Clinical Characteristics and Outcomes Are Similar in ARDS Diagnosed by Oxygen Saturation/Fio2 Ratio Compared With Pao2/Fio2 Ratio.
BACKGROUND
Oxygen saturation as measured by pulse oximetry/Fio2 (SF) ratio is highly correlated with the Pao2/Fio2 (PF) ratio in patients with ARDS. However, it remains uncertain whether SF ratio can be substituted for PF ratio for diagnosis of ARDS and whether SF ratio might identify patients who are systemically different from patients diagnosed by PF ratio.


METHODS
We conducted a secondary analysis of a large observational prospective cohort study. Patients were eligible if they were admitted to the medical ICU and fulfilled the Berlin definition of ARDS with hypoxemia criteria using either the standard PF threshold (PF ratio ≤ 300) or a previously published SF threshold (SF ratio ≤ 315).


RESULTS
Of 362 patients with ARDS, 238 (66%) received a diagnosis by PF ratio and 124 (34%) by SF ratio. In a small group of patients who received diagnoses of ARDS by SF ratio who had arterial blood gas measurements on the same day (n = 10), the PF ratio did not meet ARDS criteria. There were no major differences in clinical characteristics or comorbidities between groups with the exception of APACHE (Acute Physiology and Chronic Health Evaluation) II scores, which were higher in the group diagnosed by PF ratio. However, this difference was no longer apparent when arterial blood gas-dependent variables (pH, Pao2) were removed from the APACHE II score. There were also no differences in clinical outcomes including duration of mechanical ventilation (mean, 7 days in both groups; P = .25), duration of ICU stay (mean, 10 days vs 9 days in PF ratio vs SF ratio; P = .26), or hospital mortality (36% in both groups, P = .9).


CONCLUSIONS
Patients with ARDS diagnosed by SF ratio have very similar clinical characteristics and outcomes compared with patients diagnosed by PF ratio. These findings suggest that SF ratio could be considered as a diagnostic tool for early enrollment into clinical trials.
Division of Allergy, Pulmonary, and Critical Care Medicine, Louisiana State University School of Medicine, New Orleans, LA; Vanderbilt University School of Medicine, Nashville, TN; the Division of Pulmonary and Critical Care Medicine, Louisiana State University School of Medicine, New Orleans, LA; Chiayi Christian Hospital, Chiayi, Taiwan; the Department of Life Science, Louisiana State University School of Medicine, New Orleans, LA; National Chung Hsing University, Taichung, Taiwan; the College of Nursing, Louisiana State University School of Medicine, New Orleans, LA. Electronic address: peteralfa2004@yahoo.com.tw.
Wei
W
Chen
Da-Yeh University, Taichung, Taiwan; and the Section of Pulmonary and Critical Care Medicine, Louisiana State University School of Medicine, New Orleans, LA.
David R
DR
Janz
Division of Allergy, Pulmonary, and Critical Care Medicine, Louisiana State University School of Medicine, New Orleans, LA.
Ciara M
CM
Shaver
Division of Allergy, Pulmonary, and Critical Care Medicine, Louisiana State University School of Medicine, New Orleans, LA.
Gordon R
GR
Bernard
Division of Allergy, Pulmonary, and Critical Care Medicine, Louisiana State University School of Medicine, New Orleans, LA.
Julie A
JA
Bastarache
Division of Allergy, Pulmonary, and Critical Care Medicine, Louisiana State University School of Medicine, New Orleans, LA.
Lorraine B
LB
Ware
D018806:APACHE; D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis / Q000379:methods*; D015331:Cohort Studies; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D000860:Hypoxia / Q000175:diagnosis / Q000209:etiology; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D011446:Prospective Studies; D012128:Respiratory Distress Syndrome / Q000097:blood / Q000150:complications / Q000175:diagnosis
D010100:Oxygen