Capnometry in suspected pulmonary embolism with positive D-dimer in the field

Pulmonary embolism (PE) is one of the greatest diagnostic challenges in prehospital emergency setting. Most patients with suspected PE have a positive D-dimer and undergo diagnostic testing. Excluding PE with additional non-invasive tests would reduce the need for further imaging tests. We aimed to determine the effectiveness of combination of clinical probability and end-tidal carbon dioxide (PetCO2) for evaluation of suspected PE with abnormal concentrations of D-dimer in prehospital emergency setting. We assessed clinical probability of PE and PetCO2 measurement in 100 consecutive patients with suspected PE and positive D-dimer in the field. PetCO2 > 28 mmHg was considered as the best cut-off point. PE was excluded or confirmed by hospital physicians in the University Clinical Center Maribor by computer tomography (CT), ventilation/perfusion scan echocardiography and pulmonary angiography. PE was confirmed in 41 patients. PetCO2 had a sensitivity of 92.6% (95% CI, 79 to 98%), a negative predictive value of 94.2% (95% CI, 83 to 99%), a specificity of 83% (95% CI, 71 to 91%) and a positive predictive value of 79.2% (95% CI, 65 to 89%). Thirty-five patients (35%) had both a low (PE unlikely) clinical probability and a normal PetCO2 (sensitivity: 100%, 95% CI: 89 to 100%) and twenty-eight patients (28%) had both a high clinical probability (PE likely) and abnormal PetCO2 (specificity: 93.2%, 95% CI: 83 to 98%). The combination of clinical probability and PetCO2 may safely rule out PE in patients with suspected PE and positive D-dimer in the prehospital setting.