Clinical Characteristics and Outcomes of Very Old Critically Ill Patients in a Portuguese ICU: A Retrospective Cohort Study.

Introduction Patients aged ≥80 years represent a growing subgroup of intensive care unit admissions and frequently present with a high burden of multimorbidity and frailty. Frailty has consistently been associated with increased short- and long-term mortality in this population, often demonstrating stronger prognostic value than chronological age alone. However, data on long-term outcomes among frail very old patients in Portuguese intensive care units remain limited, particularly in the context of an aging population and potential resource constraints. Methods We conducted a single-center retrospective cohort study including all patients aged 80 years or older admitted to a polyvalent intensive care unit in Portugal between 2021 and 2023. Data collected included demographic characteristics, comorbidities assessed using the Charlson Comorbidity Index, number of daily prescription drugs, and frailty status assessed with the Clinical Frailty Scale, with patients classified as frail or non-frail. Illness severity at admission was evaluated using the Simplified Acute Physiology Score II, the Acute Physiology and Chronic Health Evaluation II score, and the Sequential Organ Failure Assessment score. Outcomes included the use of organ support therapies, decisions regarding life-sustaining treatment, lengths of stay in the intensive care unit and hospital, and survival at intensive care unit discharge, hospital discharge, and at one month, six months, and one year after discharge. Results Among 3,359 admissions, 328 (9.8%) patients were very old. The mean age was 83.9 years; 58.1% were male, and 35.1% were frail. Frail patients had a higher comorbidity burden (p<0.00001), greater medication use (p = 0.0019), and presented with higher Acute Physiology and Chronic Health Evaluation II scores, while Sequential Organ Failure Assessment and Simplified Acute Physiology Score II values were similar between groups. The use of organ support therapies and lengths of stay in the intensive care unit and hospital did not differ significantly. Intensive care unit and hospital mortality were comparable between frail and non-frail patients; however, long-term survival differed significantly, with lower one-year survival among frail patients compared with non-frail patients (47.0% versus 62.0%, p = 0.009). Conclusions Frailty was common among very old patients admitted to intensive care and, in unadjusted analyses, was associated with worse one-year survival, despite similar short-term mortality and resource utilization. Routine assessment of frailty may improve prognostication, support shared decision-making regarding life-sustaining treatments, and inform post-intensive care follow-up strategies tailored to this highly vulnerable population.