The history, physical examination, and chest film will accurately predict the cause of dyspnea in about twothirds of patients.11
These three basic investigations will frequently determine the need for
other studies. The Clinical Pathway "Management Of Unexplained Dyspnea" summarizes the approach to patients with dyspnea.History
will provide important clues to the diagnosis and the need for further
investigation. Determine the patient's risk for serious disease. Of
particular importance is the patient's age, past medical conditions,
and associated symptoms.Timing: Acuity And Duration
the onset immediate or gradual, and is the dyspnea acute, chronic, or
recurring? The duration of symptoms before presentation provides
important information. Patients with symptoms for longer than two weeks
are more likely to have mild congestive failure, anemia, pulmonary
hypertension, chronic lung disease, or recurrent pulmonary embolism.
events surrounding acute dyspnea may be revealing. Was the patient
eating (suggesting the presence of a foreign body or allergic
reaction)? Was the patient SCUBA diving (suggesting that the patient
has an air embolism or pneumothorax)?The Patient's Use Of Descriptors
language a patient uses to describe dyspnea varies with age, ethnicity,
and severity of the underlying etiology.2,15
Patients may use terms
such as "shortness of breath," "shortness of wind," "breathlessness,"
"trouble breathing," "suffocating," "chest tightness," "breathing at
the top of my lungs," or "heavy breathing." Normal volunteers who are
subjected to various experimental causes of dyspnea (ranging from low
oxygen to increased work of breathing) can distinguish the cause of
dyspnea through their choice of descriptors.2
the same diagnoses tend to use similar language to describe their
Thus, it is possible that the patient's words can help to
target his or her particular pathophysiology.(See Table 2
for some examples.)
Ask patients to grade the severity of the dyspnea. The modified Borg scale is employed by many pulmonary clinics. (See Table 3
Like the numerical scale used to grade the severity of chest pain, the
Borg scale measures the severity of dyspnea from 0 to 10. Zero
represents no shortness of breath, while a 10 signifies severe,
oppressive symptoms. Simon et al showed that acute asthma, COPD, and
CHF all produce severe dyspnea (7 out of 10), whereas dyspnea
associated with normal pregnancy, neuromuscular causes, or PE was
described as moderate by most patients (5 out of 10).15
(Note that a potentially lethal cause of dyspnea caused only moderate shortness of breath!)Associated Symptoms
The associated symptoms provide focus to the emergency evaluation, and the presence of chest pain is of special concern.15
The location and quality of the pain may help narrow the differential
diagnosis. Cardiac pain tends to be more substernal and constant, while
the pain of pneumonia and pulmonary embolism is usually more peripheral
and tends to increase with respirations. Interestingly, in the PIOPED
(Prospective Investigation of Pulmonary Embolism Diagnosis) study, no
patient with PE had radiation of pain to the arms.16
Cough is nonspecific and may represent asthma, pneumonia, PE, heart failure, or bronchitis. Fever is also nonspecific and may occur with infection or PE. However, patients with PE rarely have a fever greater than 102?F.16
While dyspnea with exertion often suggests congestive failure, it may occur with reactive airway disease, PE, pneumonia, anemia, or physical deconditioning. Orthopnea occurs with both cardiac and pulmonary causes of dyspnea.Past Medical History
Past medical history is often illuminating. Ask the patient, "Has this ever happened to you before?" The patient who mutely responds with an empty canister of albuterol makes an eloquent statement. Always ask regarding a prior history of PE or deep venous thrombosis (DVT). A prior history of thromboembolic disease may mandate extensive testing for PE. Some patients, however, mistake a prior evaluation for PE to represent a diagnosis of PE. Others believe having a varicose vein or a hematoma on the leg represents a "blood clot." If patients report prior PE or DVT, determine whether they were
ever on warfarin.
Ascertain whether the patient has taken a new drug or is compliant with chronic medications. A new prescription for beta-blockers or calcium-channel blockers can precipitate congestive heart failure, while aspirin abuse may cause metabolic acidosis. The use of birth control pills or other estrogen products increases the risk of PE in women who smoke.Social History
The social history is rarely emphasized in emergency practice; however, this aspect of the interview is important in the patient with dyspnea. For instance, a patient who does not smoke cigarettes is very unlikely to have COPD.11
HIV risk factors become important in the patient with possible pneumonia.Physical Examination
The astute emergency physician can identify the patient in respiratory distress from across the room. Unless moribund, the patient is anxious and is usually sitting bolt upright, employing the neck and chest muscles to assist in ventilation. He or she may be unable to speak or only capable of gasping short phrases. The skin is often dusky and diaphoretic. Fortunately, few patients present with such drama. However, with attention to various aspects of the physical examination, the emergency physician can frequently detect the cause of dyspnea.Vital Signs
Vital signs are crucial in the evaluation of the dyspneic patient. Hypotension and dyspnea are an ominous combination that may be due to a variety of etiologies?all bad. Eight percent of patients with PE may present in shock.16
Other considerations include cardiac etiologies, tension pneumothorax, occult hemorrhage, and metabolic disorders.
In patients with possible heart failure, consider measuring the proportional pulse pressure. The proportional pulse pressure is calculated using the following formula: (systolic pressure - diastolic pressure)/systolic pressure. A ratio of less than 0.25 predicts left ventricular systolic dysfunction.17
Tachycardia is generally a nonspecific finding, but persistent tachycardia requires explanation and often
Measurement of the respiratory rate deserves care. A normal respiratory rate ranges from 15-24 breaths per minute in the healthy adult. Patients on the lower end of normal are unlikely to have PE, as fewer than 15% of patients with PE have respiratory rates less than 20 breaths per minute.16,18
When measuring the respiratory rate, evaluate the patient during at least 30 seconds of quiet observation. In the histrionic patient, respirations counted surreptitiously from outside the room may be helpful.Head And Neck
Look in the mouth of patients with unexplained dyspnea. The presence of oral thrush will quickly narrow the differential diagnosis. Dyspnea on exertion is a common complaint of patients with Pneumocystis carinii pneumonia (PCP).
Evaluation of the neck veins can also be useful. Jugular venous distention is seen with right heart failure. Kussmaul's sign, a paradoxical increase in the neck veins with inspiration, occurs with pericardial tamponade, PE, pneumothorax, and right ventricular infarction.
Stridor, as opposed to wheezing, is likely to represent upper airway obstruction.Pulmonary Exam
General. Evaluate the duration of the inspiratory and expiratory phases of respiration. A prolonged expiratory phase (greater than twice the inspiratory phase) suggests obstructive lung disease. Listen to this patient's speech. Does he or she need to stop during each sentence to gasp for air?Inspection
. Look for the previously mentioned signs of respiratory distress, such as intercostal retractions, accessory muscle use, and nasal flaring. Patients with airway obstruction may demonstrate paradoxical sternal retractions with inspiration, a finding more prominent in children.Palpation
. Palpation is rarely helpful in the absence of trauma. However, a patient with spontaneous pneumothorax may occasionally have subcutaneous air palpable at the root of the neck.Percussion
. Traditionally, percussion is used to detect effusions, infiltrates, and pneumothorax. The traditional technique of tapping with a finger or hammer on the chest is employed with spotty frequency and success in the ED. However, a variation of this technique, termed the "auscultatory-percussion" test, is both useful and generally unknown to the emergency physician.
To perform this test, tap on the second thoracic vertebra and use a stethoscope to compare the percussion notes on each side of the anterior and lateral chest. Then tap on the sternum while listening to each side of the posterior chest. If the percussion note on one side is different in intensity or character from its "mirror image" sound on the other, the test is positive, and the patient is likely to have an abnormality on chest radiography. Some studies suggest that this test is more sensitive than simple auscultation for a variety of pulmonary diseases.19,20
Other studies have not shown such positive results.Auscultation.
This aspect of the physical examination will likely direct further management. A unilateral decrease in breath sounds should raise consideration for a spontaneous pneumothorax, atelectasis, pleural effusion, or pneumonia.
Auscultate the lungs for wheezing and rales. While these are signs of pathology, they are very nonspecific. All that wheezes is not asthma; wheezing may occur with foreign bodies, pneumonia, congestive heart failure, or PE. Rales may occur with pneumonia, interstitial lung disease, COPD, or CHF. In CHF, rales are neither sensitive (13%) nor specific predictors of systolic dysfunction. However, the absence of rales eliminates 98% of patients with interstitial lung disease.11
Rales are common in PE, and one-half of such patients with angiographically confirmed PE may demonstrate rales on physical exams.18
Some believe that the traditional chest physical examination alone is not sufficiently accurate to confirm
or exclude the diagnosis of pneumonia. In one study, the most valuable examination maneuvers in detecting pneumonia were unilateral rales and rales in the lateral decubitus position.21Cardiac Exam
Auscultate the heart. An S3 gallop is a significant finding that suggests congestive heart failure. Murmurs may also be revealing. Important murmurs include the diastolic murmur (and opening snap) of mitral valve stenosis and the systolic murmur of aortic stenosis. Rupture of a papillary muscle may result in acute mitral regurgitation and a loud systolic murmur radiating to the axilla. An accentuated component of the second heart sound may occur in more than half of the patients with angiographically proven PE.18
(Although it would be an impressive clinician indeed who could make this diagnosis simply upon listening to the heart!)Extremity Exam
Examine the extremities for evidence of cyanosis and edema. While peripheral edema is common in patients with right-sided or biventricular failure, it is usually absent in patients with acute left ventricular dysfunction. Look for stigmata of chronic hypoxia such as clubbing. Dyspneic patients with unilateral leg swelling, calf tenderness, or distended superficial veins are likely to have PE.22
However, most patients with PE do not have any extremity signs or symptoms.
The skin exam is normal in most patients with dyspnea. Cyanosis is rare and may be caused by either severe methemoglobinemia or profound hypoxemia. The anemic patient may not be cyanotic despite severe hypoxemia, as this requires at least 5 grams of unsaturated hemoglobin. 23
Diaphoresis denotes sympathetic overdrive and is common with CHF and ischemic disease. Its presence in an asthmatic patient is worrisome.Physical Examination Maneuvers
There are two diagnostic maneuvers that are useful in patients who complain of shortness of breath; both target the individual at risk for cardiac dysfunction. The simplest maneuver is hepatojugular reflux. In patients with heart failure, pressing on the liver should result in distention of the neck veins.24
The second test involves a maneuver similar to that used in measuring the pulsus paradoxus.25
The patient must grunt (Valsalva) while a blood pressure cuff is inflated 15 mmHg above their systolic pressure. In a patient with normal cardiac function, the physician will hear the patient's heartbeat immediately after release of the cuff. In the presence of systolic dysfunction, return of the auscultated heartbeat is delayed after cuff deflation, or else it persists throughout cuff inflation and deflation.
The most useful diagnostic tests in the evaluation of dyspnea are simple, widely available, and relatively
inexpensive. These are the pulse oximetry and the chest x-ray.Pulse Oximetry
Some consider oxygen saturation as the "fifth vital sign," and its role in emergency medicine seems boundless. In some large EDs, all patients who present to triage receive a screening pulse oximetry.
Pulse oximetry is a valuable tool in evaluation of dyspnea; it is rapid, generally reliable, and accurate. It is considerably more sensitive to hypoxia than the physician's clinical impression.26
Healthy individuals should have an oxygen saturation of at least 95% or greater. Many smokers, elderly
patients, and obese patients maintain oxygen saturations between 92% and 95%. Lower levels in a dyspneic patient require an explanation and often further diagnostic testing if the etiology of hypoxia remains in doubt. For select patients, an arterial blood gas (ABG) may provide additional information.
Emergency physicians can use pulse oximetry to measure oxygen saturation before and after
having a patient walk or exercise. A drop in oxegen saturation with exercise is characteristic of Pneumocystis carinii pneumonia.27
Pulse oximetry may also aid in treatment decisions. Patients with low levels require supplemental oxygen (although those with a significant shunt may not show improvement). A pulse oximetry reading of less than 90% suggests the need for admission in a patient with pneumonia, regardless of other factors.28Limitations Of Pulse Oximetry
. Despite the usefulness of pulse oximetry, the emergency physician must remain aware of its limitations. Pulse oximetry may be unobtainable in patients with shock, hypothermia, or severe vasoconstriction. It cannot detect abnormal hemoglobins that occur in patients with carbon monoxide toxicity or in those with methemoglobin. Pulse oximetry gives a false reading in cases of optical shunt. With sensor misplacement, the oximeter's light may not pass completely through the patient's finger, but may shine directly into the light receiver, creating an optical shunt. In this case, the monitor will not show a normal waveform.
Pulse oximetry measures oxygen saturation; it does not evaluate ventilation. Pulse oximetry cannot detect hypercarbia and impending respiratory failure, especially if the patient is given given supplemental oxygen. Do not exclude PE based on a normal pulse oximetry value. Oxygen saturation may be normal in a quarter of patients with PE.16Chest Radiography
Chest radiography is a high-yield study in many patients with unexplained dyspnea. An anterior posterior (AP) or posterior anterior (PA) film plus a lateral projection provides a better view of chest structures than the portable AP study. In a prospective study of 221 ambulatory patients with cardiorespiratory complaints, chest x-ray demonstrated significant new abnormalities in more than one-third of patients.29
The most common abnormality was pulmonary infiltrate (18%).
Chest films are useful to determine the cause of unexplained dyspnea and the severity of suspected
etiologies. In pneumonia, they can detect high-risk findings such as pulmonary effusions, multi-lobar
disease, and cavitation. A normal film essentially rules out clinically significant pneumothorax. Chest radiography is invaluable in the diagnosis of congestive heart failure. Chest radiography combined with clinical assessment is 85% sensitive and 92% specific in detecting systolic dysfunction compared to echocardiography.30Limitations Of Chest Radiography
. Findings on chest films may be new or old, and without prior films,
this distinction may be impossible to make. The film may lag behind the clinical examination in many acute conditions, especially in adult respiratory distress syndrome (ARDS). While the chest x-ray provides important clues for PE, it may also obscure the diagnosis. The only time the chest film can exclude PE is when it demonstrates an incontrovertible alternative diagnosis (e.g., a pneumothorax). (Even then, it is possible for a truly unfortunate patient to have both diagnoses.) Significantly, it is impossible for a radiologist or emergency physician to distinguish PE from pneumonia on a chest film.18
A patient with a history of asthma or COPD does not routinely need a chest film. Chest x-rays may be necessary in patients who fail ED therapy and in those for whom a competing diagnosis is likely, such as concurrent pneumonia or CHF.31,32Electrocardiography
Electrocardiography is particularly helpful in dyspneic patients with risk of cardiac disease. Myocardial ischemia is an important cause of painless dyspnea. Elderly patients and those with diabetes are likely to have atypical presentations of cardiac ischemia, especially shortness of breath.33
The electrocardiogram (ECG) may be positive in other causes of cardiac dyspnea, such as CHF, pericardial effusion, pulmonary hypertension, or rhythm disturbances.
Which patients with dyspnea need an ECG? Order an ECG for unexplained dyspnea in patients at risk for cardiac conditions. Although this population is not strictly defined, it may include men over age 35, postmenopausal women, and patients with ischemic risk factors such as hypertension, diabetes, family history of myocardial infarction, and especially those with prior cardiac disease. Dyspnea related to cardiac ischemia might be painless or can be accompanied by discomfort in the chest, jaw, neck, back, arms, or upper abdomen.
Evaluate the 12-lead ECG for evidence of myocardial ischemia, rate or rhythm disturbance, and evidence of hypertrophy. Atrial fibrillation can produce dyspnea by reducing cardiac output.
Left ventricular hypertrophy combined with elevations in the diastolic pressure suggests the possibility of left ventricular dysfunction. Electrocardiography improves the specificity of the physical exam in patients suspected of congestive heart failure. Clinical assessment alone is 41% sensitive for CHF, compared to 69% when ECG is incorporated. A normal ECG makes heart failure an unlikely diagnosis in the breathless patient, as a normal ECG has a 98% negative predictive value for left ventricular systolic dysfunction.18
Electrocardiography is rarely helpful in the diagnosis of PE. However, one study showed that symmetric Twave inversion in lead V1-4 was 85% sensitive and 81% specific for PE?but most of these patients had massive emboli.34
The famous S1 Q3 T3 pattern (often used to harass physicians in training) was only 54% sensitive for PE. In this study, no patients with submassive PE had sinus tachycardia.Peak Expiratory Flow Rates
Peak expiratory flow rates (PEFR) may be helpful in the emergency evaluation of the dyspneic patient. The following are several ccirumstances in which PEFRs are used in the ED:
- To Determine The Cause Of Dyspnea
Peak expiratory flow may help distinguish dyspnea produced by chronic lung disease from cardiogenic dyspnea. McNamara and Cionni prospectively studied 56 dyspneic patients and found that peak expiratory flows in patients with cardiac dyspnea were twice that of patients with obstructive airway disease (224 L/min vs 108 L/min).35,36
Significant improvements in peak flow after bronchodilator therapy provide strong presumptive evidence that reactive airway disease is the source of dyspnea. Conversely, a near normal peak flow suggests that airway restriction is not the cause of dyspnea and may redirect the evaluation toward cardiac or other etiologies.
- To Limit The Need For ABGs In COPD And Asthma
PEFR rates can eliminate or decrease the need for arterial blood gases in the patient with COPD or asthma. In an ED study, no patient with a PEFR greater than or equal to 25% predicted had a PaCO2 greater than 45 mmHg or pH less than 7.35.37
- To Direct ED Management Of The Patient With Asthma
The National Asthma Guidelines suggest obtaining a measurement of peak flow in all but the moribund patient, before and after each bronchodilator treatment in the ED. This policy was based on consensus and not upon clinical studies. In reality, this guideline conflicts with a variety of evidence. While PEFRs are useful in home management, their routine use in the ED to guide management remains in question.
Peak flows depend upon patient effort. A poor effort results in a poor score?and if the guidelines are strictly followed, an unnecessary admission. Some studies show that PEFRs do not correlate with the need for hospital admission.38 A recent welldesigned multi-center trial showed that PEFRs do not predict relapse in patients discharged from the ED.39
Even in patients with COPD, peak flow does not correlate with severity of dyspnea. The patient may experience a good response to bronchodilator treatment despite insignificant changes in PEFR.Ventilation Perfusion Scans
The ventilation perfusion (V/Q) lung scan is traditionally used to screen for PE.40
While a completely normal perfusion scan nearly eliminates this diagnosis, such a finding is rare. Most scans are indeterminate.
The V/Q scan has numerous limitations, and the terminology is misleading. A low-probability scan is a misnomer?angiography will demonstrate PE in as many as 12% of these patients.41
As many as 40% of patients with high pretest probablility and "low-probability scans" may have pulmonary emboli.42,43
When an emergency physician strongly suspects PE on clinical grounds, he or she should order additional tests for PE?despite a low-probability scan.
To effectively use the V/Q scan, the emergency physician must determine the clinical likelihood for PE before receiving the radiologist's reading. (See Table 4
.) The pretest probability of PE remains a gestalt, and no validated scoring system yet exists.
If the clinical suspicion is discordant with the reading (low suspicion but high-probability scan, or high suspicion but low-probability scan), additional testing is needed. Any patient with a moderate probability or indeterminate scan requires additional testing.
Arterial Blood Gases
Arterial blood gases (ABGs) are not routinely necessary for the dyspneic patient. In the COPD or asthmatic patient, a peak flow of 25% or greater than predicted may obviate the need for ABG. In many patients, pulse oximetry alone may be sufficient.
ABGs are useful in patients who have altered mental status and in those suspected of acidosis. Other indications include persistent hyperventilation, patients who are critically ill, and those with impending ventilatory failure.
In patients with unexplained dyspnea, the arterial alveolar gradient (A-a DO2
) provides significant information. This number represents the gap between the partial pressure of oxygen in the alveolus and the partial pressure of oxygen in the blood. The wider the A-a DO2
gradient, the more significant the physiologic impairment. There is both a rigorous and a simple way to calculate the A-a DO2
gradient. (See Table 5
for the fancy way.) For quick determination of the A-a DO2
gradient at sea level, use the formula 150 minus 1.25 times PCO2
= 150 - 1.25 x PCO2
The A-a DO2
gradient normally increases with age. To adjust for age, use the following formula to give the expected age-appropriate gradient: patient age divided by four, plus four (adjusted normal for age = age/4 + 4).44
Thus, a 40-year-old smoker should have an A-a DO2
gradient of 14 mmHg.
The baseline A-a DO2
gradient increases in smokers and those with intrinsic lung disease such as COPD. It can only be determined accurately in a patient who is breathing room air, as the FIO2
on supplemental oxygen can only be estimated.Hemoglobin And Hematocrit
Determine the hemoglobin concentration in patients at risk for anemia. Such patients include those with melanotic stool, heavy vaginal bleeding, recent chemotherapy, history of AIDS, or recent trauma or surgery. Pale conjunctiva may suggest this diagnosis on physical examination. A fingerstick hemoglobin will suffice for most patients in whom anemia is a consideration.Additional Testing
Additional tests may provide important information in patients in whom standard studies are unrevealing. Most of these additional tests focus on the heart and lungs. Patients with persistent tachycardia and dyspnea may need evaluation for thyrotoxicosis.9
When the emergency physician continues to suspect cardiac disease due to a combination of risk factors or clinical exam, consider exercise testing or myocardial perfusion imaging.10,11
Echocardiography is becoming more accessible in emergency care. Transthoracic echo is very sensitive to pericardial effusion, even in the hands of a novice. Other findings such as valvular dysfunction and wall motion abnormalities require extensive training and sophisticated equipment.
Most patients with congestive failure can be diagnosed on clinical grounds coupled with chest radiography and ECG. Emergent echocardiography may help distinguish patients in whom the diagnosis of congestive failure vs. PE remains unclear.
Patients with congestive failure should have stigmata of left ventricular dysfunction, while those with significant PE may have right ventricular hypokinesis, dilatation of the right ventricle, or tricuspid regurgitation. Crawford and Hendry reported that clinical impression coupled with radiological findings was only 74% sensitive and 54% specific for systolic dysfunction in 61 patients with suspected heart failure.45
Echocardiography in these same patients led to important changes in management. They discovered three cases of cor pulmonale and 10 cases of valvular or pericardial disease.
Among patients with suspected PE, overall sensitivity for trans-thoracic echo in four prospective studies (n=317) was 80%, while specificity was 85%.46-49
In these studies, echocardiography assisted in the distinction between PE and congestive heart failure.Pulmonary Tests
Pulmonologists may perform the methacholine challenge test in patients suspected of having atypical presentations of asthma. Other sophisticated pulmonary tests include the single-breath carbon monoxide diffusion test for interstitial lung disease.The Cutting Edge: New Modalities To Screen For PE
Surely, no topic evokes such spirited debate as how to screen for PE. Every test seems to have as many drawbacks as advantages. Fortunately, diagnostic options available to the emergency physician are expanding.Contrast-Enhanced Spiral (Or Helical) CT
The helical CT is able to image pulmonary vasculature as well as other thoracic structures. There are nine studies that use pulmonary angiography as a gold standard (n = 371),50-58
and four that use other criteria to diagnose PE (n = 611).59-63
The pooled sensitivity was 86% and the specificity was 93% for PE in these studies.
In the near future, refinements in helical CT may make computer tomography a test of choice for PE. However, at the current time, helical CT is most accurate for large central emboli and is insensitive for small peripheral clots.
The emergency physician should order helical CT for patients with suspected emboli who are likely to have non-diagnostic V/Q scans. This includes those with COPD, heavy cigarette use, sarcoidosis, pulmonary fibrosis, or those with an infiltrate on chest radiograph.64
Patients with an infiltrate on chest x-ray will have a non-diagnostic V/Q scan 82% of the time.64
A V/Q scan is likely to waste time and money in a pateint with focal consolidation.D-Dimer Assay
D-dimer is a product of blood clot breakdown that rises in patients with thromboembolism. However, it is also elevated in patients with infection and those with inflammatory or neoplastic conditions. There are multiple commercial assays available for D-dimer, and four may be performed in less than one hour?some at the bedside.
The tests include:
- The erythrocyte agglutination assay (SimpliRED? [Agen Biomedical, Ltd., Brisbane, Australia]);
- The turbidimetric assay (Liatest [Stago, Asnieres, France] and Turbiquant [Behringwerke, Marburg, Germany]);
- The rapid ELISA test (VIDAS [Biomerieux, France] and Instant IA [Stago, Asnieres, France]); and
- The immunofiltration assay (NycoCard D-dimer [NycoMed Pharma AS, Norway]).
Most of these assays are positive when the D-dimer concentration is more than 500 ng/mL.
The SimpliRED assay is the most extensively studied and probably most user-friendly test for ED evaluation.65
Five studies of the SimpliRED assay (n=1376) show a pooled average sensitivity of 90% and specificity of 60% for PE.65,67,69,102-104
The turbidimetric assays have also shown good test performance in three studies (n=684), with a sensitivity of 98% and a specificity of 43%.66-68
In one study, the combination of any two of the following?a normal SimpliRED D-dimer, a PO2
of 80 mmHg or more, or a respiratory rate less than 20?was unlikely to miss a pulmonary embolism.69
No patient with a normal SimpliRED test, a PO2
of 80 mmHg or greater, and a respiratory rate less than 20 had a PE in this trial.
The new-generation D-dimer assays are useful adjuncts to standard clinical criteria. They are probably best suited to the outpatient setting, where there may be fewer false-positives due to the lack of comorbid disease. In low-risk patients, a negative D-dimer assay can significantly lower the probability of PE. A negative D-dimer in conjunction with a low clinical probability provides a negative predictive value of 97%.65
Do not use the latex agglutination assays, as their sensitivity is poor (71%).67,70-72