PaO2/FiO2 Ratio – #FOAMed (2024)

FAQs

What is the PaO2 FiO2 ratio? ›

How to Calculate the P/F Ratio: PaO2 / FIO2. “P” represents PaO₂ (arterial pO2) from the ABG. “F” represents the FIO₂ – the fraction (percent) of inspired oxygen that the patient is receiving expressed as a decimal (40% oxygen = FIO₂ of 0.40). P divided by F = P/F ratio.

PaO2 should = FiO2 x 500 (e.g. 0.21 x 500 = 105 mmHg)

Dependent upon PaO2 response, patients were reclassified into three groups: mild (PaO2/FiO2 > 200), moderate (PaO2/FiO2 101-200), and severe (PaO2/FiO2 ≤ 100) ARDS.

The arterial oxygen pressure (PaO2) can be directly assessed with an arterial blood gas test (ABG) or estimated with a venous blood gas test (VBG). The alveolar oxygen pressure (PAO2) is not easily measured directly; instead, it is estimated using the alveolar gas equation: PAO2 = (Patm – PH2O) FiO2 – PaCO2/RQ.

12. What is considered normal for the PaO2/FiO2 ratio? A normal PaO2/FiO2 ratio while breathing room air is approximately 400 to 500 mm Hg.

PaO2 is one of the indicators of tissue oxygenation. The ratio between PaO2 and FiO2 {PaO2, FiO2} is the most common index to evaluate oxygenation. PaO2, FiO2 ratio Less than 300 is indicative of Acute Lung Injury {ALI} and Less than 200 of Acute Respiratory Distress Syndrome {ARDS}.

The distinguishing characteristic of Type 1 respiratory failure is a partial pressure of oxygen (PaO2) < 60 mmHg with a normal or decreased partial pressure of carbon dioxide (PaCO2). Depending on the cause of hypoxemia, the alveolar-arterial (A-a) gradient may be normal or increased.

Natural air includes 21% oxygen, which is equivalent to F_IO₂ of 0.21. Oxygen-enriched air has a higher F_IO₂ than 0.21; up to 1.00 which means 100% oxygen. F_IO₂ is typically maintained below 0.5 even with mechanical ventilation, to avoid oxygen toxicity, but there are applications when up to 100% is routinely used.

Normal Results

Partial pressure of oxygen (PaO2): 75 to 100 millimeters of mercury (mm Hg), or 10.5 to 13.5 kilopascal (kPa) Partial pressure of carbon dioxide (PaCO2): 38 to 42 mm Hg (5.1 to 5.6 kPa) Arterial blood pH: 7.38 to 7.42. Oxygen saturation (SaO2): 94% to 100%

An acceptable normal range of ABG values of ABG components is the following,[27][28] noting that the range of normal values may vary among laboratories and in different age groups from neonates to geriatrics: pH (7.35-7.45) PaO₂ (75-100 mm Hg) PaCO₂ (35-45 mm Hg)

What is the ratio for ARDS? ›

The diagnosis of ARDS is based on the following criteria: acute onset, bilateral lung infiltrates on chest radiography or CT scan (who are of non-cardiac origin), and a PaO₂/FiO₂ ratio of less than 300 mm Hg.

A PaO2 test measures partial pressure of oxygen, or PaO2—the oxygen pressure in arterial blood. The PaO2 reflects how well oxygen is able to move from the lungs to the blood. It is often altered by severe illnesses, with the PaO2 test results used to guide treatment.

To calculate the PaO₂/FiO₂ ratio, the PaO₂ is measured in mmHg and the FiO₂ is expressed as a decimal between 0.21 and 1. As an example, if a patient has a PaO₂ of 100 mmHg while receiving 80 percent oxygen, then the PaO₂/FiO₂ ratio is 125 mm Hg (e.g., 100 mm Hg/0.8).

Conclusion: SF ratio is a reliable noninvasive surrogate for PF ratio to identify children with ALI or ARDS with the advantage of replacing invasive arterial blood sampling by non-invasive pulse oximetry.

Normal Results

Partial pressure of oxygen (PaO2): 75 to 100 millimeters of mercury (mm Hg), or 10.5 to 13.5 kilopascal (kPa) Partial pressure of carbon dioxide (PaCO2): 38 to 42 mm Hg (5.1 to 5.6 kPa) Arterial blood pH: 7.38 to 7.42. Oxygen saturation (SaO2): 94% to 100%

Natural air includes 21% oxygen, which is equivalent to F_IO₂ of 0.21. Oxygen-enriched air has a higher F_IO₂ than 0.21; up to 1.00 which means 100% oxygen. F_IO₂ is typically maintained below 0.5 even with mechanical ventilation, to avoid oxygen toxicity, but there are applications when up to 100% is routinely used.