I think we all can agree that the subtleties of the thoracic cavity go far beyond the diagnostic capabilities of our standard two-view chest x-ray. We have robust data that demonstrates the superb diagnostic prowess of bedside ultrasound (US) when compared to the mediocrity of plain films (1, 2,3,4). And yet more information is not always better. Studies examining diagnostic characteristics of a test cannot predict the downstream effects its use will have on patient care. To uncover such consequences, these diagnostic tools have to be tested in the clinical arena. A recent trial did just that.
Published in Chest in 2016, Jones et al examined the effect bedside US had on the diagnosis and management of pneumonia in a pediatric population presenting to the Emergency Department. The authors randomized 191 well appearing children (< 21 years old) in whom the treating physician was concerned for pneumonia, to either a standard work up using a two-view chest x-ray (CXR) or bedside US. These sonographic studies were performed by Pediatric Emergency attendings or fellows, all of whom underwent a 1-hour training course in lung ultrasonography. Patients randomized to the bedside US group were permitted to receive a CXR if the treating or admitting physician felt it was clinically necessary (5).
The authors found a statistically significant reduction (38%) in their primary endpoint, CXR utilization in the patients randomized to the bedside US group. When authors excluded CXRs that were determined to have been performed for non-clinical reasons (requested by admitting physician, parent, guarding or referring physician), bedside US was found to have the potential of reducing CXR utilization by 67%. The authors claim this reduction produced $9,200 in savings. All this with no events of missed pneumonia during the follow-up period (5).
Given US’s superiority to CXR for the diagnosis of pneumonia, these findings are far from surprising (1,2). I imagine similar results would be obtained if the diagnostic capabilities of plain films were compared to CT scan. This trial does provide insight into how the integration of bedside US in general practice may affect clinical management. The authors observed a significant increase in the rate of pneumonia diagnosed in patients randomized to bedside US when compared to the standard treatment arm (28.2% vs 18.1%). This 10% absolute increase consisted completely of diagnoses made by bedside US. In fact, the number of pneumonias diagnosed by CXR in each group was identical (13.6%). Unsurprisingly, this increase in diagnoses coincided directly with a 10% absolute increase in the rate of antibiotic use (37.9% vs 27.3%) in patients randomized to bedside US (5). And yet despite this increase in diagnostic yield, the authors found no difference in clinical outcomes.
This study underscores the subset of sonographically defined pneumonias, that would otherwise go undiagnosed by CXR. In the past these would have been considered bronchitis or URI of viral etiology and treatment with antibiotics would not have been recommended. Given that the clinical outcomes between the two groups were identical, it is reasonable to assume the majority of these would resolve with symptomatic treatment alone. Certainly without bedside US we have not been stricken with a plague of cryptogenic pneumonias undetectable by plain films. US positive, CXR negative pneumonia is a radiographically defined disease that lacks the clinical mass to support its diagnostic reputation. In short, over-diagnosis.
This is not a statistical lark. It is simply the end result of applying a test with more diagnostic accuracy than the one which was previously employed. Furthermore, it is not the first time we have seen the application of bedside US lead to an increase in downstream testing and treatment. In 2014 Laursen et al published an article in Lancet Respiratory Medicine which examined the use of bedside US to evaluate patients presenting to the Emergency Department with shortness of breath. I have discussed this trial in detail in a previous post, but in brief the authors randomized 320 patients presenting to the Emergency Department with respiratory complaints to either a standard work as per the treating physician or the addition of a bedside sonographic assessment of the cardiovascular, pulmonary and deep venous anatomy. Similar to Jones et al, the authors found more pathology in the group randomized to bedside US. These findings led to increased downstream testing and interventions. Despite these changes in management, patients randomized to the bedside US group had a noticeable trend to worse 30-day mortality (12% vs 7% p= 0.13) (6).
I’m sure to some this will appear as an attack against ultrasound, an argument against its use in the Emergency Department. This is of course not the case. Rather this post should be viewed as an examination of the unintended consequences of replacing the old standard with a new more diagnostically robust alternative. Some may argue that the proper response should be to decipher which sonographic findings require antibiotics and which do not. They may very well be right, but I would argue time and time again we have proven ourselves incapable of making such clinical distinctions and will always rule in favor of action.
A test’s true value is not found in its diagnostic accuracy. It cannot be explained simply through its sensitivity or specificity. Rather a test’s worth lies in how it interacts with the surrounding environment, how its is utilized by the clinical operator. Ultrasound is a powerful tool that has already improved many aspects of patient care in the Emergency Department. But its diagnostic prowess comes at the price of information. Information in the form of radiographic disease whose clinical relevance is not always clear. While such findings do not mean we should abandon this valuable bedside tool, it does remind us that it is a test. And like any test we should be mindful in whom it is applied. We owe it to ourselves and our patients not only to hone our skills in the technical aspects of ultrasonography but to understand the downstream consequences of these new found abilities.
- Chavez MA, Shams N, Ellington LE, et al. Lung ultrasound for the diagnosis of pneumonia in adults: a systematic review and meta-analysis. Respir Res. 2014;15:50.
- Pereda MA, Chavez MA, Hooper-miele CC, et al. Lung ultrasound for the diagnosis of pneumonia in children: a meta-analysis. Pediatrics. 2015;135(4):714-22.
- Al Deeb M, Barbic S, Featherstone R, Dankoff J, Barbic D. Point-of-care ultrasonography for the diagnosis of acute cardiogenic pulmonary edema in patients presenting with acute dyspnea: a systematic review and meta-analysis. Acad Emerg Med. 2014;21:(8)843-52.
- Ding W, Shen Y, Yang J, He X, Zhang M. Diagnosis of pneumothorax by radiography and ultrasonography: a meta-analysis. Chest. 2011;140(4):859-66.
- Jones BP, Tay ET, Elikashvili I, et al. Feasibility and Safety of Substituting Lung Ultrasound for Chest X-ray When Diagnosing Pneumonia in Children: A Randomized Controlled Trial. Chest. 2016;
- Laursen et al. Point-of-care ultrasonography in patients admitted with respiratory symptoms: a single-blind, randomised controlled trial The Lancet Respiratory Medicine – 1 August 2014 ( Vol. 2, Issue 8, Pages 638-646)
University of Maryland
Resuscitation Fellowship Graduate