The study was under the approval of the Ethic Committee of The First Hospital of Hebei Medical University (approval number: 2023-00036), and the patients gave written informed consent.

Obese patients undergoing elective laparoscopic surgery under general anesthesia were selected for our experiment. Inclusion criteria: age 18–65 years, ASA class II or III, 30 kg/m2 ≤ body mass index (BMI) < 40 kg/m2, and unlimited gender. Exclusion criteria: patients with anticipated difficulty in mask ventilation and obstructive sleep apnea syndrome; those with severe cardiopulmonary, hepatic, and renal diseases; those with alcoholism, drug abuse, and long-term use of sedative and analgesic drugs; those with psychiatric disorders and those who were unable to cooperate; those with a third-degree atrioventricular block with an entry heart rate (HR) < 50 beats/min. On the basis of the random number table method, patients were randomly separated into 2 groups (n = 30): the control group (group C) and the dexmedetomidine group (group D). The trial participants, anesthetists, staff collecting data, and laboratory staff were blinded to the group assignments.

Patients underwent routine preoperative fasting. Upon entering the operating room, an intravenous cannula was sited in the upper limb, and pulse oximetry, electrocardiogram, and noninvasive blood pressure were tested. The arterial pressure was measured by direct puncture of the radial artery under local anesthesia with lidocaine. Patients in group D were given dexmedetomidine hydrochloride (1 μg/kg lean body weight (LBW) (calculated as (9270 × body weight)/(6680 + 216 × body weight/height2) for males and (9270 × body weight)/(8780 + 244 × body weight/height2) for females) 10 min before anesthesia induction, which was subsequently infused at a rate of 0.5 mg/kg h (LBW) until 30 min before the end of the operation, and patients in group C were infused with an equal volume of saline in the same way. Induction of anesthesia: midazolam 0.05–0.1 mg/kg (LBW), sufentanil 0.5–1.0 μg/kg (LBW), propofol 1–2 mg/kg (LBW), and rocuronium bromide 0.6–0.9 mg/kg (LBW) were intravenously injected for 2 min, and then tracheal tube was inserted, to make sure that tracheal tube was correctly positioned, and then connecting to the anesthesia machine to carry out mechanical ventilation. We adopted a volume-controlled mode of ventilation, maintaining a low tidal volume of 6–8 ml/kg LBW, a ventilation frequency of 12–14 times/min, an inhalation to exhalation ratio (I: E) of 1: 2, and a positive end-expiratory pressure (PEEP) of 5 cmH2O (1 cmH2O = 0.098 kPa). The pressure of end-tidal carbon dioxide (ETCO2) was maintained between 35 and 45 mmHg (1 mmHg = 0.133 kPa) by adjusting the respiratory rate. Anesthesia was maintained with propofol 6–8 mg/kg h (LBW), remifentanil 0.1–0.5 μg/kg·min (LBW), and intermittent bolus injection of rocuronium for maintaining muscle relaxation. Ten minutes after general anesthesia was stabilized, CO2 was injected into the abdominal cavity (pneumoperitoneum pressure 12 mmHg). Intraoperative fluctuations in mean arterial pressure (MAP) were maintained at no more than 20% of the basal value, and the bispectral index (BIS) value was between 40 and 60. If intraoperative hypotension or bradycardia occurred in the patient, the appropriate cardiovascular active drugs (phenylephrine or atropine) were administered.

The patients were transported to the PACU after the operation. All patients were extubated after receiving an intravenous sugammadex injection at 2 mg/kg of LBW. All patients were evaluated by the anesthesiologist in the PACU and returned to the ward by the nurse anesthetist after meeting the PACU discharge criteria.

The surgical time points were divided into: before anesthesia induction (T0), 5 min after intubation (T1), 30 min after pneumoperitoneum (T2), 10 min after pneumoperitoneum release (T3), at the time of extubation (T4), 3 min after extubation (T5), and 24 h after surgery (T6). At four time points T1, T2, T3, and T4, radial artery blood was taken for blood gas analysis, and arterial partial pressure of oxygen (PaO2), arterial partial pressure of carbon dioxide (PaCO2) values were recorded. Dynamic lung compliance (Cdyn) (calculated as = tidal volume/(peak inspiratory pressure—positive end-expiratory pressure), oxygenation index (OI) (calculated as PaO2/FiO2), alveolar-arterial oxygen partial pressure difference (A-aDO2) (FiO2[PB − PH2O] − [PaCO2/R]) − PaO2, PB was the barometric pressure (760 mmHg at sea level); and PH2O was the water vapor pressure (47 mmHg when air is fully saturated at 37 ℃)), and respiratory index (RI) (calculated as P(A-a)O2/PaO2) was calculated based on the formula. The surgery time, anesthesia time, CO2 pneumoperitoneum time, eye-opening time, and time from the end of surgery to extubation were recorded. Radial artery blood was taken from T0 to T6, let stand for 30 min, and centrifuged at 3000 r/min for 10 min, and the supernatant was taken and stored at − 70 ℃. Plasma IL-8 and IL-10 concentrations were measured by enzyme-linked immunosorbent assay. The reagent kit was purchased from ACROBiosystems (Beijing, China), and the operating procedures strictly followed the instructions of the reagent kit.

The sample size was determined to study a clinically relevant difference between the two groups with regard to the primary outcome variable. The primary outcome was dynamic lung compliance (Cdyn). Preliminary estimates put the number of cases in each group at 25 (with a two-sided 5% significance level and 80% statistical power). Considering the influence of shedding and elimination (20%), the overall sample size was set as 60 cases, 30 cases in the dexmedetomidine group (group D), and 30 cases in the control group (group C).

The Statistical Package for Social Science (SPSS) software, version 26 for Microsoft Windows (SPSS Inc, Chicago, IL, USA), was used for the data analysis. Measurement data were tested for normality using the Shapiro–Wilk test and were depicted as mean ± standard deviation. The t-test was utilized for inter-group comparison. A repeated-measures analysis of variance and the Bonferroni post-hoc pairwise comparison tests were used to assess the changes at the different time points. Numeration data were expressed as number (n) and compared by implementing the χ2 test. Two-sided P < 0.05 was considered a statistically significant difference.