Measurement of expired carbon dioxide, oxygen and volume in conjunction with pretest probability estimation as a method to diagnose and exclude pulmonary venous thromboembolism

Am J Respir Crit Care Med

Hogg

Courtney³

et al. 2010

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Rationale: Pulmonary embolism (PE) decreases the exhaled end-tidal ratio of carbon dioxide to oxygen (etCO 2 /O 2 ). Objectives: To test if the etCO 2 /O 2 can produce clinically important changes in the probability of segmental or larger PE on computerized tomography multidetector-row pulmonary angiography (MDCTPA) in a moderate-risk population with a positive D-dimer. Methods: Emergency department and hospitalized patients with one or more predefined symptoms or signs, one or more risk factors for PE, and 64-slice MDCTPA enrolled from four hospitals. D-dimer greater than 499 ng/ml was test (1), and D-dimer less than 500 ng/ml was test(2). The median etCO 2 /O 2 less than 0.28 from seven or more breaths was test(1) and etCO 2 /O 2 greater than 0.45 was test(2). MDCTPA images were read by two independent radiologists and the criterion standard was the interpretation of acute PE by either reader. PE size was then graded. Measurements and Main Results: We enrolled 495 patients, including 60 (12%) with segmental or larger, and 29 (6%) with subsegmental PE. A total of 367 (74%) patients were D-dimer(1), including all 60 with segmental or larger PE (posterior probability 16%). The combination of D-dimer(1) and etCO 2 /O 2 (1) increased the posterior probability of segmental or larger PE to 28% (95% confidence interval [CI] for difference of 12%, 3.0-22%). The combination of D-dimer(1) and etCO 2 /O 2 (2) was observed in 40 patients (8%; 95% CI, 6-11%), and none (0/40; 95% CI, 0-9%) had segmental or larger PE on MDCTPA. No strategy changed the prevalence of subsegmental PE. Conclusions: In moderate-risk patients with a positive D-dimer, the et etCO 2 /O 2 less than 0.28 significantly increases the probability of segmental or larger PE and the etCO 2 /O 2 greater than 0.45 predicts the absence of segmental or larger PE on MDCTPA. Clinical trial registered with www.clinicaltrials.gov (NCT 00368836).

Section: Discussionmentioning

confidence: 56%

Section: What This Study Adds To the Fieldmentioning

confidence: 99%

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

Am J Respir Crit Care Med

Hogg

Courtney³

et al. 2010

Self Cite

“…This study was a secondary analysis of five discrete databases [18][19][20][21][22] collected at 15 hospitals in three countries between 2001 to 2006. The study protocol was approved by the institutional review boards for the conduct of research on humans of all participating hospitals.…”

Section: Methodsmentioning

confidence: 99%

“…The methods and patient characteristics of two of these databases have been published, 19,20 with only partial data from one database (from coauthor MPT) used for one study. 18 The largest of these databases was explicitly collected for this purpose, and the methods of data collection have also been published.…”

Section: Study Setting and Populationmentioning

confidence: 99%

Accuracy of Very Low Pretest Probability Estimates for Pulmonary Embolism Using the Method of Attribute Matching Compared with the Wells Score

Academic Emergency Medicine

Courtney

Than

et al. 2010

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Objectives: Attribute matching matches an explicit clinical profile of a patient to a reference database to estimate the numeric value for the pretest probability of an acute disease. The authors tested the accuracy of this method for forecasting a very low probability of venous thromboembolism (VTE) in symptomatic emergency department (ED) patients. Methods:The authors performed a secondary analysis of five data sets from 15 hospitals in three countries. All patients had data collected at the time of clinical evaluation for suspected pulmonary embolism (PE). The criterion standard to exclude VTE required no evidence of PE or deep venous thrombosis (DVT) within 45 days of enrollment. To estimate pretest probabilities, a computer program selected, from a large reference database of patients previously evaluated for PE, patients who matched 10 predictor variables recorded for each current test patient. The authors compared the outcome frequency of having VTE [VTE(+)] in patients with a pretest probability estimate of <2.5% by attribute matching, compared with a value of 0 from the Wells score.Results: The five data sets included 10,734 patients, and 747 (7.0%, 95% confidence interval [CI] = 6.5% to 7.5%) were VTE(+) within 45 days. The pretest probability estimate for PE was <2.5% in 2,975 of 10,734 (27.7%) patients, and within this subset, the observed frequency of VTE(+) was 48 of 2,975 (1.6%, 95% CI = 1.2% to 2.1%). The lowest possible Wells score (0) was observed in 3,412 (31.7%) patients, and within this subset, the observed frequency of VTE(+) was 79 of 3,412 (2.3%, 95% CI = 1.8% to 2.9%) patients.Conclusions: Attribute matching categorizes over one-quarter of patients tested for PE as having a pretest probability of <2.5%, and the observed rate of VTE within 45 days in this subset was <2.5%.ACADEMIC EMERGENCY MEDICINE 2010; 17:133-141 ª

“…Several studies have been conducted utilizing the knowledge that pulmonary embolism increases pulmonary deadspace and affects partial pressures of exhaled CO 2 or O 2 [11,20]. Recently, development of a portable device that measures exhaled CO 2 and O 2 concentrations along with flows and volumes has shown promise in predicting thromboembolism [12].…”

Section: Introductionmentioning

confidence: 99%

Use of genetic programming to diagnose venous thromboembolism in the emergency department

Engoren

Genet Program Evolvable Mach

2007

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Pulmonary thromboembolism as a cause of respiratory complaints is frequently undiagnosed and requires expensive imaging modalities to diagnose. The objective of this study was to determine if genetic programming could be used to classify patients as having or not having pulmonary thromboembolism using exhaled ventilatory and gas indices as genetic material. Using a custom-built exhaled oxygen and carbon dioxide analyzer; exhaled flows, volumes, and gas partial pressures were recorded from patients for a series of deep exhalation and 30 s tidal volume breathing. A diagnosis of pulmonary embolism was made by contrast-enhanced computerized tomography angiography of the chest and indirect venography supplemented by 90-day follow-up. Genetic programming developed a series of genomes comprising genes of exhaled CO 2 , O 2 , flow, volume, vital signs, and patient demographics from these data and their predictions were compared to the radiological results. We found that 24 of 178 patients had pulmonary embolism. The best genome consisted of four genes: the minimum flow rate during the third 30 s period of tidal breathing, the average peak exhaled CO 2 during the first 30 s period of tidal breathing, the average peak of the exhaled O 2 during the first 30 s period of tidal breathing, and the average peak exhaled CO 2 during the fourth period of tidal breathing, which immediately followed a deep exhalation. This had 100% sensitivity and 91% specificity on the construction population and 100% and 82%, respectively when tested on the separate validation population. Genetic programming using only data obtained from exhaled breaths was very accurate in classifying patients with suspected pulmonary thromboembolism.