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Splendors and miseries of expired CO2 measurement in the suspicion of pulmonary embolism.
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PMID:  20156311     Owner:  NLM     Status:  MEDLINE    
Capnography has been studied for decades as a potential diagnostic tool for suspected pulmonary embolism. Despite technological refinements and its combination with other non-invasive instruments, no evidence to date allows recommending the use of expired carbon dioxide measurement as a rule-out test for pulmonary embolism without additional radiological testing. Further investigations are, however, still warranted.
Franck Verschuren; Arnaud Perrier
Publication Detail:
Type:  Comment; Letter     Date:  2010-01-27
Journal Detail:
Title:  Critical care (London, England)     Volume:  14     ISSN:  1466-609X     ISO Abbreviation:  Crit Care     Publication Date:  2010  
Date Detail:
Created Date:  2010-05-18     Completed Date:  2010-09-15     Revised Date:  2011-07-20    
Medline Journal Info:
Nlm Unique ID:  9801902     Medline TA:  Crit Care     Country:  England    
Other Details:
Languages:  eng     Pagination:  110     Citation Subset:  IM    
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MeSH Terms
Breath Tests*
Carbon Dioxide / analysis*
Pulmonary Embolism / diagnosis*
Reg. No./Substance:
124-38-9/Carbon Dioxide
Comment On:
Crit Care. 2009;13(6):R196   [PMID:  19995420 ]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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Journal ID (nlm-ta): Crit Care
ISSN: 1364-8535
ISSN: 1466-609X
Publisher: BioMed Central
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Copyright ©2010 BioMed Central Ltd
Print publication date: Year: 2010
Electronic publication date: Day: 27 Month: 1 Year: 2010
pmc-release publication date: Day: 27 Month: 1 Year: 2011
Volume: 14 Issue: 1
First Page: 110 Last Page: 110
ID: 2875509
Publisher Id: cc8838
PubMed Id: 20156311
DOI: 10.1186/cc8838

Splendors and miseries of expired CO2 measurement in the suspicion of pulmonary embolism
Franck Verschuren1 Email:
Arnaud Perrier2 Email:
1Université Catholique de Louvain, Cliniques universitaires Saint-Luc, Acute Medicine Department, Accidents and Emergency Unit, avenue Hippocrate, 1200 Brussels, Belgium
2Division of General Internal Medicine, Geneva University Hospital and Faculty of Medicine, 4, rue Gabrielle-Perret-Gentil, CH-1211 Geneva 14, Switzerland

In the previous issue of Critical Care, Rumpf and colleagues [1] evaluated the potential contribution of measuring end-tidal carbon dioxide (CO2) for suspected pulmonary embolism (PE) in the prehospital setting. Capnography has been studied for decades as a potential diagnostic tool for patients with suspected PE. Indeed, PE is expected to create areas of reduced arterial flow with normal or increased alveolar ventilation, resulting in increased alveolar dead space volume and reduced global expired CO2. This should create a difference between arterial and end-tidal CO2 values, as first demonstrated by Robin and colleagues [2] in 1959. However, during the two following decades, several authors pointed out the numerous pitfalls and sources of errors in assessing the arterial to end-tidal CO2 difference in the clinical suspicion of PE, and this test was finally abandoned until the nineties [3-5].

Three elements explain the current resurgence of expired CO2 measurement in the suspicion of PE. First, technical improvements now allow measuring CO2 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 CO2 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 CO2 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 CO2 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].

Where then can we place the endeavor of Rumpf and colleagues? They included 131 consecutive patients suspected of PE who had an abnormal rapid point-of-care D-dimer result in a prehospital setting and evaluated them with a combination of clinical probability of PE (two-level Wells score) and measurement of the end-tidal partial pressure of CO2 (PCO2). PE was diagnosed in the emergency department by a positive spiral computed tomography, a high-probability V/Q scan, or a positive pulmonary angiogram. The combination of a normal end-tidal CO2 value (defined as higher than 28 mm Hg based on a receiver operating characteristic analysis) and an unlikely probability of PE had a 100% sensitivity and 100% negative predictive value (95% confidence interval [CI] 90% to 100%) for ruling out PE. In contrast, the association of a low end-tidal CO2 value (less than 28 mm Hg) and a high clinical probability had only an 86% positive predictive value for PE, and further tests would certainly be required in such patients. Clearly, those results are preliminary. This is a small series and it was designed to set the cutoff value for this particular capnography technique and assess its feasibility in the field. Moreover, as acknowledged by the authors themselves, the clinicians who established the diagnosis were not blinded to either clinical assessment or capnography results. Finally, the prevalence of PE is unusually high, although this would tend to bias the results toward lower, not higher, sensitivity. But the sheer simplicity of the technique used by Rumpf and colleagues [1] is appealing and certainly deserves validation in a large-scale prospective study. Indeed, it emphasizes the use of expired CO2 alone without associated arterial PCO2, and this is a pragmatic issue in modern emergency medicine [12]. Also, the use of capnography in the prehospital setting is interesting: there might be situations in which a rapid and rough evaluation of the patient's expired CO2 status would help emergency physicians in making vital decisions, such as starting thrombolysis for a suspected fulminant PE, as well as in monitoring the hemodynamic effect of thrombolysis in such patients [13].

Finally, the merit of the article by Rumpf and colleagues [1] is to remind us that clinical applications of capnography are still growing, especially amongst spontaneously breathing patients. Physicians dealing with acute medicine should make every effort to become familiar with expired CO2 measurement. Inconclusive capnographic results related to tachypneic or apprehensive patients do not overcome the potential for expired CO2 to be placed inside the diagnostic algorithm of a challenging disease like PE.


CO2: carbon dioxide; PCO2: partial pressure of carbon dioxide; PE: pulmonary embolism.

Competing interests

The authors declare that they have no competing interests.

Rumpf TH,Križmarić M,Grmec S,Capnometry in suspected pulmonary embolism with positive D-dimer on the fieldCrit CareYear: 200913R19610.1186/cc819719995420
Robin ED,Julian DG,Travis DM,Crump CH,A physiological approach to the diagnosis of acute pulmonary embolismN Engl J MedYear: 195958659113632933
Nutter DO,Massumi RA,The arterial-alveolar carbon dioxide tension gradient in diagnosis of pulmonary embolusDis ChestYear: 19665038038710.1378/chest.50.4.3805924974
Vereerstraeten J,Schoutens A,Tombroff M,De Koster,Value of measurement of alveolo-arterial gradient of PCO2 compared to pulmonary scan in diagnosis of thromboembolic pulmonary diseaseThoraxYear: 197328306312472449810.1136/thx.28.3.306
Colp C,Stein M,Re-emergence of an "orphan" test for pulmonary embolismChestYear: 20011205610.1378/chest.120.1.511451804
Patel MM,Rayburn DB,Browning JA,Kline JA,Neural network analysis of the volumetric capnogram to detect pulmonary embolismChestYear: 19991161325133210.1378/chest.116.5.132510559095
Verschuren F,Sanchez O,Righini M,Heinonen E,Le Gal G,Meyer G,Perrier A,Thys F,Volumetric or time-based capnography for excluding pulmonary embolism in outpatients?J Thromb HaemostYear: 2010860671987445710.1111/j.1538-7836.2009.03667.x
Kline JA,Israel EG,Michelson EA,O'Neil BJ,Plewa MC,Portelli DC,Diagnostic accuracy of a bedside D-dimer assay and alveolar dead-space measurement for rapid exclusion of pulmonary embolism: a multicenter studyJAMAYear: 200128576176810.1001/jama.285.6.76111176914
Rodger MA,Jones G,Rasuli P,Raymond F,Djunaedi H,Bredeson CN,Wells PS,Steady-state end-tidal alveolar dead space fraction and D-dimer: bedside tests to exclude pulmonary embolismChestYear: 200112011511910.1378/chest.120.1.11511451825
Rodger MA,Bredeson CN,Jones G,Rasuli P,Raymond F,Clement AM,Karovitch A,Brunette H,Makropoulos D,Reardon M,Stiell I,Nair R,Wells PS,The bedside investigation of pulmonary embolism diagnosis study: a double-blind randomized controlled trial comparing combinations of 3 bedside tests vs ventilation-perfusion scan for the initial investigation of suspected pulmonary embolismArch Intern MedYear: 200616618118710.1001/archinte.166.2.18116432086
Sanchez O,Wermert D,Faisy C,Revel MP,Diehl JL,Sors H,Meyer G,Clinical probability and alveolar dead space measurement for suspected pulmonary embolism in patients with an abnormal D-dimer test resultJ Thromb HaemostYear: 200641517152210.1111/j.1538-7836.2006.02021.x16839348
Kline JA,Hogg M,Measurement of expired carbon dioxide, oxygen and volume in conjunction with pretest probability estimation as a method to diagnose and exclude pulmonary venous thromboembolismClin Physiol Funct ImagingYear: 20062621221910.1111/j.1475-097X.2006.00672.x16836693
Verschuren F,Heinonen E,Clause D,Roeseler J,Thys F,Meert P,Marion E,El Gariani A,Col J,Reynaert M,Liistro G,Volumetric capnography as a bedside monitoring of thrombolysis in major pulmonary embolismIntensive Care MedYear: 2004302129213210.1007/s00134-004-2444-915378240

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