Akin to the ultrasound first for appendicitis protocol currently in use, the authors of a recently published study in CHEST propose using ultrasound before CTPA in patients where the diagnosis of pulmonary embolism is being considered.
Their protocol consisted of bedside thoracic and lower extremity ultrasounds to identify either a confirmatory DVT or an alternative diagnosis that would account for the patient’s current presentation. In both the ED and inpatient settings, ICU physicians evaluated this protocol’s performance in 100 patients. The 54 patients who were determined, due to an alternative diagnosis found on ultrasound, not to require further testing, none of them were found to have a pulmonary embolism on confirmatory CT. Of the remaining 40 patients (42%) whose ultrasound revealed no convincing alternative diagnosis or lower extremity DVTs, 12 were found to have pulmonary embolisms on their confirmatory CTPA. The authors conclude that though further studies are needed, an ultrasound first strategy will reduce the number of CTs obtained to rule out pulmonary embolism.
Though I am not opposed to the utilization of ultrasound as a bedside tool, using it to rule out pulmonary embolisms is a flawed paradigm. The proposed protocol is not one which rules out PE, it in fact does just the opposite. This protocol takes advantage of the high specificity of ultrasound for the diagnosis of pneumonia, pulmonary edema, and DVT. It employs the strategy of ruling in an alternative diagnosis or a lower extremity DVT. If no convincing diagnosis is discovered the patient will then move on to the more traditional rule out strategy of CTPA. This study essentially uses bedside ultrasound to address the two most heavily weighted criteria on the Well’s Score, “an alternative diagnosis that is less likely than pulmonary embolism” and “signs and symptoms of deep venous thrombosis”. In no way is this protocol fatally flawed. It has the potential to add a great deal to clinical decision making. Unfortunately it does not address the more serious epidemic in the current management of pulmonary embolisms. That is the egregious over-testing and subsequent over-diagnosis of pulmonary embolism in the ultra low risk patient.
“Ultrasound Assessment of Pulmonary Embolism in Patients Receiving Computerized Tomography Pulmonary Angiography”
journal.publications.chestnet.org/article.aspx?articleid=1763837
journal.publications.chestnet.org/article.aspx?articleid=1763837
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I agree with your conclusions, though I would make one additional consideration to address the relevance of this study.
There is one main aspect that draws my attention as a ultrasound freak: the chest US protocol itself.
Apparently the investigators have been using the BLUE protocol as per Lichtenstein. If this is true, the diagnostic yield of chest US is going to be low. The patients included in the study mainly presents with a non severe clinical picture (10% hypoxia, none with hypotension). The BLUE protocol works greatly on critical ill patients in the ICU, but has a much lower sensitivity when used on patients not in respiratory failure. It does not evaluate the posterior surface of the lungs. You will miss a lot of things, particularly pneumonia, if you are not scanning the whole chest. So I'm curious to know which findings did the CT revealed in the group with a negative integrated sonographic protocol. My two cents are that the proportion of patients with an alternative diagnosis would have been much higher if a more comprehensive thoracic approach would have been used. Will have to see the full article.
I agree with your conclusions, though I would make one additional consideration to address the relevance of this study.
There is one main aspect that draws my attention as a ultrasound freak: the chest US protocol itself.
Apparently the investigators have been using the BLUE protocol as per Lichtenstein. If this is true, the diagnostic yield of chest US is going to be low. The patients included in the study mainly presents with a non severe clinical picture (10% hypoxia, none with hypotension). The BLUE protocol works greatly on critical ill patients in the ICU, but has a much lower sensitivity when used on patients not in respiratory failure. It does not evaluate the posterior surface of the lungs. You will miss a lot of things, particularly pneumonia, if you are not scanning the whole chest. So I'm curious to know which findings did the CT revealed in the group with a negative integrated sonographic protocol. My two cents are that the proportion of patients with an alternative diagnosis would have been much higher if a more comprehensive thoracic approach would have been used. Will have to see the full article.
Great post, thank you.
This study addresses the extremely common diagnostic error of falling into the “rule out PE” trap.
When a patient presents to the ED with dyspnea, the right question is “why is this patient dyspneic.” The wrong question is “does this patient have a PE or not.” All too often, clinicians become overly focused on the issue of PE causing tunnel vision. Too many patients get CT pulmonary angiograms prior to chest radiograph, when a chest X-ray would have easily revealed the etiology of the patient’s dyspnea.
I think bedside sonography is powerful largely because it re-focuses the clinician on the important question: “what is wrong with this patient,” rather than the diagnostic trap of “rule-out PE.”
Josh
Great post, thank you.
This study addresses the extremely common diagnostic error of falling into the “rule out PE” trap.
When a patient presents to the ED with dyspnea, the right question is “why is this patient dyspneic.” The wrong question is “does this patient have a PE or not.” All too often, clinicians become overly focused on the issue of PE causing tunnel vision. Too many patients get CT pulmonary angiograms prior to chest radiograph, when a chest X-ray would have easily revealed the etiology of the patient’s dyspnea.
I think bedside sonography is powerful largely because it re-focuses the clinician on the important question: “what is wrong with this patient,” rather than the diagnostic trap of “rule-out PE.”
Josh
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I completely agree. I think ultrasound provides most of its diagnostic utility in the undifferentiated dyspnic patient. Though using this protocol, in the way it was intended, may reduce the amount of CTPAs by a small amount secondary to alternative diagnosis surely most of the ultra low risk patients will have to continue down the pathway to CTPA. Like any such protocol if we expand the population it may even increase testing. Very interesting concept nonetheless.
Thanks so much for your input, I really appreciate the support!!
I completely agree. I think ultrasound provides most of its diagnostic utility in the undifferentiated dyspnic patient. Though using this protocol, in the way it was intended, may reduce the amount of CTPAs by a small amount secondary to alternative diagnosis surely most of the ultra low risk patients will have to continue down the pathway to CTPA. Like any such protocol if we expand the population it may even increase testing. Very interesting concept nonetheless.
Thanks so much for your input, I really appreciate the support!!
Thanks Mattia for your insight. It is interesting that the BLUE Protocol is in someways like the FAST exam where it provides its most utility utility in the unstable patient. I have no doubt if they expanded their protocol to include the posterior surface of the thorax they would have found more alternative diagnoses. I do wonder if at times ultrasound may be too sensitive. Is it possible that some cases of US+ pneumonia are too subtle for X-ray and would traditionally be considered bronchitis, not require antibiotics? Are we identifying a subset of CXR negative pneumonias that will benefit from antibiotics or is this another case of dilution of disease severity secondary to our increased medical technology? What do you think?
Thanks again, your comments were very helpful!!
Thanks Mattia for your insight. It is interesting that the BLUE Protocol is in someways like the FAST exam where it provides its most utility utility in the unstable patient. I have no doubt if they expanded their protocol to include the posterior surface of the thorax they would have found more alternative diagnoses. I do wonder if at times ultrasound may be too sensitive. Is it possible that some cases of US+ pneumonia are too subtle for X-ray and would traditionally be considered bronchitis, not require antibiotics? Are we identifying a subset of CXR negative pneumonias that will benefit from antibiotics or is this another case of dilution of disease severity secondary to our increased medical technology? What do you think?
Thanks again, your comments were very helpful!!
Ultrasound can serve to remove some anchoring bias that you can develop in the work up of the acutely dyspneic patient as shown by the alternative diagnoses. However, I do agree that the thought process should be why do they have dyspnea and not do they have a PE. I tend to use ultrasound to rule in a diagnosis rather then rule out, in many studies the positive predictive value is great but the negative predictive value is much lower.
I don't have a problem with an ultrasound first approach but it has to be with the caveat that the ultrasound exam or profile should be done correctly and in a similar method to the study in question.
We may in fact be finding pneumonias that are less severe then what we would find with a CXR. As to whether these patients would do fine without antibiotic therapy or would the ones who bounce back in a day or two with a worsening condition I don't think we know. At least not yet.
Ultrasound can serve to remove some anchoring bias that you can develop in the work up of the acutely dyspneic patient as shown by the alternative diagnoses. However, I do agree that the thought process should be why do they have dyspnea and not do they have a PE. I tend to use ultrasound to rule in a diagnosis rather then rule out, in many studies the positive predictive value is great but the negative predictive value is much lower.
I don't have a problem with an ultrasound first approach but it has to be with the caveat that the ultrasound exam or profile should be done correctly and in a similar method to the study in question.
We may in fact be finding pneumonias that are less severe then what we would find with a CXR. As to whether these patients would do fine without antibiotic therapy or would the ones who bounce back in a day or two with a worsening condition I don't think we know. At least not yet.
I would love to see some work on CXR-, US+ pneumonias and how they respond to antibiotics. You are right they may very well be the subset of bronchitis we see that bounce back in a few days requiring antibiotics. On the other hand they may be so subtle they do fine without treatment.
I agree that ultrasound performs far better when used to rule in pathology than when used to rule out. It is interesting that its performance (FAST, BLUE, r/o appendicitis) is far more dependent on the severity of the disease in question than either CT or MRI. I'm not sure if this is a characteristic of the US itself or the fact that it is far more user dependent.
Thanks for your input!!
I would love to see some work on CXR-, US+ pneumonias and how they respond to antibiotics. You are right they may very well be the subset of bronchitis we see that bounce back in a few days requiring antibiotics. On the other hand they may be so subtle they do fine without treatment.
I agree that ultrasound performs far better when used to rule in pathology than when used to rule out. It is interesting that its performance (FAST, BLUE, r/o appendicitis) is far more dependent on the severity of the disease in question than either CT or MRI. I'm not sure if this is a characteristic of the US itself or the fact that it is far more user dependent.
Thanks for your input!!
I share your concerns. Despite being passionate about bedside ultrasound I make the effort to evaluate it as all other imperfect tests. I guess the real problem is that we don't really know its real diagnostic accuracy.
With the exception of pneumothorax, we don't have strong evidence to claim chest US will work always as well as in the hands of the experts, who actually produced most of the data. Furthermore we need to consider that the majority of the studies produced so far have several limitations and rarely compared results with gold standards.
It is indeed a very sensitive tool and this might be an issue.
To keep in line with your reasoning US will inevitably find more pneumonia than x-ray. As to whether these sonographic findings represent a distinct, self limiting, entity I don't know, but it could possibly be for some of them.
One last consideration: specificity. As the author of the paper mentioned in the discussion, peripheral pulmonary embolism might present with consolidations patterns. I'm not referring to the apparently specific wedge/polygonal/rounded hypoechoic lesions that have been described by Reissig and Mathis. Sometimes peripheral emboli cause discrete consolidations with bronchograms, focal interstitial syndrome or just effusion. Despite this is an infrequent occurrence it may lead to wrongly ruling out PE.
Don't get me wrong I really think beside ultrasound greatly improves our work as emergency physician. I firmly believe it will be common practice in the next future. As to what extent it will improve or substitute traditional diagnostic algorithms we still need to figure out.
Most probably ultrasound protocols need to be differentiated according to pretest probability to come to their best fruition, and, as obvious as it may sound, they are not substitutes of clinical judgment.
I share your concerns. Despite being passionate about bedside ultrasound I make the effort to evaluate it as all other imperfect tests. I guess the real problem is that we don't really know its real diagnostic accuracy.
With the exception of pneumothorax, we don't have strong evidence to claim chest US will work always as well as in the hands of the experts, who actually produced most of the data. Furthermore we need to consider that the majority of the studies produced so far have several limitations and rarely compared results with gold standards.
It is indeed a very sensitive tool and this might be an issue.
To keep in line with your reasoning US will inevitably find more pneumonia than x-ray. As to whether these sonographic findings represent a distinct, self limiting, entity I don't know, but it could possibly be for some of them.
One last consideration: specificity. As the author of the paper mentioned in the discussion, peripheral pulmonary embolism might present with consolidations patterns. I'm not referring to the apparently specific wedge/polygonal/rounded hypoechoic lesions that have been described by Reissig and Mathis. Sometimes peripheral emboli cause discrete consolidations with bronchograms, focal interstitial syndrome or just effusion. Despite this is an infrequent occurrence it may lead to wrongly ruling out PE.
Don't get me wrong I really think beside ultrasound greatly improves our work as emergency physician. I firmly believe it will be common practice in the next future. As to what extent it will improve or substitute traditional diagnostic algorithms we still need to figure out.
Most probably ultrasound protocols need to be differentiated according to pretest probability to come to their best fruition, and, as obvious as it may sound, they are not substitutes of clinical judgment.
Beautifully put! I completely agree. I'm sure US will serve us well if we are mindful in our application. Thanks again for all your input and support!!
Beautifully put! I completely agree. I'm sure US will serve us well if we are mindful in our application. Thanks again for all your input and support!!