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PaO2/FiO2 Ratio Formula:
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The PaO2/FiO2 ratio is a measure used in critical care medicine to assess the efficiency of oxygen exchange in the lungs. It's calculated by dividing the partial pressure of arterial oxygen (PaO2) by the fraction of inspired oxygen (FiO2).
The calculator uses the PaO2/FiO2 ratio formula:
Where:
Explanation: This simple ratio provides a quick assessment of pulmonary gas exchange function, with lower values indicating more severe impairment.
Details: The PaO2/FiO2 ratio is crucial for diagnosing and classifying acute respiratory distress syndrome (ARDS), monitoring respiratory status, and guiding oxygen therapy in critically ill patients.
Tips: Enter PaO2 in mmHg and FiO2 as a decimal value (e.g., 0.21 for room air, 0.4 for 40% oxygen). Both values must be valid (PaO2 > 0, FiO2 between 0.21-1.0).
Q1: What is a normal PaO2/FiO2 ratio?
A: A normal ratio is typically greater than 400 mmHg. Values between 300-400 indicate mild impairment, 200-300 moderate impairment, and below 200 severe impairment.
Q2: How is this ratio used in ARDS diagnosis?
A: The ratio is a key criterion for ARDS diagnosis: mild ARDS (200-300), moderate ARDS (100-200), and severe ARDS (<100) when measured with PEEP ≥5 cm H2O.
Q3: When should this calculation be performed?
A: This calculation is particularly useful in critical care settings for patients receiving supplemental oxygen, especially when assessing for possible ARDS.
Q4: Are there limitations to this ratio?
A: The ratio doesn't account for variables like PEEP levels, mean airway pressure, or patient position. It's also less accurate at very high FiO2 levels.
Q5: How does this differ from the oxygenation index?
A: The oxygenation index (OI) incorporates mean airway pressure: OI = (FiO2 × MAP × 100)/PaO2, providing a more comprehensive assessment of oxygenation efficiency.