Is Bedside End-Tidal CO₂ Measurement a Screening Tool to Exclude Pulmonary Embolism in Emergency Department?

Pulmonary embolism (PE) is among the most difficult conditions to diagnose in emergency department. The majority of patients thought to have PE are tested positive for D-dimer and subsequently tested with advanced diagnostic modalities. Novel noninvasive tests capable of excluding PE may obviate the need for advanced imaging tests. We studied the role of combined clinical probability assessment and end-tidal carbon dioxide (ETCO₂) measurement for diagnosis of possible PE in emergency department.

We included 100 consecutive subjects suspected to have PE and a positive D-dimer test to study clinical probability of PE and ETCO₂ levels. ETCO₂ > 34 mm Hg was found to be the best cut-off point for diagnosing PE. PE was ultimately eliminated or diagnosed by spiral computed tomography (CT).

Diagnostic performances of tests were as follows: ETCO₂ and D-dimer had a sensitivity of 100% and a negative predictive value (NPV) of 100% at the cut-off levels of 34 mm Hg and 500 ng/mL, respectively; Wells score had a sensitivity of 80% and NPV of 69.7% at a score of 4.

ETCO₂ alone cannot reliably exclude PE. Combining it with clinical probability, however, reliably and correctly eliminates or diagnoses PE and prevents further testing to be done.