Can pulse oximetric saturation (SpO2)/fraction of inspired oxygen (FiO2) ratio surrogate PaO2/ FiO2 ratio in diagnosing acute respiratory failure?

Abstract

Introduction: The condition of acute respiratory failure is one of the most common as well as serious condition that is encountered in the ICU. Diagnosis and immediate management can increase the rate of survival among these patients. Aiming to attain this goal and to ensure that no invasive procedure is tried on the patient several studies have tried to substitute the use of PaO 2 /FiO 2 which is an invasive procedure and risky for patients who have severe blood loss or are anaemic by other reliable markers out of which SpO 2 /FiO 2 has shown some promise in paediatric age groups. Another disadvantage of using PaO 2 /FiO 2 is the time it takes to evaluate the condition and give us results that can help us diagnose the patient .This study explores the possibility of it being used for the adult age group. Materials and methods: A sample size of 50 patients was taken and a total of 101 observations from these patients were recorded. The observations from these patients included SpO 2 /FiO 2 , PaO 2 /FiO 2 , vitals (heart rate, respiratory rate, SBC, blood pressure), presence of crepitations, chest X ray infiltrates and the use of ventilator. A statistical analysis was then undertaken comparing SpO 2 /FiO 2 ratio and PaO 2 /FiO 2 ratio. This correlation was statistically analysed by plotting graphs and was checked whether they are significant or insignificant. Result: It was observed that SpO 2 /FiO 2 ratio correlates very well with PaO 2 /FiO 2 ratio (R = 0.375). A formula was also derived using the graph which could help us find value of SpO 2 /FiO 2 ratio using PaO 2 /FiO 2 ratio and vice versa. SpO 2 /FiO 2 =0.559(PaO 2 /FiO 2 )+157.9 Conclusion: From the above study we can conclude that PaO 2 /FiO 2 can be surrogated by the use of SpO 2 /FiO 2 ratio which is much more inexpensive, invasive and most of all saves the time required for doing ABG analysis in adult age group also.