Association between SpO2/FiO2 Ratio and PaO2/FiO2 Ratio in Different Modes of Oxygen Supplementation

Sheetal Babu; Kundavaram Pp Abhilash; Subramani Kandasamy; Mahasampath Gowri

doi:10.5005/jp-journals-10071-23977

Association between SpO₂/FiO₂ Ratio and PaO₂/FiO₂ Ratio in Different Modes of Oxygen Supplementation

Indian J Crit Care Med. 2021 Sep;25(9):1001-1005. doi: 10.5005/jp-journals-10071-23977.

Authors

Sheetal Babu¹, Kundavaram Pp Abhilash², Subramani Kandasamy³, Mahasampath Gowri⁴

Affiliations

¹ Surgical Intensive Care Unit, Christian Medical College, Vellore, Tamil Nadu, India.
² Emergency Department, Christian Medical College, Vellore, Tamil Nadu, India.
³ Division of Critical Care and Surgical ICU, Christian Medical College, Vellore, Tamil Nadu, India.
⁴ Department of Biostatistics, Christian Medical College, Vellore, Tamil Nadu, India.

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.

How to cite this article: Babu S, Abhilash KPP, Kandasamy S, Gowri M. Association between SpO₂/FiO₂ Ratio and PaO₂/FiO₂ Ratio in Different Modes of Oxygen Supplementation. Indian J Crit Care Med 2021;25(9):1001-1005.

Keywords: Acute hypoxemic respiratory failure (AHRF); Acute respiratory distress syndrome (ARDS); Arterial blood gas (ABG); Oxygen supplementation; PaO2/FiO2 ratio; Pulse oximetry; SaO2/FiO2 ratio.