Volumetric or time‐based capnography for excluding pulmonary embolism in outpatients?

Abstract

Summary. Background: Volumetric capnography is technically more demanding but theoretically better than the time-based alveolar deadspace fraction (P a CO 2 -EtCO 2 )/P a CO 2 as a bedside diagnostic tool for excluding pulmonary embolism (PE) in outpatients. Objective: We compared both diagnostic accuracy in patients with a suspected PE and positive D-dimer enzymelinked immunosorbent assay results. Patients and methods: In this clinical multicenter trial with prospective inclusion and 3-month follow-up, alveolar deadspace fraction was compared by receiver operating characteristic (ROC) analysis with other parameters derived from volumetric capnography. Results: Capnography was performed in 239 patients, and 205 tests (86%) were conclusive. The incidence of PE was 33%. The alveolar deadspace fraction accuracy expressed with ROC curve analysis was 0.73 ± 0.04. The diagnostic performances of parameters from volumetric capnography were not significantly better. Sixteen per cent [95% confidence interval (CI) 12-21%] of patients presented a (P a CO 2 -EtCO 2 )/P a CO 2 ratio under the cut-off value of 0.15, with a low clinical probability. This combination excluded PE, with a sensitivity of 96% (95% CI 89-99%) and a negative likelihood ratio of 0.17 (95% CI 0.09-0.33%). Conclusion: Volumetric capnography failed to show superiority to alveolar deadspace fraction measurements [(P a CO 2 -EtCO 2 )/P a CO 2 ] for exclusion of PE in outpatients with positive D-dimer test results. Future studies should clarify the safety of excluding PE in patients combining low clinical probability with positive D-dimer results and (P a CO 2 -EtCO 2 )/P a CO 2 ratios below the cut-off value of 0.15.

Pathophysiology of dyspnoea in acute pulmonary embolism: A cross‐sectional evaluation

“…The following ventilatory parameters were automatically analysed: tidal volume (VT), inspiratory time (Ti), total duration of respiratory cycle (Ttot), their coefficients of variation (CV) and FECO 2 (end‐tidal CO 2 and its CV). Patients stabilized their breathing patterns and the CV of FECO 2 was used as an index of stabilization . This stabilization period lasted from 60 to 90 s, and then the parameters were recorded for two additional minutes.…”

“…This stabilization period lasted from 60 to 90 s, and then the parameters were recorded for two additional minutes. The steady‐state alveolar dead space fraction was calculated using Bohr's equation, as previously reported . We previously validated the accuracy of transcutaneous PCO 2 measurement …”

Splendors and miseries of expired CO2 measurement in the suspicion of pulmonary embolism

“…First, technical improvements now allow measuring CO 2 not only for monitoring purposes in intubated patients in operating rooms but also as a diagnostic tool in spontaneously breathing patients in the emergency department or even in the field. Second, volumetric capnography, which displays expired CO 2 as a function of the expired volume of the patient, did much to renew interest in capnography because of its potential for better performance in diagnosing PE than the arterial to endtidal CO 2 difference, even though that expectation could not be confirmed by recent results [6,7]. Finally, in the era of non-invasive strategies for PE combining several tests of various types, such as clinical evaluation, biological tests, and imaging, the evaluation of a potential role for CO 2 measurement in combination with those other instruments made sense.…”

“…Finally, in the era of non-invasive strategies for PE combining several tests of various types, such as clinical evaluation, biological tests, and imaging, the evaluation of a potential role for CO 2 measurement in combination with those other instruments made sense. Numerous studies are available, and although none to date has been able to prove the safety of such a non-invasive strategy incorporating capnography with a high enough level of evidence to allow its recommendation in daily clinical practice, the venue remains interesting [7-11]. …”

D-Dimer and Exhaled CO2/O2 to Detect Segmental Pulmonary Embolism in Moderate-Risk Patients

“…The alveolar dead space can be estimated by simultaneously measuring the exhaled CO 2 and arterial blood partial pressure of CO 2 (12). The alveolar dead space can significantly improve the diagnostic performance of the D-dimer as a screening tool for PE in the emergency department (ED) setting (12)(13)(14)(15). However, the requirement…”