Geographic differences in outcomes after emergency surgery in nonagenarians and centenarians admitted to intensive care in Australia: a population-based study

Nonagenarian and centenarian patients increasingly undergo emergency surgery with subsequent intensive care unit (ICU) admission, but it remains unclear whether geographic disparities in outcomes arise during the index hospitalization or emerge after discharge in universal health systems. We conducted a national, population-based retrospective cohort study using linked data from the Australian and New Zealand Intensive Care Society (ANZICS) Adult Patient Database and the Australian National Death Index. We included all nonagenarian and centenarian patients admitted to Australian ICUs after emergency surgery between January 1, 2018, and December 31, 2024. Geographic residence on ICU admission was classified with the Modified Monash Model as metropolitan (MMM1) or regional/remote (MMM2–7). Outcomes were ICU mortality, in-hospital mortality, and all-cause post-discharge mortality at 5 years among patients discharged alive. Cox proportional hazards regression was used to examine associations between geographic residence and post-discharge mortality, with adjustment for age, sex, Acute Physiology and Chronic Health Evaluation (APACHE) III score, Sequential Organ Failure Assessment (SOFA) score, major chronic comorbidities, and hospital type. Among 4,887 patients admitted to ICUs after emergency surgery, ICU and hospital mortality did not differ meaningfully by geographic residence. In contrast, among patients discharged alive, regional or remote residence was independently associated with higher post-discharge mortality at 5 years (adjusted HR, 1.133, 95% CI 1.027–1.250, p = 0.013) compared with metropolitan residence. Survival curves diverged after hospital discharge and remained separated throughout follow-up. In a secondary cohort of 7,896 patients undergoing elective surgery, geographic residence was not associated with ICU, in-hospital, or post-discharge mortality. Among nonagenarian and centenarian patients admitted to ICUs after emergency surgery, geographic residence was not associated with mortality during the index hospitalization but was independently associated with higher long-term mortality after discharge. While no differences were observed during the acute care episode, patients residing in regional or remote areas experienced lower post-discharge survival compared with those living in metropolitan areas. These findings highlight potential geographic variation in long-term outcomes and support further investigation into factors influencing post-discharge care and survival among the oldest surgical patients.