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Listen to PaO2/FiO2 ratios: they tell us about length of stay

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Classification of respiratory distress has been dependent on PaO2/FiO2; that is, <300 acute lung injury (ALI) and <200 acute respiratory distress syndrome (ARDS). In this study, PaO2/FiO2 was analyzed for predicting ICU patients' length of stay (LOS).


Data of 273 patients admitted to the ICU with RI were retrospectively analyzed for LOS in the ICU. Patients admitted to the emergency department (ED) with RI, documented arterial blood gas analysis (ABGA), and hospitalized in the ICU were eligible for this study within 4 years. The first ABGA in ED PaO2/FiO2 were taken for predicting ICU LOS. Patients' comorbid diseases, APACHE II/Glasgow scores, non/invasive mechanical ventilation supports were not included in the analysis. Patients were classified into three groups as: (1) >300 not having RI, (2) <300 ALI, (3) <200 ARDS; they were then compared for predicting ICU LOS, and also receiver operating curve (ROC) analysis and area under curve (AUC) were calculated.


Analysis showed statistical significance of P < 0.01 for all groups pointing out that ED ABGA PaO2/FiO2 levels negatively affected patients' LOS in the ICU. ROC analysis of PaO2/FiO2 for LOS showed significant AUC: 0.917 levels, which was predicted as a powerful indicator. Patients' data are presented in Table 1.

Table 1 Patient data


We concluded that the PaO2/FiO2 ratio was a powerful indicator for predicting ICU LOS in patients with RI. In addition there was no need to classify patients according to PaO2/FiO2 to predict LOS; any decreased ratio meant a longer LOS. However, this study was weak in power; it had a small sample, did not include comorbid conditions, did not account for accepted scoring systems, and did not include daily ABGA for prediction. On the other hand, these results are promising for future observations that ABGA taken in the ED would be a supplemental tool for the physician's approach in the ICU.

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Correspondence to V Inal.

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Inal, V., Comert, B. & Yamanel, L. Listen to PaO2/FiO2 ratios: they tell us about length of stay. Crit Care 16, P89 (2012).

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  • Public Health
  • Emergency Department
  • Mechanical Ventilation
  • Emergency Medicine
  • Comorbid Condition