1560 Canadian Family Physician•Le Médecin de famille canadien❖VOL 47: AUGUST • AOÛT 2001
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Emergency Case
Harold Schubert, MD, MSC, CCFP
Dr Schubert practises emergency medicine at the University of British Columbia Hospital Site of Vancouver Hospital.
QUESTIONS
A young man who had recently returned from Asia on a long aircraft flight came to the emergency department complaining of shortness of breath on exertion. What are the risk factors for pulmonary embolism (PE)? What signs and symptoms are specific for PE? What tests are best?
Pulmonar y embolism is not a unique disease process but a highly lethal complication of deep vein thrombosis (DVT). Annual incidence of PE in North America probably exceeds a million cases.1 Pulmonar y embolism is second only to coronar y artery disease as a cause of sudden unexpected death at any age.1In 80% of fatal cases, PE is not diagnosed until autopsy; in more than half of these cases, there is evidence of previous PE.1Patients who survive PE are at high risk of recurrent PE and development of pulmonary hypertension. Prompt diagnosis and treat- ment can dramatically reduce morbidity and mortality.
Despite improvements in diagnosis and treatment of DVT, there has been no change in the incidence of PE during the past 30 years.1 The main challenge is that DVT and PE are most often clinically silent and do not manifest readily recognizable symptoms and signs.1,2
Pathophysiology
Venous thrombosis is the initial event in all patients who subsequently have PE. Risk factors for PE are the same as for DVT and have been discussed in a previous Emergency Case.3 Most (85% to 90%) PE results from DVT of the leg veins.1
Clinical features
The first large prospective multicentre study of PE, the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED), was done in 1985 and 1986.2,4
More than 5500 patients with symptoms and signs sug- gesting PE were enrolled in the PIOPED study, which evaluated symptoms, signs, arterial blood gases, elec- trocardiograms, chest x-ray films, ventilation-perfusion (V/Q) scans, and other features. More than 750 patients had both V/Q scans and pulmonary angiogra- phy. The PIOPED study served to dispossess physi- cians of inaccurate notions about the clinical diagnosis of PE and is the source of all the following information.
The classic triad of dyspnea, chest pain, and hemoptysis occurs in less than 20% of patients with PE.1,2Most patients with those symptoms and signs have a disease other than PE to account for them.
Table 1 shows the frequency with which symptoms and signs occurred in patients with PE and without PE who did not have pre-existing pulmonary or car- diac disease.2Because many cases of PE are clinically silent, the reported incidence of symptoms and signs in patients with PE is overstated.
Patients eventually diagnosed with PE might pre- sent with dyspnea, hemoptysis, chest pain or chest wall tenderness, upper back or shoulder pain, abdomi- nal pain, syncope, seizure, fever, productive cough, new onset of reactive air way disease, hiccups, new onset of atrial fibrillation, or any of a host of other symptoms and signs.1 Physicians’ suspicion of PE must remain high for any patient with chest symp- toms or signs not explained by another diagnosis.
Diagnostic tests
Arterial blood gas analysis with particular attention to the A-a gradient has long been a standard test for sus- pected PE. The A-a gradient is, however, nonspecific for PE.2,5An abnormal gradient is more likely due to another condition that mimics PE, such as chronic obstructive pulmonary disease, pneumonia, or conges- tive heart failure. The PIOPED study found a PO2 of
Diagnosing pulmonary embolism
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> 80 mm Hg in 26% of patients with proven PE, and 6%
of those had a normal A-a gradient. Pulse oximetry is similarly not diagnostic for PE. Physicians should be cautious not to exclude PE on the basis of normal oximetr y, PO2, or A-a gradient. Measurement of D- dimer holds promise, but the testing method currently used in most hospitals (latex agglutination) is not sen- sitive enough to be reliable.5,6
The most common abnormalities seen on chest x-ray examination in proven PE were atelectasis or parenchymal abnormalities (68%), pleural ef fusion (48%), pleural-based opacity (35%), elevated hemidi- aphragm (24%), decreased pulmonar y vascularity (21%), prominent central pulmonary artery (15%), and cardiomegaly (12%). All these findings had a high degree of overlap with x-ray findings for patients with- out PE (ie, x-ray findings are nonspecific5). The “clas- sic” chest x-ray findings of Wester mark sign (prominent central pulmonar y vessels and smaller peripheral vessels) and Hampton hump (a triangular or rounded pleural-based infiltrate with the apex pointing to the hilum) are uncommon.5
Electrocardiographic abnormalities most com- mon in PE were nonspecific ST-segment and T-wave changes (49%). Electrocardiographic findings were normal for 30% of patients; 90% showed normal sinus rhythm.5
Ventilation-perfusion (V/Q) scan is currently the recommended test when PE is suspected, and is a good test for young patients without existing lung dis- ease. Unfortunately, incidence of PE increases with age, as does incidence of other lung disease, so many scans of high-risk patients are nondiagnostic. In the PIOPED study, 41% of patients with angiographically proven PE had V/Q scan results indicating a high probability of disease, while 48% with negative results of angiography had V/Q scan results indicating high or intermediate probability. Sensitivity is about 97%, but specificity overall is only about 10%.4
Spiral contrast computed tomography scan has advantages over V/Q scan. It is very fast and thought to be quite sensitive and specific; CT can provide valu- able information about possible alternative diagnoses that V/Q scan cannot.5,7 In some centres, CT has become the test of choice, but the accuracy and role of CT in this enigmatic condition have not been clearly established.
Echocardiography (transthoracic or trans- esophageal) can be a useful bedside test for critically ill PE patients.6 Anatomic changes resulting from increased pulmonary pressure can be assessed, and clots can be visualized in heart chambers and large pul- monary vessels. A role for this test has not been estab- lished; technical expertise is frequently unavailable.
When PE is suspected but V/Q scan is not diagnos- tic, what should physicians do next? Recalling that most PE arises from leg DVT and that most DVT is clinically silent, searching for DVT with venous Doppler ultrasound is an appropriate next step.5,6If PE is present, DVT will be found in about 50% of cases.
Pulmonar y angiography remains the criterion standard diagnostic test for PE and is the final resort if PE is strongly suspected and the diagnosis cannot be made by other means. Aside from requiring high technical expertise, the test is invasive and associated with substantial morbidity and mortality.5,6
Most valuable tool
Making the diagnosis of PE is difficult. Hope rests with having high suspicion for PE in any patient pre- senting with chest symptoms not explained by another diagnosis. Physicians must be aware of the limitations of current test methods and be careful not to exclude a diagnosis of PE on the basis of insensitive or non- specific tests.
Our success rate in diagnosing PE (before autopsy) is abysmal. Better tests are needed. Currently, our
INDICATION WITH PE (%) WITHOUT PE (%)
S Y M P T O M S Dyspnea Pleuritic pain Cough Leg pain Hemoptysis
7 3 6 6 3 7 2 6 1 3
7 2 5 9 3 6 2 4 8 S I G N S
Tachypnea Tachycardia Fever >38.5°C Signs of deep vein thrombosis
7 0 3 5 7 1 1
6 8 2 4 1 2 1 1
Chest x-ray abnormality*
8 4 6 6
Abnormal A-a gradient
8 6 7 8
Table 1.Frequency of symptoms and signs in patients with and without pulmonar y embolism (PE)
Data from Stein et al2and Janata-Schwatczek et al.5 Difference statistically significant for this test only.
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most valuable diagnostic tool is high clinical suspicion.
Answers
Pulmonary embolism is a complication of DVT; risk factors are the same. Clinical presentation of PE is highly variable; no symptoms, signs, blood tests, chest x-ray findings, or ECG changes are typical or specific. High clinical suspicion is essential.
Ventilation-perfusion scan is often nondiagnostic but is the current test of choice; CT appears promising for this purpose. Pulmonary angiography remains the criterion standard test and is a last resort if diagnosis cannot be confirmed by other means.
References
1. Feied C, Handler JA. Pulmonary embolism. Emed J 2001;2(5). Updated 2001 May 12. Available at http://www.emedicine.com/emerg. Accessed 2001 May 28.
2. Stein PD, Terrin ML, Hales CA, Palevsky HI, Saltzman HA, Thompson BT, et al.
Clinical, laboratory, roentgenographic and electrocardiographic findings in patients with acute pulmonary embolism and no pre-existing cardiac or pulmonary disease.
Chest1991;100(3):598-603.
3. Schubert H. Deep vein thrombosis [Emergency Case]. Can Fam Physician 2001;47:45-7.
4. PIOPED investigators. Value of the ventilation/perfusion scan in acute pulmonary embolism. JAMA 1990;263(20):2753-9.
5. Janata-Schwatczek K, Weiss K, Riezinger I, Bankier A, Domanovits H, Seidler D.
Pulmonary embolism. II. Diagnosis and treatment. Semin Thromb Hemost 1996;22(1):33-52.
6. Perrier A, Junod AF. Has the diagnosis of pulmonary embolism become easier to establish? Respir Med 1995;89:241-51.
7. Holbert MJ, Costello P, Federle MP. Role of spiral computed tomography in the diagnosis of pulmonary embolism in the emergency department. Ann Emerg Med 1999;33(5):520-8.
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