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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 CO, 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 2 SD), and in the PE-group, Vd/Vt was 0.06 t-0.10 (p c 0.05, t-test). Regarding false-negative rates, Vd/Vt was normal (i.e., c0.2) in 3/26 PE+ patients and D-dimer concentrations were normal (~0 . 5 pg/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. Falsepositive testing (either test positive) occurred in 49/14 subjects (specificity 65%, 95% CI = 52-73%). The age-adjusted alveolar-arterial O2 gradient was 33 5 38 torr in the PE+ group vs 13 2 37 torr in the PEgroup (p = 0.1 1). Conclusions: In ambulatory patients, the finding of Vd/Vt ~0 . 2 and D-dimers c0.5 pg/L lowers the probability of acute PE.

Background: Clinicians in outpatient clinics and emergency departments desire an accurate quantitative Ddimer assay. The study objective was to evaluate the diagnostic performance characteristics of the latex turbidimetric D-dimer test in the diagnosis of pulmonary embolism (PE) in the emergency department population. Methods: We conducted a search of MEDLINE, EM-BASE, and bibliographies of previous systematic reviews with no language restriction. Experts in the field of PE research were contacted to identify unpublished studies. Prospective investigations involving predominately outpatient populations with suspected PE that used a turbidimetric D-dimer test were included. Two authors extracted data independently and assessed study quality based on the composition of the patient spectrum and the reference standard used. Consensus was reached by conference. The analysis was based on a summary ROC curve and combining sensitivity and specificity independently across studies using a random-effects model. Results: The search yielded 264 publications and 2 unpublished studies. Nine studies met the inclusion criteria and provided a sample of 1901 individuals. Eight of the nine studies were homogeneous in terms of both sensitivity and specificity. One study had similar sensitivity but higher specificity. Combining the studies yielded an overall sensitivity of 0.93 (95% confidence interval, 0.89 -0.96) and an overall specificity of 0.51 (95% confidence interval, 0.42-0.59).

For patients with positive MRI at the time of their initial neurologic event, both gadolinium-enhancing lesions and the Barkhof criteria are predictors for development of CDMS over a short interval. However, these results, based on a combined CDMS/MRI outcome, suggest that the majority of these patients are already in the earliest stages of MS, regardless of whether any further MRI criteria are met.

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