PaCO₂-EtCO₂ Gradient and D-dimer in the Diagnosis of Suspected Pulmonary Embolism

The diagnosis of pulmonary embolism (PE) because of nonspecific clinical presentation remains as a challenge for emergency physicians. Arterial to end-tidal partial pressure of carbon dioxide (P(a-Et) CO₂) gradient may be useful in the evaluation of PE. This aimed to define the diagnostic role of P(a-Et)CO₂ gradient by sidestream capnography, as a noninvasive method, and D-dimer in patients with PE.

Two hundred and three patients with chest pain or dyspnea who attend the hospital emergency ward were enrolled over a study period at a single academic center. PE was confirmed by multidetector computed tomography (MDCT) scans. PaCO₂, EtCO₂, and D-dimer were measured within 24 h of MDCT by capnograph.

The combination of P(a-Et)CO₂ gradient (cutoff >9.2 ng/ml) and D-dimer (cutoff >3011 ng/ml) with sensitivity and specificity of 30.2% and 87.2% showed a significant diagnostic value in detecting PE (area under the curve = 0.577, P = 0.045) but not alone (P > 0.05).

As the results show, the combination of P(a-Et)CO₂ gradient and D-dimer can show an acceptable diagnostic value in detecting PE, although it suggests further research on evaluating the diagnostic value of P(a-Et)CO₂ gradient and combining it with other diagnostic criteria to achieve a definite and generalizable result.