Evaluation of suspected pulmonary embolism utilizing end-tidal CO2 and D-dimer

Background: The study prospectively assesses deadspace [(arterial CO2 − end-tidal CO2)/arterial CO2] and the D-dimer assay as a rapid, noninvasive alternative for evaluating pulmonary embolism in critically ill patients. Methods: Group I patients had nonemergency baseline arterial blood gas and end-tidal CO2 recorded. If patients experienced respiratory distress, D-dimer with repeat arterial blood gas and end-tidal CO2 were obtained. Patients emergently intubated without baseline laboratory studies (group II) had arterial blood gas, end-tidal CO2, and D-dimer obtained. Results: A significant increase (P <0.001) in deadspace was noted with pulmonary embolism (0.43 [0.08], range 0.30 to 0.51, n = 7) versus without (0.21 [0.15], range 0.00 to 0.43, n = 14). Patients in group 1 with pulmonary embolism demonstrated increased deadspace (P <0.026, 0.28 [0.01] to 0.39 [0.13], n = 2) from baseline compared with decreased deadspace (P <0.001, 0.20 [0.09] to 15 [0.16], n = 9) without pulmonary embolism. D-dimer levels >1,000 ng/mL were present in all patients with pulmonary embolism. Conclusions: The study demonstrates the ability of deadspace and D-dimer to exclude and potentially diagnose pulmonary embolism.