The index of oxygenation to respiratory rate as a prognostic factor for mortality in Sepsis

An index combining respiratory rate and oxygenation (ROX) has been introduced, and the ROX index is defined as the ratio of oxygen saturation by pulse oximetry/fraction of inspired oxygen to respiratory rate. In sepsis, hypoxemia and tachypnea are commonly observed. We performed this study to investigate the association between the ROX index and 28-day mortality in patients with sepsis or septic shock.

This retrospective study included 2862 patients. The patients were divided into three groups according to the ROX index: Group I (ROX index >20), Group II (ROX index >10 and ≤ 20), and Group III (ROX index ≤10).

The median ROX index was significantly lower in the nonsurvivors than in the survivors (12.8 and 18.2, respectively) (p < 0.001). The 28-day mortality rates in Groups I, II and III were 14.5%, 21.3% and 34.4%, respectively (p < 0.001). In the multivariable Cox regression analysis, Group III had an approximately 40% higher risk of death than Group I during the 28-day period (hazard ratio = 1.41, 95% confidence interval 1.13-1.76). The area under the curve of the ROX index was significantly higher than that of the quick Sequential Organ Failure Assessment score (p < 0.001).

The ROX index was lower in nonsurvivors than in survivors, and a ROX index less than or equal to 10 was an independent prognostic factor for 28-day mortality in patients with sepsis or septic shock. Therefore, the ROX index could be used as a prognostic marker in sepsis.