Thoracic ultrasound in respiratory distress
Another tool in the diagnostician’s briefcase
This article originally appeared in the National Association of EMS Physicians blog and is reprinted here with permission.
By Emily Fitzgerald, MD
Your ALS crew is dispatched to a local nursing home for the 74-year-old female with shortness of breath, priority 2. You arrive on scene to find an elderly woman in respiratory distress. She is tripoding in bed, has marked accessory muscle usage and can only nod yes/no to questions due to her severe tachypnea.
You perform a rapid physical exam. On auscultation, you find she is tachycardic with an irregular rhythm and has no murmurs/rubs/gallops. She has poor air movement with diminished breath sounds bilaterally but you appreciate a faint expiratory wheeze. You note 2+ pitting edema in her bilateral lower extremities.
Facility staff tells you that she has a history of chronic obstructive pulmonary disease (COPD) on 3L of oxygen at baseline, congestive heart failure (CHF), and hypertension. For the past 4 days, she has had increased dyspnea on exertion, developed a new productive cough, and has been using her albuterol inhaler every 2 hours. They checked on her this morning, found her as described, and called 911.
Her initial vitals are BP 196/107, HR 126, RR 33, SpO2 84% on 3L, EtCO2 60. Based on this history and physical exam, can you confidently determine whether this patient’s respiratory distress is primarily due to a CHF versus a COPD exacerbation to implement a targeted treatment plan?
Dyspnea is one of the most common presentations to the emergency department. The two most common discharge diagnoses after initial presentation with shortness of breath are COPD exacerbation and CHF exacerbation . COPD and CHF affect 15.9 and 6.5 million United States adults respectively and, when combined, account for 1.5 million ED visits annually .
Approximately 21% of U.S. adults have co-morbid COPD and CHF . These patients present with similar signs and symptoms that result in great difficulty differentiating between these etiologies solely based on history and physical exam data. Previous research has shown that emergency medicine physicians misdiagnose and mistreat 31-32% of these patients which results in increased morbidity and mortality .
The treatment pathways for these two conditions diverge early in the management course. Although both conditions improve with non-invasive positive pressure ventilation (CPAP or BiPAP), COPD is better controlled with bronchodilators and steroids while CHF exacerbations typically improve with preload and afterload reduction through administration of Nitroglycerin. The diversity of the disease pathophysiology and subsequent treatment mechanisms requires that a clinical choice be made early in the patient assessment. If there is a lack of clarity, the patient may receive all available treatments, further obscuring the clinical picture and resulting in potential harm.
Thoracic point-of-care ultrasound (POCUS)
Thoracic POCUS has been identified in many previous studies as being able to differentiate between CHF and COPD exacerbation . When evaluating for pulmonary edema, lung ultrasound is predominantly performed using the curvilinear or phased array probe which are lower frequency probes that penetrate deeper into tissue. Ultrasound does not scan well through gas; it reflects off of the air in the lungs, creating artifact.
The two important artifacts to assess for are A-lines and B-lines. A-lines are normal findings in healthy lungs. Finding ≥ 3 B-lines within one zone of the lung signifies that there is increased tissue density, also known as lung consolidation. The most common cause of this consolidation is pulmonary edema from CHF. Other potential causes include pneumonia, interstitial lung disease, pulmonary contusion, and atelectasis. In the correct clinical setting, the absence of B-lines suggests the patient’s symptoms are more likely caused by a COPD exacerbation.
For an excellent Thoracic POCUS training resource, follow this link to EMRAP’s video entitled Ultrasound of Pulmonary Edema .
Implementation of thoracic POCUS in the field
Prehospital-focused researchers across the country are studying how to best adapt this technology for use in EMS. A prospective observational pilot study published in 2021 enrolled 63 paramedics into a thoracic POCUS training program which involved a 90 minute didactic session and a 2-3 hour session scanning ED patients . These paramedics then obtained and interpreted images from 65 patients with chief complaint of shortness of breath during their transportation to a hospital via ambulance. The paramedic’s field diagnosis was compared to the patient’s hospital diagnosis.
The presence of bilateral B-lines for diagnosis of CHF yielded a sensitivity of 80% and specificity of 72% while the presence of any B-lines was 93% sensitive and 50% specific for CHF. Comparison of paramedic and ultrasound-trained faculty image interpretations showed good inter-rater reliability for the detection of B-lines with a k=0.60. This study demonstrated that thoracic POCUS performed by paramedics in the field is likely feasible and the detection of B-lines has acceptable sensitivity and specificity in diagnosing CHF/pulmonary edema while the absence of B-lines is likely to exclude significant decompensated heart failure. Unfortunately, this study could not comment on whether thoracic POCUS effectively altered the paramedics’ treatment plans.
Another prehospital research team evaluated the use of thoracic POCUS in differing driving conditions. In this prospective educational intervention study, 17 paramedics underwent a thoracic POCUS training program during which they attended a 45-minute lecture and completed 25 supervised scans . The paramedics then performed scans (both simulated and on standardized patients) while they were in the back of an ambulance as it progressed through multiple driving patterns (parked, constant acceleration, start-stop, serpentine).
The investigators found there was no statistically significant difference in the time needed to obtain a simulated image, in the correct clinical interpretation of the simulation images, or in the image quality scores across all driving conditions. This study suggests that thoracic POCUS implementation is feasible as paramedics obtained acceptable images and accurately interpreted them in a realistic simulation environment.
Implementing thoracic POCUS in any system will involve considerable start-up costs and time investment on the part of providers and training faculty. It is important to acknowledge that acquiring these images may take compete with other patient care tasks. Therefore, prior to wide-spread employment of this technology, we need to ensure this procedure reliably and positively impacts patient management. As data on this topic is becoming increasingly robust, EMS leadership throughout the country must consider how they might adopt, implement, and monitor this technology within their unique systems.
You immediately recognize this patient is in respiratory distress and initiate CPAP. She tolerates CPAP well; her work of breathing and tachypnea improve. While your partner notifies the hospital of your impending arrival, you perform a thoracic POCUS. With your curvilinear probe, you scan lung zones 4 and 6 bilaterally and see > 3 B-lines in each of these zones. CHF exacerbation becomes your leading diagnosis, and you administer Nitroglycerin per regional protocol. Her BP decreases to 162/94. On repeat lung exam, you appreciate increased air movement with coarse rhonchi at the bilateral bases. You decide not to administer DuoNebs or Decadron at this time.
Upon arrival to the ED, your patient is triaged to their critical care section. She is transitioned to a BiPAP mask, placed on a Nitroglycerin drip, and diuresed with Furosemide. They are able to transition her off the BiPAP and she is admitted to the cardiology floor in stable condition. Hospital physicians diagnose this patient with flash pulmonary edema that was triggered by severe hypertension in the setting of decompensated CHF. Her medication regimen is optimized, and she is discharged 5 days later.
Assessing shortness of breath
Acute dyspnea has a differential diagnosis; providers must utilize targeted patient assessment and objective data to generate a clinical impression and decide on a treatment plan. Thoracic POCUS is routinely used by emergency medicine clinicians to gather additional data to aid in the assessment of undifferentiated shortness of breath. There is currently national traction to adapt this technology for use in EMS and some EMS systems have already implemented the technology.
Although preliminary data is promising, the EMS community must continue to research and monitor the utility of this technology in the prehospital setting to transform patient management and outcomes, as well as what the magnitude of that impact might be given the cost of training, implementation and the necessary quality improvement work that must accompany the introduction of novel technologies (see NAEMSP’s position statement on introduction of novel technologies here) . We anticipate this will be an advantageous tool in the paramedic’s diagnostic arsenal.
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- Avila, J. (2016, October 3). Ultrasound of Pulmonary Edema. EMRAP Medical. Retrieved January 18, 2022, from https://www.youtube.com/watch?v=VzgX9ihnmec
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- Maloney, L. M., Williams, D. W., Reardon, L., Marshall, R. T., Alian, A., Boyle, J., & Secko, M. (2020). Utility of different lung ultrasound simulation modalities used by paramedics during varied ambulance driving conditions. Prehospital and Disaster Medicine, 36(1), 42–46. https://doi.org/10.1017/s1049023x20001247
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About the author
Emily Fitzgerald, MD, is currently a second-year resident in Emergency Medicine at the University of Rochester in Rochester, NY. Her professional interests include prehospital medicine with a focus on prehospital education and critical care transportation.
Edited by EMS MEd Editor, Maia Dorsett @maiadorsett
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