Q&A: Querying for acute respiratory failure

Q: If a patient is extubated post-operatively but continues to be treated with supplemental oxygen, when is a query for acute respiratory failure appropriate?

A: To determine if this represents acute respiratory failure, the values for impaired oxygen exchange can be used, along with the amount of oxygen being administered to the patient.

The ratio of arterial oxygen concentration to the fraction of inspired oxygen (P/F ratio) can be a helpful tool to identify respiratory failure criteria above for a patient receiving supplemental oxygen:

• The P/F ratio is an indicator of hypoxemia. This is a useful tool when a patient is on supplemental oxygen.
• The P/F ratio is provided on arterial blood gas (ABG) tests.
• A P/F ratio less than 300 suggests acute respiratory failure.

If an ABG test is not available, an estimated P/F ratio can be calculated:

• The calculation is pO2 divided by FIO2:
  
  • The FIO2 is determined by the liters of oxygen the patient is receiving expressed as a decimal (e.g., 32% is .32).

An illustration of the calculation shows that if a patient is receiving 3L oxygen by nasal cannula, and has a pO2 of 40 mm Hg. That would be 40/.32, which results in 125 (acute respiratory failure). The P/F ratio is a useful tool to validate the presence of acute hypoxemic respiratory failure when patients are receiving supplemental oxygen. After following this formula, and acute respiratory failure is still in question, then a query to your physician is needed.

Editor’s note: This article was originally published in JustCoding. This question was answered by Robert Stein, MD, CCDS, associate director of the MS-DRG Assurance program for Enjoin. Join him for a webinar on this topic on March 21!