P/F Ratio Calculator
Calculate your About P/F Ratio.
Calculate your About P/F Ratio.
The P/F ratio is an easy way to gauge how severe hypoxemia is. It is the ratio of arterial blood gas's FiO2 to arterial blood gas' PaO2 (arterial oxygen partial pressure) (fraction of inspired oxygen expressed as a decimal). The P/F ratio, for instance, is 475 for a person breathing room air (21% oxygen, or a FiO2 of 0.21), with a PaO2 of 100 mmHg. P/F is also used to stratify the severity of acute respiratory distress syndrome (ARDS) in accordance with the Berlin criteria and in various scoring systems, such as the APACHE-IV.
The P/F ratio is used to assess the severity of hypoxemia. It is the ratio of the PaO2 (partial pressure of oxygen) to the FiO2 (fraction of inspired oxygen) and is expressed as:
P/F Ratio = PaO2 / FiO2
For example, a PaO2 of 83 mmHg and FiO2 of 0.45 would give a P/F ratio of 83 / 0.45 = 184. Anything below 300 is indicative of ARDS (acute respiratory distress syndrome).
The formula for calculating the P/F ratio is:
P/F Ratio = PaO2 / FiO2
Where PaO2 is the arterial oxygen partial pressure from the ABG (arterial blood gas), and FiO2 is the fraction of inspired oxygen, typically represented as a decimal (e.g., 40% oxygen = FiO2 of 0.40).
Hypoxemia is defined as a subnormal concentration of oxygen in the blood, while hypoxia refers to tissues with insufficient oxygen levels. While hypoxemia is a blood gas condition, hypoxia describes the oxygenation of tissues.
A V/Q mismatch occurs when a portion of your lung gets oxygen without blood flow, or blood flow without oxygen. This can happen due to conditions like a pulmonary embolism, choking, or medical conditions affecting breathing. A V/Q ratio outside the normal value (0.8) can lead to hypoxemia and respiratory failure.
PaO2 (partial pressure of oxygen) measures the actual oxygen concentration in arterial blood, whereas SpO2 (oxygen saturation) refers to the percentage of hemoglobin molecules in the blood that are carrying oxygen. PaO2 is measured via blood gas tests, while SpO2 is measured using a pulse oximeter.