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

Introduction 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 noninvasive 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 (PetCO(2)) for evaluation of suspected PE with abnormal concentrations of D-dimer in prehospital emergency setting. Methods We assessed clinical probability of PE and PetCO(2) measurement in 100 consecutive patients with suspected PE and positive D-dimer in the field. PetCO(2) > 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. Results PE was confirmed in 41 patients. PetCO(2) 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 PetCO(2) (sensitivity: 100%, 95% CI: 89 to 100%) and twenty-eight patients (28%) had both a high clinical probability (PE likely) and abnormal PetCO(2) (specificity: 93.2%, 95% CI: 83 to 98%). Conclusions The combination of clinical probability and PetCO(2) may safely rule out PE in patients with suspected PE and positive D-dimer in the prehospital setting.