How Common is Pulmonary Embolism in Patients with COPD Exacerbations?
Abstract & Commentary
By David J. Pierson, MD, Editor, Professor, Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, Seattle, is Editor for Critical Care Alert.
Synopsis: In a selected population of patients with known COPD who were hospitalized with acute worsening of respiratory symptoms but did not have usual signs of an infection or other specific process, 25% were found to have pulmonary embolism.
Source: Tillie-Leblond I, et al. Pulmonary embolism in patients with unexplained exacerbation of chronic obstructive pulmonary disease: prevalence and risk factors. Ann Intern Med. 2006;144:390-396.
In this study from the University Hospital A Calmette in Lille, France, patients with known COPD who were admitted because of acute respiratory deterioration were evaluated for inclusion in a prospective investigation of the prevalence and risk factors for pulmonary thromboembolism (PE) in this setting. Patients who required intubation were excluded, as were all who had purulent sputum, a history of cold or sore throat, a discrepancy between radiographic findings and the clinical picture, severe hypoxemia, pneumothorax, or "iatrogenic intervention" (not further defined). Patients who had none of these exclusionary features underwent spiral computed tomography angiography and venous ultrasonography, and if either of these was positive the patient was classified as having PE. The investigators recorded demographic and clinical data and calculated the probability of PE using the Geneva score. This score correlates the risk of PE with age, previous PE or deep-vein thrombosis, recent surgery, heart rate, arterial PO2 and PCO2, and selected findings on chest radiograph.1
During the 45-month study, 211 patients met the entry criteria, of whom 197 had complete data and form the basis of the article. Two-thirds of them were admitted from the emergency department and one-third were already in the hospital at the time of referral. One hundred-sixty of 197 patients had had pulmonary function tests within 3 months prior to admission, and their mean FEV1 was 1.56 L (52% of predicted). Mean admission arterial PO2 and PCO2 values off supplemental oxygen were 62 and 42 mm Hg, respectively; 29% of the patients had known underlying malignancy.
Forty nine of the 197 patients (25%) met the diagnostic criteria for PE. Clinical factors associated with a statistically significant increased risk for PE were prior PE (risk ratio, 2.43), malignant disease (RR, 1.82), and a decrease in admission PCO2 of at least 5 mm Hg compared with previous measurements (RR, 2.10). Among the 197 patients, 9.2% who had a low Geneva score, indicating a low probability of PE, turned out to have PE (95% confidence interval, 4.7%-15.9%). The authors calculated the likelihood of PE substituting malignant disease for recent surgery in the Geneva score, and postulated that this might increase its predictive ability.
Commentary
One-fourth of the COPD patients in this study who were admitted with a severe exacerbation without another obvious cause were found to have PE. The diagnosis of PE was more likely to be made among patients with previous thrombosis, underlying malignancy, or an admission PCO2 at least 5 mm Hg below their baseline value. What can these findings tell us about the likelihood of PE among the patients we manage with COPD exacerbations, or whether we should include a CT angiogram or Doppler study in our admission evaluation of such patients? In my opinion, the answer is "that depends."
From a clinician's perspective there are some unfortunate omissions in this paper. We are not told how many patients were admitted to the authors' unit with COPD exacerbations during the study period, or what proportion of them were considered not to have an infection or other specific cause and were thus referred for possible inclusion. Most COPD patients presenting with an exacerbation have features suggesting infection, and such patients were not included in this study. In fact, the widely used Anthonisen criteria2 for determining whether a severe exacerbation is present rely on sputum volume and purulence in addition to an increase in dyspnea for the definition. The study also excluded the most severely ill patients, those requiring intubation and mechanical ventilation. Thus, the patients in this study may have represented a minority of the COPD exacerbations seen at the authors' institution during the study period.
These patients were also not the "end-stage" patients in whom many exacerbations occur. Most of them would be classified as Stage II or III by the GOLD criteria, based on their baseline FEV1 values. Their exacerbations would not have been judged severe by blood gas criteria: arterial pH values are not provided, but mean admission PCO2 42 mm Hg and PO2 62 mm Hg breathing room air would not be expected in many patients presenting with severe exacerbations. In addition, the paper does not include hospital length-of-stay or mortality data on the patients. Thus, clinicians attempting to apply this study's findings to their own practices need to be aware of the selected nature of the patients who were included.
For me, the take-home message of this study is that when patients with known COPD present with an acute clinical deterioration and do not have the usual features of a severe exacerbation, PE should be considered-especially if they have a known malignancy, a history of thrombosis, or an arterial PCO2 lower rather than higher than expected. The prevalence of PE in the general population of COPD patients presenting with an exacerbation cannot be determined from this study.
References
- Wicki J, et al. Assessing clinical probability of pulmonary embolism in the emergency ward: a simple score. Arch Intern Med. 2001;161:92-97.
- Anthonisen NR, et al. Antibiotic therapy in exacerbations of chronic obstructive pulmonary disease. Ann Intern Med. 1987;106:196-204.
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