A second earplug was inserted into the right ear. The stimulation parameters were set as follows: continuous wave, frequency 20 Hz, pulse width 200 μs. Each treatment session lasted for 30 minutes.

The treatment protocol was identical to that of the taVNS group. Electrodes were placed on the left auricle. After the device was activated, it either did not deliver any current or only emitted a brief sub-threshold current to simulate the sensation of device activation, without producing continuous neural stimulation.

Patients received taVNS treatment immediately upon entering the AICU, with sessions occurring every 2 hours. A specialized taVNS stimulator device was used, and the left auricle was cleaned with an alcohol swab or wet tissue before inserting an earplug with electrode contacts into the left ear, ensuring a snug fit. A second earplug was inserted into the right ear. The stimulation parameters were set as follows: continuous wave, frequency of 20 Hz, and pulse width of 200 μs. Each treatment session lasted for 30 minutes.

Total consumption of opioids (morphine equivalent) within 24 hours postoperatively.

Postoperative first-night sleep quality score (Richards-Campbell Sleep Questionnaire, RCSQ); the score ranges from 0 to 150, with higher scores indicating better sleep quality.