Urine urea nitrogen and 90 days mortality in long-stay critically ill patients on mechanical ventilation receiving enteral nutrition

Daily urinary urea nitrogen excretion has been proposed as a marker of hypercatabolism in critically ill patients. The aim of this study is to describe the association between urine urea nitrogen (UUN) and 90 days mortality in a cohort of long stay critically ill patients under invasive mechanical ventilation (IMV) receiving enteral nutrition (EN). Single center retrospective cohort study. Data from April 2021 to January 2023 were obtained from the Medical Information Picis database. Patients >18 years, with length of ICU stay ≥12 days, on IMV >5 days receiving EN >10 days were included with a follow-up until day 90. Patients with oliguric renal failure requiring continuous renal replacement therapy were excluded. UUN (g/day) from 24-h urine collection was measured between days 7 and 14 of ICU stay. UUN levels were divided into 3 groups: 1–10 g/day (mild hypercatabolism), 11–15 g/day (moderate hypercatabolism) and > 15 g/day (severe hypercatabolism) to assess the association between UUN and 90-day mortality. Different variables were analyzed including the medium caloric intake (Kcal/kg/d) (counting caloric intake from propofol), median protein intake (g/kg/d) and 90-day mortality. Categorical variables were summarized as frequencies and percentages and continuous variables as medians and interquartile ranges (IQR). Chi-square test was used to analyze 90-day mortality and analysis of variance to analyze the association between UNN and protein intake. 65 patients were included. The characteristics of the study population are shown in Table 1. Median caloric intake was 23 Kcal/kg/day [20–24] and median protein intake 1,1 g//kg/day [1,0-1,3]. 26% (n = 17) of the patients had UUN values between 1 and 10 g/day, 24% (n = 16) between 11 and 15, and 49% (n = 32) values >15 g/day. Total ICU mortality was 17%. Patients with UUN >15 g/day received a higher median protein intake when compared with group UUN:1–10 and UUN:11–15 (1,2, 1,09 and 1,06 g/kg/day respectively, p = 0,04). Global 90- day mortality was 31%. 90 day mortality was 35% in UUN:5–10 g/day, 37% in UUN: 11–15 d/day and 25% in UUN >15 g/day. There was no association between UUN value measured between days 7 and 14 of 24-h urine collection and 90-day mortality (p = 0,6). In this cohort of medical mechanically ventilated long-stay ICU patients we could not demonstrate any correlation between urine urea nitrogen and 90 day mortality. Patients with urine urea nitrogen >15 g/day received a higher median protein