Early anaemia and prognosis after knee arthroplasty in nonagenarians admitted to ICU post surgery: a multicentre binational cohort study

Abstract

Introduction Anaemia is one of the most common complications following major surgery, arising from perioperative blood loss, hemodilution, and impaired erythropoiesis. Although preoperative anaemia is a recognised risk factor for adverse outcomes, the prognostic importance of early postoperative anaemia remains underexplored, particularly in very elderly patients. Given the rising prevalence of osteoarthritis and total knee arthroplasty (TKA) in the >= 90-year-old population, understanding the implications of anaemia in this high-risk cohort is increasingly relevant. Methods We conducted a retrospective binational cohort study using the Australian and New Zealand Intensive Care Society (ANZICS) Adult Patient Database. All patients >= 90 years admitted to the ICU following TKA between 2010 and 2024 with haemoglobin (Hb) measured within 24 h were included. Anaemia was defined according to World Health Organization criteria and stratified as non-anaemia, mild, or moderate/severe. The primary outcome was all-cause mortality, examined in short-term (< 365 days) and long-term (>= 365 days) intervals. Secondary outcomes included ICU and hospital length of stay (LOS), illness severity scores, and postoperative biochemical and physiological parameters. Time-to-event outcomes were assessed with Cox regression, and LOS outcomes with log-transformed linear models. Results Among 493 patients, 22.3% were non-anaemic, 30.0% had mild anaemia, and 47.7% had moderate/severe anaemia. Severe anaemia was associated with higher illness severity (median APACHE III 57 vs 54; p = 0.013), prolonged ICU stay (18% longer; p = 0.008), and longer hospitalisation (p = 0.037). Anaemia was not associated with short-term mortality. However, beyond 365 days, both mild (HR 2.08; 95% CI 1.05-4.13; p = 0.036) and severe anaemia (HR 1.98; 95% CI 1.05-3.73; p = 0.035) independently predicted higher mortality. Discussion/conclusion In nonagenarians undergoing TKA, anaemia at ICU admission was highly prevalent and associated with increased illness severity, resource utilisation, and elevated long-term mortality. These findings highlight postoperative Hb as an important prognostic marker in the oldest old and support strategies for early detection, optimisation, and structured follow-up to improve survival and recovery in this vulnerable population.