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Evidence in the ED

Evidence in the ED. The Utility of Arterial Blood Gas In the Setting of Pulmonary Embolism Rex Mathew, MD. Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). Landmark study investigating diagnosis of PE

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Evidence in the ED

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  1. Evidence in the ED The Utility of Arterial Blood Gas In the Setting of Pulmonary Embolism Rex Mathew, MD

  2. Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) • Landmark study investigating diagnosis of PE • The PIOPED investigators. Value of the ventilation/perfusion scan in acutepulmonary embolism: results of the Prospective Investigation of PulmonaryEmbolism Diagnosis (PIOPED) JAMA 1990.

  3. PIOPED based data • Stein et al. Clinical, laboratory, roentgenographic, and electorcardiographic findings in patients with acute pulmonary embolism and no pre-existing cardiac or pulmonary disease. Chest 1991. • Subset of patients involved in PIOPED study was evaluated and the PaO2 and alveolar-arterial gradients were compared. • Patients with and without PE could NOT be distinguished on the basis of either of these values.

  4. PIOPED based data • Stein et al. Alveolar-arterial oxygen gradient in the assessment of acute PE. Chest, 1995. • Patients were categorized as (1) the entirecohort, (2) no prior cardiopulmonary disease and no prior PE, and (3) no prior PE or deep venous thrombosis. • Normal A-a gradient < 20 mm Hg: 11 to 14% of patients with PE in the three categories of patients had a normal A-a gradient. • Normal A-a gradient = Age/4 plus 4: 8 to 10% of patients with PE in the three categories of patients had a normal A-a gradient. • Age-related values from the literature: 20 to 23% of patients with PE in the three categories of patients had a normal A-a gradient. • Conclusion: Normal values of the A-a gradient did not exclude the diagnosis of acute PE.

  5. PIOPED based data • Stein et al. Arterial blood gas analysis in the assessment of suspected acute pulmonary embolism. Chest, 1996. • Among patients without prior cardiopulmonary disease who had values of the PaO2 and PaCO2 that were not low and a P(A-a)O2 that was normal, 16/42 or 38% (95% CI =24-54%) had PE. • Among patients with prior cardiopulmonary disease who had PaO2 and PaCO2 values that were not low and a P(A-a)O2 that was normal, 4/28 or 14% (95% CI =4-33%) had PE. • Other combinations of blood gas levels and the P(A-a)O2 gradient, failed to exclude PE in larger percentages of patients. • Conclusion: Blood gas levels are of insufficient discriminant value to permit exclusion of the diagnosis of PE.

  6. Pro-ABG Studies • Cvitanic and Marinolooked at A-a gradient with a normal PaCO2 (>36mmHg) inexcluding PE • Cvitanic O, Marino PL. Improved use of arterial blood gas analysis in suspected pulmonary embolism. Chest 1989; 95: 48-51 • McFarlane and Imperiale tried to improve the sensitivityof the A-a gradient in excluding PE by combining it withthe absence of a prior history of thromboembolic disease. • McFarlane MJ, Imperiale TF. Use of the alveolar-arterial oxygen gradient in the diagnosis of pulmonary embolism. Am J Med 1994; 96: 57-62 • Neither study’s rules as reported were 100% sensitive. • Clinicalutility, as measured by the proportion of patients correctly excluded,was either not measured or was low.

  7. Rodger et al. American Journal of Respiratory & Critical Care Medicine, 2000. • Diagnostic value of arterial blood gas measurement in suspected pulmonary embolism. • Two hundred ninety-three consecutive patients referred forimaging to investigate suspected PE were included. • An RR > 20 breaths/min, a PaO2 < 80 mm Hg, aPaCO2< 36 mm Hg, or an abnormal A-a gradient were not predictiveof PE in patients suspected of having PE.

  8. Rodger et al, American Journal of Respiratory & Critical Care Medicine, 2000. • In 1998, Egermayer and colleagues found that the combination of a negative D-dimer test result and a PaO2>80 mm Hg had anegative predictive value of 100% in patients with suspected PE. 40 patients included in this study. • Egermeyer et al, Usefullness of D-dimer, blood gas and respiratory rate measurements for excluding pulmonary embolism. Thorax 1998; 53: 830-834. • Rodgers et al were able to demonstratea negative predictive value of only 91.9% for this clinical predictionrule.

  9. Rodger et al, American Journal of Respiratory & Critical Care Medicine, 2000. • Egermayer also showed that a negative D-dimer, test result,a PaO2 of  80 mm Hg, and an RR < 20 breaths/min also had a negativepredictive value of 100% in patients with suspected PE. • Rodgers et al we were able to demonstrate a negative predictivevalue of only 95% with this rule.

  10. Conclusion • ABG is NOT useful in excluding or confirming the diagnosis of PE.

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