The Interplay among Respiratory Failure, Delirium, Frailty and Severity of Illness in Hospitalized Older Medical Patients: A Nationwide Multicenter Observational Study.

Background: Prevalence, correlates and outcomes of respiratory failure (RF) were never studied in large populations of older patients hospitalized in acute care medical settings. Little is known about the possible association between RF and delirium, and whether these two syndromes, alone or in combination, may affect short-term mortality.

Objectives: To investigate prevalence and features of RF, the association between delirium and RF, and their effect on short-term mortality.

Design: Prospective cross-sectional study with data collection on an index day and 30-day follow up.

Setting and participants: 1493 patients aged ≥ 65 years hospitalized in Italian acute medical wards from the 2017 Delirium Day database.

Methods: RF was identified according to the detection of peripheral oxygen saturation ≤ 91% on the index day, or to ongoing oxygen therapy or non-invasive ventilation on the index day or the day before. A modified National Early Warning Score (NEWS), obtained removing the "Oxygen Saturations" and "Any Supplemental Oxygen" items, measured non-hypoxemic severity of acute illness.

Results: 300 patients (20.1%) had RF. Mortality was 16.6% in the RF group and 8.2% in the non-RF group (p<0.001). Delirium prevalence was 31.3% in RF (94 patients, 72 of whom with hypoactive or mixed delirium) and 22% in non-RF patients (p<0.001). Age, frailty, modified NEWS, steroids use, presence of urinary catheters or other major devices, but not delirium, were independent RF correlates. RF alone (OR [odds ratio]: 1.83; 95% CI [confidence interval]: 1.02-3.29) predicted 30-day mortality after adjustment for confounders, including modified NEWS. Without adjustment for modified NEWS, the combination of delirium and RF also significantly predicted 30-day mortality (OR: 2.26; 95% CI 1.08-4.72).

Conclusions: In hospitalized older medical patients, RF was a prevalent syndrome which was frequently complicated by delirium. RF was featured by older age, frailty and severe illness, and independently predicted short-term mortality.