Canterbury Respiratory Research Group
Christchurch, New Zealand
To the Editor:
In 1971, Szucs et al1reported a series of 50
nonconsecutive angiographically proven cases of pulmonary embolism
(PE), all of which with Pao2 < 80
mm Hg, ie, “hypoxemia.” They concluded that normoxemia
effectively excludes the diagnosis of PE. In succeeding issues of
CHEST, there quickly followed a dozen or more
well-documented exceptions to this rule. This was one of the first of
many such “failed tests” to exclude PE.2
In more recent years, further retrospective studies3–4 of
nonconsecutive patients have been cited emphasizing the limitations of
blood gas analysis in this context. One of the most commonly quoted
articles5 was based on the Prospective Investigation of
Pulmonary Embolism Diagnosis Study findings. Stein et al5–
concluded that blood gas levels are of insufficient discriminant value
to permit the exclusion of the diagnosis of PE in about 30% of
patients without prior cardiopulmonary disease. However from Paul
Stein’s book,6 containing unpublished background
material, we learn that only 132 of 330 patients (40%) with PE and no
prior cardiopulmonary disease actually had their blood gas levels
measured while breathing room air. Since this was a small series of
nonconsecutive patients, the calculation of sensitivity and specificity
To date, only three studies4,7–8 have prospectively
studied the incidence of normoxemia in patients with PE. Egermayer et
al7found objective evidence of PE in 5 of 39 patients
(13%). Prediletto et al8 observed normoxemia in 14 of 312
consecutive patients (4%) with angiographic evidence of PE. In another
recent study,4 only 5 of 49 consecutive patients (10%)
with high-probability ventilation/perfusion lung scan results and an
intermediate pretest probability had normoxemia.4
PE is a complex and often poorly defined disease, and it is doubtful
that any one test will ever completely rule in or rule out the
diagnosis. However, in my opinion, blood gas analysis is a useful part
of the workup, and it is clear that normoxemia greatly diminishes the
pretest probability of PE, and may exclude clinically important events.
Editor’s note: Dr. Egermayer died subsequent to receipt of this letter.
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