Postoperative enteral nutrition timing and risk variation in elderly patients with perforated peptic ulcer.

PURPOSE: Enteral nutrition (EN) is important for postoperative recovery in elderly patients with perforated peptic ulcer (ePPUs), but the optimal initiation timing remains unclear. This study aimed to analyze the association between EN timing and adverse outcome in ePPUs. METHODS: This retrospective cohort study enrolled 142 ePPUs who underwent surgical repair between May 2017 and May 2025. Postoperative outcomes were stratified using a two-step clustering (TSC) model. Subsequently, machine learning was further applied to evaluate how the risk of adverse outcomes varied with delayed enteral nutrition initiation. RESULTS: Among 142 patients, 104 were classified into the NAOG and 38 into the AOG. Compared with the NAOG, the AOG showed higher rates of intra-abdominal infection (86.8% vs. 0.0%, p < 0.001) and anastomotic leakage (23.7% vs. 0.0%, p < 0.001), longer hospital stay (22.50 [15.00-34.50] vs. 9.50 [8.00-12.25] days, p < 0.001) and ICU stay (106.50 [0.00-308.00] vs. 0.00 [0.00-0.00] hours, p < 0.001). Meanwhile, the AOG had higher preoperative serum creatinine levels (130.50 [85.00-192.50] vs. 83.50 [64.00-107.00] μmol/L, p < 0.001) and larger perforation sizes (10.00 [7.25-15.00] vs. 8.00 [5.00-10.00] mm, p < 0.001). In the primary DML analysis, each 1-day delay in postoperative EN initiation was associated with a 3.55% (95% CI, 1.41-6.61%) increase in adverse outcome risk. Postoperative day 6 corresponded both to the point at which the spline-based risk residual returned to zero and to the cutoff with the highest AUC in the decision-tree analysis (AUC = 0.724). CONCLUSION: Delayed postoperative EN initiation was associated with a cumulative increase in adverse outcome risk, which appeared to shift to a higher-risk level after approximately postoperative day 6.