Effect of Intraoperative Dexmedetomidine on Postoperative Pain in Elderly Patients Undergoing Major Abdominal Surgery: a Secondary Analysis Based on Prospective Data

This study is a secondary analysis of multicenter prospective data, including elderly patients who underwent elective major abdominal surgery between April 2020 and April 2022 from a perioperative database of elderly patients in China. In this study, we specifically extracted and analyzed the data at the 3-month follow-up time point after abdominal major surgeries in elderly patients to evaluate the association between the intraoperative use of dexmedetomidine and postoperative chronic pain (CPSP) in this elderly patient population.

Exposure definition: Patients who received dexmedetomidine (dose range 0.2-1.0 μg/kg·h) for anesthesia induction or maintenance during the operation were defined as exposed, while those who did not receive it were the unexposed group.

Primary outcome: The primary outcome was the incidence of postoperative pain at 3 months, assessed using the Brief Pain Inventory (BPI).

Secondary outcomes: Secondary outcomes included pain severity, pain interference score, and health-related quality of life at 7 days, 1 month, and 3 months after surgery. Pain indicators were evaluated using the Brief Pain Inventory (BPI), and health-related quality of life was assessed using the EQ-5D-5L scale.

Statistical analysis: Missing covariates were handled using multiple imputation (m = 25), and potential confounders were controlled using inverse probability weighting (IPTW). Considering hospital clustering, all regression models had hospital as a random effect. A weighted logistic regression model was used to assess the impact of dexmedetomidine on the incidence of pain, a log-linear model was used to analyze pain severity scores and pain interference scores, and a linear mixed-effects model was used to analyze changes in health-related quality of life at the three time points after surgery.

Sample size and statistical power: Sample size estimation was based on previous literature. A prospective cohort study of patients undergoing gastrointestinal surgery showed that the incidence of chronic pain 3 months after surgery was 30.58% . Based on the results of a meta-analysis , the incidence of chronic pain 3 months after surgery in patients using dexmedetomidine was estimated to be reduced to 15.6%. Based on the distribution of patients meeting the inclusion and exclusion criteria in the database, the sample size ratio between the treatment group and the non-treatment group was approximately 1:2. Using PASS 2021 software, continuity correction was set, and under the two-sided test level α = 0.05 and test power 1 - β = 0.80, 251 patients (84 in the treatment group and 167 in the non-treatment group) were required. Considering a 20% dropout rate, the total sample size should be at least 314 cases (105 in the treatment group and 209 in the non-treatment group).

Data processing and quality control: All data will be extracted by trained researchers from the database.

Ethical considerations: Since this study only conducts a secondary analysis of anonymized existing data, the ethics committee waived the requirement for obtaining additional written informed consent from the participants. This study will be conducted in accordance with the Helsinki Declaration and relevant local regulations.

Inclusion criteria

• Age ≥ 65 years;
• Underwent elective gastrointestinal and hepatobiliary surgeries.

Exclusion criteria

• Patients with ASA grade IV or above;
• Patients with missing exposure factor data;
• Patients without postoperative pain assessment data;
• Patients transferred to the ICU after surgery or who died within 7 days after surgery.