Author: Anu Mitra / Codes: CC21, HAP6, HAP8, RespiC10, RespiP1, RespiP2, RespiP3, RespiP4, SLO1, SLO10 / Published: 05/11/2014
Riaz I, Jacob B., Pulmonary embolism in Bradford, UK: role of end-tidal CO2 as a screening tool., Clin Med. 2014 Apr;14(2)
- Objective: To evaluate whether EtCO2 measurement can be used at the bedside to exclude pulmonary embolism (PE).
- Design: This was a prospective diagnostic study set in a British acute medical admissions ward. Patients suspected of having a PE ie., those with CT pulmonary angiogram (CTPA) were enrolled.
- Tests: The reference test was CTPA. The index test was an oral hand-held capnopgraph. Patients also had Wells scoring done and D-dimers taken in those patients for whom it was indicated. The researcher conducting the capnography was blinded to the CTPA findings.
- Results: 100 patients were enrolled, of whom 38 turned out to have a PE. At cutoff of 450mcg/L D-dimer had sensitivity of 96%, specificity 53%. At a cutoff of 4.3kPa, EtCO2 had a sensitivity of 100%, specificity 68%
- Strengths: A clear, unambiguous design and protocol using a recognised reference standard. There was blinding of the researcher.
- Limitations: Validity – patients weren’t blinded. EtCO2 measured up to 24 hours after admission: ?attrition effect after anticoagulation started. The patients had already been through a selection process ie., Wells/D-dimer, to be referred for CTPA. No sample size calculation.
Generalisability: This is a very different population from the many undifferentiated chest pain/dyspnoea/haemoptysis/collapse cases we see in the ED. This is a higher prevalence population. Positive predictive value would be even lower in the lower prevalence population, although negative predictive value would remain high. Also question marks remain about the reliability of the test itself. Is it accurate if nasal prongs aren’t used?
- Summary: This is a well-designed paper. Results are interesting and have reasonable validity for an acute medical admissions population. We think this paper demonstrated proof of concept.
- Will it change our practice? As Emergency Physicians we don’t think this has quite enough external validity – what I call the “so what factor” – for us to adopt it wholesale. It may have a place as a quick ‘rule-out’ test at triage prior to deciding upon doing Wells/D-dimer, and may be more effective than the PERC score as it is not dependent upon age. We would recommend a similar study performed on our undifferentiated ED population.
|Anu Mitra||Catherine Gant|
|Talking about Riaz and Jacob|
|Background: Pulmonary Embolism Keeps Emergency Physicians Up At Night|
|So this sounds like a very important study then! Shall we go through it?|
|Objective: To evaluate whether EtCO2 can be used to exclude PE at the bedside|
|Limitations Internal Validity
|Will It Change Our Practice?|