Use of the alveolar dead space fraction (Vd/Vt) and plasma D-dimers to exclude acute pulmonary embolism in ambulatory patients

Jeffrey A. Kline, Suzy Meek, Dawn Boudrow, Douglas Warner, Stephen Colucciello

Research output: Contribution to journalArticle

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Abstract

Objective: To evaluate the utility of a modified calculation of the alveolar dead space fraction (Vd/Vt), combined with plasma D-dimers, to aid in the exclusion of acute pulmonary embolism (PE). Methods: A prospective comparison of screening modalities was performed in a metropolitan teaching ED. Ambulatory patients evaluated for PE underwent simultaneous end-tidal CO2 and arterial blood gas determinations, as well as venous latex- agglutination D-dimer quantification. The modified Bohr equation was used to calculate Vd/Vt as an index of alveolar dead space. Acute PE was diagnosed or excluded using appropriate combinations of clinical suspicion, ventilation- perfusion lung scanning, lower-extremity venous Doppler ultrasonography, pulmonary angiography, and comprehensive follow-up. Results: Of 170 subjects studied, PE was confirmed (PE+) in 26 (15%) and excluded (PE-) in 144 (85%). In the PE+ group, Vd/Vt was 0.31 ± 0.13 (mean ±SD), and in the PE- group, Vd/Vt was 0.06 ± 0.10 (p < 0.05, t-test). Regarding false-negative rates, Vd/Vt was normal (i.e., <0.2) in 3/26 PE+ patients and D-dimer concentrations were normal (<0.5 μg/L) in 4/26 patients in the PE+ group. The combination of a normal Vd/Vt and D-dimer concentration was 100% sensitive (95% CI = 88- 100%) in excluding PE. False-positive testing (either test positive) occurred in 49/144 subjects (specificity 65%, 95% CI = 52-73%). The age-adjusted alveolar-arterial O2 gradient was 33 ± 38 torr in the PE+ group vs 13 ± 37 tort in the PE-group (p = 0.11). Conclusions: In ambulatory patients, the finding of Vd/Vt <0.2 and D-dimers <0.5 μg/L lowers the probability of acute PE.

Original languageEnglish (US)
Pages (from-to)856-863
Number of pages8
JournalAcademic Emergency Medicine
Volume4
Issue number9
DOIs
StatePublished - Sep 1997

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Keywords

  • Alveolar dead space fraction
  • D-directs
  • Diagnosis
  • Outpatient
  • Pulmonary embolism

ASJC Scopus subject areas

  • Emergency Medicine

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