Association between the ROX index and mortality in patients with acute hypoxemic respiratory failure: a retrospective cohort study

Abstract

Background: Although ROX index is frequently used to assess the efficacy of high-flow nasal cannula treatment in acute hypoxemic respiratory failure (AHRF) patients, the relationship between the ROX index and the mortality remains unclear. Therefore, a retrospective cohort study was conducted to evaluate the ability of the ROX index to predict mortality risk in patients with AHRF.

Method: Patients diagnosed with AHRF were extracted from the MIMIC-IV database and divided into four groups based on the ROX index quartiles. The primary outcome was 28-day mortality, while in-hospital mortality and follow-up mortality were secondary outcomes. To investigate the association between ROX index and mortality in AHRF patients, restricted cubic spline curve and COX proportional risk regression were utilized.

Result: A non-linear association (L-shaped) has been observed between the ROX index and mortality rate. When the ROX index is below 8.28, there is a notable decline in the 28-day mortality risk of patients as the ROX index increases (HR per SD, 0.858 [95%CI 0.794-0.928] P < 0.001). When the ROX index is above 8.28, no significant association was found between the ROX index and 28-day mortality. In contrast to the Q1 group, the mortality rates in the Q2, Q3, and Q4 groups had a substantial reduction (Q1 vs. Q2: HR, 0.749 [0.590-0.950] P = 0.017; Q3: HR, 0.711 [0.558-0.906] P = 0.006; Q4: HR, 0.641 [0.495-0.830] P < 0.001).

Conclusion: The ROX index serves as a valuable predictor of mortality risk in adult patients with AHRF, and that a lower ROX index is substantially associated with an increase in mortality.

Keywords: Acute hypoxemic respiratory failure; MIMIC-IV; Mortality; ROX index.

Fig. 1

Flowchart of patient selection

Fig. 2

Restricted cubic spline (RCS) curve of the ROX index and HR in patients with acute hypoxemic respiratory failure. (A) RCS curve for 28-day mortality. (B) RCS curve for 3-month mortality. (C) RCS curve for 6-month mortality. (D) RCS curve for 1-year mortality. (E) RCS curve for in-ICU mortality. (F) RCS curve for in-hospital mortality

Fig. 3

Forest plots of all-cause mortality in subgroups

Fig. 4

Kaplan–Meier survival analysis curves for all-cause mortality. ROX index: Q1 (ROX ≤ 5.89), Q2 (5.89 < ROX ≤ 8.28), Q3 (8.28 < ROX ≤ 11.24), Q4 (ROX > 11.24). Kaplan–Meier curves showing cumulative probability of all-cause mortality according to groups at 28 days (A), 3 months (B), 6 months (C) and 1 year (D)