Mediation of postoperative length of stay by major adverse cardiovascular events in elderly patients underwent major thoracic and abdominal surgery receiving peripheral nerve blocks

BACKGROUND: The association between preoperative peripheral nerve block (PNB), major adverse cardiovascular events (MACE), and postoperative length of hospital stay (LOS) in elderly patients who underwent major thoracic and abdominal surgery remains unclear. This study aims to explore the potential mediating effect of MACE on the association between preoperative PNB and postoperative LOS using a statistical mediation framework. METHODS: In this retrospective cohort study, perioperative data were collected from elderly patients (aged over 65 years) who underwent major thoracic and abdominal surgery. Mediation analysis was employed to examine the relationships between PNB, MACE, and postoperative LOS. RESULTS: A total of 1915 patients were included in the analysis, with 68.7% (1316/1915) receiving preoperative PNB. Compared to patients who did not receive PNB, those who did had a significantly lower incidence of MACE (P < 0.001) and a shorter postoperative LOS (P < 0.001). The adjusted total and direct associations of PNB with postoperative LOS were - 0.809 days (95% confidence interval [CI], -1.236 to -0.390; P < 0.001) and - 0.661 days (95% CI, -1.077 to -0.250; P = 0.003), respectively. A statistically significant indirect association via MACE was observed (adjusted β=-0.149 days; 95% CI, -0.271 to -0.060; P < 0.001), indicating that 18.1% (95% CI, 6.7% to 41.0%) of the total association was statistically attributable to the indirect pathway through MACE under the model assumptions. A sensitivity analysis excluding postoperative covariates yielded consistent results (proportion mediated: 25.3%). CONCLUSIONS: Our findings suggest that the observed association between preoperative PNB and reduced postoperative LOS in elderly patients following major thoracic and abdominal surgery may be partly explained by a statistically significant indirect pathway through a reduction in MACE, potentially accounting for approximately 18% of the total effect. These findings are hypothesis-generating and represent statistical associations rather than demonstrated causal mechanisms. TRIAL REGISTRATION: ChiCTR2400087610; https://www.chictr.org.cn.