Association between SpO2/FiO2 Ratio and PaO2/FiO2 Ratio in Different Modes of Oxygen Supplementation
Mahasampath Gowri, Sheetal Babu
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 SpO 2 /FiO 2 (SF) ratio can be used as a surrogate to invasive index PaO 2 /FiO 2 (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 crosssectional study. Fraction of inspired oxygen (FiO 2 ), method of oxygen supplementation, and partial pressure of arterial oxygen (PaO 2 ) were noted from the ABG reports in the medical records. The corresponding SpO 2 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.