How effective is PaO2 level on ABG analysis in predicting pulmonary embolism (PE)?

Updated: Jun 06, 2019
  • Author: Daniel R Ouellette, MD, FCCP; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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Answer

In most settings, fewer than half of all patients with symptoms suggestive of pulmonary embolism actually turn out to have pulmonary embolism as their diagnosis. In such a population, if any reasonable level of PaO2 is chosen as a dividing line, the incidence of pulmonary embolism will be higher in the group with a PaO2 above the dividing line than in the group whose PaO2 is below the divider. This is a specific example of a general truth that may be demonstrated mathematically for any test finding with a Gaussian distribution and a population incidence of less than 50%.

Conversely, in a patient population with a very high incidence of pulmonary embolism and a lower incidence of other respiratory ailments (eg, postoperative orthopedic patients with sudden onset of shortness of breath), a low PO2 has a strongly positive predictive value for pulmonary embolism.

The discussion above holds true not only for arterial PO2 but also for the alveolar-arterial oxygen gradient and for the oxygen saturation level as measured by pulse oximetry. In particular, pulse oximetry is extremely insensitive, is normal in the majority of patients with pulmonary embolism, and should not be used to direct a diagnostic workup.


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