Background: A study done in Philippine Heart Center conducted by Malicdem et al, concluded that SPO/ Fi02 (S/F) ratio can be a substitute for PaO/Fi02 (P/F) ratio in the diagnosis of Acute Lung Injury (All) and Acute Respiratory Disease Syndrome (ARDS) in adults. However, the critical threshold value for S/F ratio is not determined. The focus of this research paper is to determine the critical threshold value of S/F ratio in the diagnosis of All particularly among critically ill Filipino patients.
Method: This is an analytical, cross-sectional study conducted in Philippine Heart Center from June 2008 to December 2011. All admitted patients diagnosed to have ALl/ARDS were included in this study. All patients had measured 02 sat and Pa02 with documentation of inhaled concentration of oxygen at the study enrollment. SP02 values were documented at the time of ABG sampling. The following measures was observed to improve the accuracy of the SP02: optimal position and cleaning of the sensor; satisfactory waveforms; no position changes or endobronchial suctioning for at least 10 minutes prior to the measurement and no invasive procedures or ventilator manipulation for at least 30 minutes prior to the measurement. Sp02 were observed for a minimum of one minute before the value is recorded. SpO/Fi02 was then computed and was compared with PaO/Fi02 ratio. We determined the best cut off value for S/F ratio as well as the sensitivity, specificity, and likelihood ratio.
Results: The determination of the critical threshold of S/F ratio for ALl/ARDS was conducted and evaluated. Corresponding measurements of PF and SF ratio was obtained from 106 intubated patients with the diagnosis of Respiratory Failure Type I, non-cardiogenic (All). A Linear Regression Model [S/F = 29.6 + 1.09 (P/F); p < 0.000] was obtained to determine the critical threshold of the SF ratio. A correlation coefficient of 0.804 was obtained between the P/F and S/F ratio which yielded the critical threshold for SF ratio of 248 for PF ratio s 200 and a critical threshold SF ratio of 357 for PF ratio s 300. Analysis between ROC AUC of 0.645 and the inverse of Fi02 correlates with PF ratio (r=0.604) indicate a consistent agreement between that S/F and P/F ratios. The SF ratio threshold of 248 (corresponding to P/F s 200) yielded a sensitivity of 100% and specificity value of 96.23% with a likelihood ratio of 26.5 (95% Cl: 6.80 - 103.20) for ARDS, while S/F ratio threshold of 357 (corresponding to P/F; 300) had a sensitivity and specificity of 100% and 98.19%, respectively with likelihood ratio of 66.23 (95% Cl: 18.7 - 283.8) for ALI.
Conclusion: The high correlation between the S/F and P/F ratio as well as the consistent relationships between ROC AUC and inverse Fi02 vs. PF ratio, excellent sensitivity and very satisfactory specificity for ARDS and All indicate that the threshold S/F ratio of 248 and 357 for P/F ratio of 200 and 300 can measure and discriminate ARDS and All among critically ill Filipino patients.