Retrospective validation of a new volumetric capnography parameter for the exclusion of pulmonary embolism at the emergency department.

Volumetric capnography might be used to exclude pulmonary embolism (PE) without the need for computed tomography pulmonary angiography. In a pilot study, a new parameter (CapNoPE) combining the amount of carbon dioxide exhaled per breath (carbon dioxide production (V CO2 )), the slope of phase 3 of the volumetric capnogram (slope 3) and respiratory rate (RR) showed promising diagnostic accuracy (where CapNoPE=(V CO2 ×slope 3)/RR). To retrospectively validate CapNoPE for the exclusion of PE, the volumetric capnograms of 205 subjects (68 with PE) were analysed, based on a large multicentre dataset of volumetric capnograms from subjects with suspected PE at the emergency department. The area under the curve (AUC) of the receiver operating characteristic (ROC) curve and diagnostic accuracy of the in-pilot established threshold (1.90 Pa·min) were calculated. CapNoPE was 1.56±0.97 Pa·min in subjects with PE versus 2.51±1.67 Pa·min in those without PE (p<0.001). The AUC of the ROC curve was 0.714 (95% CI 0.64-0.79). For the cut-off of ≥1.90 Pa·min, sensitivity was 64.7%, specificity was 59.9%, the negative predictive value was 77.4% and the positive predictive value was 44.4%. The CapNoPE parameter is decreased in patients with PE but its diagnostic accuracy seems too low to use in clinical practice.