Missed PE represents a dangerous event for both patients and physicians. Most cases of fatal PE go unrecognized before death.73
Contrary to the expectations of many practitioners, PE may present with isolated dyspnea.74-76
Isolated dyspnea is one of the most common symptoms in ambulatory patients with PE.40
In ED patients
with PE, one-third report dyspnea without chest pain. This may be due to the fact that nearly half of ambulatory patients with PE have multiple emboli that do not result in lung infarction. Lung infarction is the primary cause of the pain associated with PE.77
In contrast, most hospitalized patients with PE (80- 90%) have painful dyspnea.18,78
This pulmonary infarction syndrome, characterized by painful dyspnea (and often hemoptysis), will usually demonstrate an infiltrate on chest x-ray.18
In a study of ambulatory patients, only two out of 26 of those with PE had symptoms and radiographic findings consistent with pulmonary infarction, compared to the 70-90% of hospitalized patients with PE.77,78
The diagnosis of PE is difficult for many reasons, not the least of which is its variable presentation. Some patients may have dramatic findings such as cyanosis and shock, while others may present with mild dyspnea. 79
Few bedside tests can eliminate the diagnosis of PE. Patients may have a normal PO2
by pulse oximetry or arterial blood gas.
Even a normal A-a DO2
gradient does not rule out PE; 15% of patients with angiographically proven pulmonary emboli will have a normal gradient.40,80-82
Young patients with emboli are especially likely to demonstrate normal oxygenation. In patients younger than 40 years of age, nearly 25% will have a normal A-a DO2
The A-a DO2
gradient is normal in more than half of pregnant patients with emboli.84
In older patients, the age-adjusted A-a DO2
gradient is 94% sensitive for PE but only 9% specific.83
A chest film is necessary in all patients with suspected PE. It helps the radiologist interpret other studies, such as the V/Q scan, and may provide an alternative diagnosis (pneumothorax). Nearly 80% of patients with PE have abnormal chest films.85
The most common findings include pleural effusion and infiltrate.
The V/Q scan is the most well-validated screening test for PE. A high-probability scan in conjunction with a high clinical probability is 97% specific for PE.41
If the perfusion portion of the scan is homogeneous (normal), regardless of the ventilation pattern, it excludes PE.41
Note the word "normal." Minor abnormalities or "nearnormal" scans do not have this sensitivity. Acute Bronchitis
Acute bronchitis is defined as cough productive of sputum in a patient with no history of chronic lung disease and in whom the PEFR is near the predicted normal value. Acute bronchitis usually does not produce hypoxemia in an otherwise healthy person.
On occasion, purulent bronchitis can lead to mucus plugging and shunt, as demonstrated by a small series of patients studied with V/Q scanning.86
When mucus plugging is severe, treatment with a b2
-agonist agent can transiently worsen oxygen saturation. This is because the b2
-agonist produces pulmonary vasodilation in areas of non-ventilated lung, thus increasing shunt. However, patients may symptomatically feel better as the work of breathing is diminished.Myocardial Ischemia
Physicians have long recognized the syndrome of painless dyspnea due to myocardial ischemia. It has even been termed "blockpnea."87
Painless dyspnea often precedes angina in patients with significant coronary artery disease. In one study of British men with moderate-to-severe painless dyspnea, nearly 30% developed coronary artery disease within five years.88
The presumed mechanism for this ischemic dyspnea is impaired left ventricular contraction, diastolic dysfunction, and reduced lung compliance. These findings may underscore the importance of provocative cardiac testing in patients at risk for coronary artery disease who experience unexplained dyspnea.Pregnancy
Pregnancy certainly complicates the evaluation of dyspnea. Sixty to seventy percent of healthy women experience physiological dyspnea during pregnancy.89
However, pregnancy is a risk factor for two serious causes of dyspnea?eclampsia and PE. Pulmonary embolism is one of the leading causes of pregnancyrelated mortality and is responsible for 15% of all maternal deaths.83,90,91
Several mechanisms may cause physiologic dyspnea, including postural-dependent alterations in lung blood flow and increased sensitivity to CO2
However, dyspnea greater than 6 out of 10 on the Borg scale indicates a significant pathological process.15
The emergency physician must not overlook the diagnosis of PE in pregnancy. Fears of harm to the fetus from a ventilation-perfusion scan are misplaced. Dangers of untreated PE to both mother and fetus far outweigh the risks of radiation from either a V/Q scan or angiogram. 92,93
While consultation with an obstetrician is not inappropriate, emergency physicians must order the necessary tests if they suspect PE. The examining physician has a far better understanding of the need for such tests than a consultant called at home.
Fetal exposures can be reduced by placing a lead apron over the uterus during the chest x-ray and performing a half-dose perfusion scan without the ventilation component.94,95
A normal perfusion scan will rule out the diagnosis of PE.
Congestive Heart Failure
The emergency physician can usually determine the presence of heart failure based upon the clinical examination and a few simple tests. Physician judgment is quite accurate in excluding the diagnosis. If the emergency physician does not believe the patient clinically has congestive heart failure, and the chest radiograph and ECG are both normal, then the dyspnea is not due to CHF.30
A history of congestive heart failure does not mean the current episode of dyspnea is due to an exacerbation of failure. PE is a significant cause of mortality in patients with CHF. One multi-center study shows that a history of congestive heart failure doubled the death rate from PE.96
Pulmonary embolism in patients with a history of congestive heart failure may be indistinguishable from an exacerbation of CHF.18,75
Historical factors may help distinguish the two conditions; patients who stop taking their cardiac medications and those who complain of progressive orthopnea and weight gain are more likely to have failure. The patient with acute dyspnea remains at risk of embolism.
Unfortunately, no specific bedside tests can reliably distinguish a patient with acute PE and prior CHF from a patient with a simple exacerbation of congestive heart failure. The chest radiograph is helpful, as radiographic evidence of lung edema is 95% sensitive for failure.30
Isolated PE is unlikely to produce such a finding.74,83
Liberal use of V/Q scans, echocardiography, or helical CT may be necessary in dyspneic patients with a history of CHF and relatively normal chest films.97
Transthoracic echocardiography may distinguish congestive heart failure from PE. Finally, the PEFR can help differentiate CHF from obstructive airway disease as a cause of dyspnea.35Psychogenic Dyspnea
Psychogenic dyspnea is synonymous with psychogenic hyperventilation. It is seen in young people with no identifiable organic cause. The etiology is multifactorial and may overlap with panic disorder. Both disorders may be related to heightened sensitivity to arterial PCO2
Panic attacks usually come without warning and are not necessarily precipitated by a stressful situation. Patients experiencing a panic attack may complain of a lump in their throat (globus hystericus) or that their clothes or undergarments are too tight. There are several characteristic types of panic attacks. The unexpected panic attack occurs spontaneously, without a situational trigger. The situational-bound panic attack occurs upon exposure to a frightening stimulus (seeing a snake, dog, or other frightening trigger).99
The diagnosis of psychogenic dyspnea in the ED should be a diagnosis of exclusion. It is best reserved for young, healthy patients with a history of previous attacks. The diagnosis of a new-onset panic attack or hyperventilation syndrome in an older adult invites tragedy?and litigation. (See also the "Ten Excuses That Don't Work In Court".)
When discharging the patient with presumed psychogenic dyspnea, avoid premature closure in diagnosis. The ED diagnosis may reflect "dyspnea, etiology unknown," and the differential diagnosis may include psychogenic dyspnea. Patients with psychogenic dyspnea may respond to anxiolytics.100
The deconditioning syndrome occurs in patients with exertional dyspnea without organic etiology. patients are usually greater than 30% over the ideal body weight for height and have a sedentary lifestyle. Psychogenic dyspnea may account for 32% of unexplained shortness of breath, while deconditioning is responsible for another 28%.10
Among young ambulatory patients with a normal evaluation, as many as half of the subjects may have psychogenic dyspnea or deconditioning syndrome.10-12,100
Such patients are not expected to have a low pulse oximetry, abnormal chest x-ray, or abnormal vital signs. Deconditioning may improve after exercise and weight loss protocol (an endpoint difficult to achieve during an ED visit).