When Winter Comes: Seasonal Patterns in Outcomes After Major Surgery

Introduction Seasonal strain may affect perioperative care, yet national evidence on seasonal variation in outcomes after major surgery remains limited. We evaluated whether postoperative outcomes varied by season among older adults undergoing major surgical procedures. Methods Medicare beneficiaries aged 65 y or older undergoing abdominal aortic aneurysm repair, coronary artery bypass grafting, colectomy, lung resection, or pancreaticoduodenectomy from 2016 through 2021 were identified using 100% Medicare Standard Analytic Files. Seasons were defined meteorologically, with spring as the reference. Outcomes included 30-d mortality, 90-d mortality, complications, textbook outcome, failure to rescue, surgical site infection, and length of stay. Multivariable regression models adjusted for patient, procedure, and hospital characteristics and were stratified by elective versus emergency admission. Interactions with the nurse-to-bed ratio and the Centers for Medicare & Medicaid Services Hospital Star Rating were assessed. Results Among 1,165,265 patients, 738,236 underwent elective surgery and 427,029 underwent emergency surgery. Among emergency admissions, winter was associated with higher adjusted odds of 30-d mortality (adjusted odds ratio: 1.10; 95% confidence interval: 1.07-1.13), 90-d mortality (1.10; 1.07-1.13), complications (1.05; 1.03-1.07), and failure to rescue (1.11; 1.07-1.15), as well as lower odds of textbook outcome (0.96; 0.94-0.98) and longer length of stay. Among elective admissions, winter was associated with smaller increases in 30-d and 90-d mortality. No significant interaction was observed by nurse-to-bed ratio or Centers for Medicare & Medicaid Services Hospital Star Rating. Conclusions Winter was associated with worse outcomes after major surgery, particularly among emergency admissions, supporting targeted seasonal preparedness strategies.