Recognizing acute respiratory failure

Acute respiratory failure is a very important and surprisingly common diagnosis, especially among patients who are admitted with heart failure, pneumonia or chronic obstructive pulmonary disease (COPD). The clinical definition applies to any patient who has difficulty breathing and either of the following:

  • Type I: Hypoxemic, pO2 <60 mm Hg while breathing room air
  • Type II: Hypercapnic, pCO2 >50 mm Hg, usually with pH <7.35
Photo by Comstock
Photo by Comstock.

The words “acute respiratory failure” must be used to describe these patients because other commonly used clinical terminology—such as hypoxia, respiratory distress, dyspnea, respiratory or pulmonary insufficiency—does not result in the assignment of the correct code for acute respiratory failure. Note that respiratory problems following surgery or trauma (which will be the subject of a future column) are dealt with in an entirely different way by official coding rules.

Pulse oximetry (SpO2) can be used to measure hypoxemia. A reading of 88% or less directly correlates with a pO2 that is definitely less than 60 mm Hg, indicating that acute respiratory failure is present. If a room-air reading is not available, physicians should use their clinical judgment to determine whether acute respiratory failure is present by estimating whether the SpO2 would likely fall below 88% (or the pO2 below 60 mm Hg) if oxygen were discontinued.

An exception to the hypoxemic criteria above would be a patient with severe COPD and chronic respiratory failure whose baseline pO2 is less than 60 mm Hg (SpO2 ≤88%). In this situation, a pO2 that is 10 mm Hg below baseline is proof of acute respiratory failure. Many of these patients also have a pCO2 elevated above 50 mm Hg (which, as noted above, is the cutoff for hypercapnic respiratory failure), so any degree of acidosis (pH <7.35) indicates that acute respiratory failure (e.g. “acute on chronic respiratory failure”) is also present.

Does the patient have to be on a ventilator?

Not all patients with acute respiratory failure require intubation and mechanical ventilation; many can be managed with non-invasive techniques such as BiPAP and other aggressive respiratory modalities.

On the other hand, when intubation and ventilation are required, it is extremely important to document acute respiratory failure, except in the unusual situation when ventilation is needed for another reason. This is especially significant when a patient is admitted following resuscitation from cardiopulmonary arrest, to explain the medical necessity of mechanical ventilation.

Early documentation is essential. Even if respiratory failure resolves quickly, it is still very likely to qualify as the principal reason for admission, or it will be a very important comorbid condition that contributes substantially to the patient's severity of illness and complexity of care. The admitting physician should review the emergency department record for evidence that the patient meets the acute respiratory failure criteria and document it.

In summary, always consider acute respiratory failure in patients admitted with COPD, heart failure, pneumonia, asthma, and other respiratory or neuromuscular disorders; then document it in the medical record if present. Also remember to include the diagnosis of acute respiratory failure when a patient requires intubation.