Associations of early postoperative anemia with mortality and ICU outcomes in nonagenarians and centenarians undergoing colorectal cancer surgery: a binational multicenter propensity matching study.

INTRODUCTION: Colorectal cancer (CRC) disproportionately affects older adults, with nonagenarians and centenarians representing a rapidly growing surgical population. Anemia is highly prevalent after CRC surgery and may worsen outcomes, yet its prognostic significance in the oldest old remains unclear. We aimed to evaluate whether early postoperative anemia was associated with mortality and intensive care unit (ICU) outcomes in nonagenarians and centenarians undergoing CRC surgery. METHODS: We conducted a retrospective cohort study using the Australian and New Zealand Intensive Care Society Adult Patient Database, including patients ≥ 90 years admitted to the ICU after CRC surgery between 2010 and 2024. Early postoperative moderate-to-severe anemia was defined as hemoglobin ≤ 110 g/L within 24 h after ICU admission. Propensity score matching (1:1) was used to balance demographic and clinical characteristics. The primary outcome was all-cause mortality; secondary outcomes included ICU and hospital length of stay (LOS), acute renal failure (ARF), and need for invasive mechanical ventilation. Cox regression, logistic regression, and linear models were applied as appropriate. RESULTS: A total of 1,080 patients were included after matching (540 per group). Moderate/severe anemia was independently associated with increased all-cause mortality (hazard ratio [HR] 1.26; 95% CI, 1.03-1.55; p = 0.029). Additional mortality predictors included older age, male sex, and higher APACHE III scores. Anemia severity was not significantly associated with ICU or hospital LOS, ARF, or early invasive ventilation. In contrast, elective surgery consistently predicted shorter ICU and hospital stays and lower complication rates compared with non-elective surgery. DISCUSSION: In this large, multicenter cohort of nonagenarians admitted to intensive care after surgery, early postoperative anemia was common and independently associated with higher mortality. While anemia did not significantly influence ICU or hospital length of stay or major complications, patients with moderate to severe anemia had a sustained increase in mortality risk even after propensity score matching. These findings underscore the prognostic value of anemia in the immediate postoperative period and support its consideration in risk stratification and long-term follow-up of the oldest surgical patients.