Association between spo2/fio2 ratio and pao2/fio2 ratio in different modes of oxygen supplementation

Abstract

Background: Acute hypoxemic respiratory failure (AHRF) is a major factor for increased mortality in the intensive care unit (ICU). We hypothesized that the noninvasive index SpO2/FiO2 (SF) ratio can be used as a surrogate to invasive index PaO2/FiO2 (PF) as SF ratio correlates with PF ratio in all modes of oxygen supplementation. Patients and methods: Patients with acute respiratory failure admitted to the intensive care unit were enrolled in this retrospective cross-sectional study. Fraction of inspired oxygen (FiO2), method of oxygen supplementation, and partial pressure of arterial oxygen (PaO2) were noted from the ABG reports in the medical records. The corresponding SpO2 was noted from the nurse’s chart. The calculated SF and PF ratios were recorded, and correlation between the same was noted in different methods of oxygen administration. Results: A total of 300 sample data were collected. Pearson’s correlation was used to quantify the relationship between the variables. The study showed a positive correlation, r = 0.66 (p <0.001), between PF ratio and SF ratio. SF threshold values were 285 and 323 for corresponding PF values of 200 and 300 with a sensitivity and specificity in the range of 70 to 80%. In addition, SF and PF could also be used interchangeably irrespective of the mode of oxygen supplementation, as the median values of PF ratio (p = 0.06) and SF ratio (p = 0.88) were not statistically significant. Conclusion: In patients with AHRF, the noninvasive SF ratio can be used as a surrogate to invasive index PF in all modes of oxygen supplementation.