Ultrasound in Austere Environments

From the Prehospital, Austere and Tactical Subcommittee of the Emergency Ultrasound Section

DISCLAIMER: The view(s) expressed herein are those of the author(s) and do not reflect the official policy or position of Brooke Army Medical Center, the U.S. Army Medical Department, the U.S. Army Office of the Surgeon General, the Department of the Army, the Department of the Air Force, or the Department of Defense or the U.S. Government.

Introduction

Whether you are in a pre-hospital setting or working in an austere environment without access to advanced imaging modalities and testing, ultrasound can help you care for your patients. All emergency physicians (EPs) can run a basic workup for shortness of breath, but most of us might have difficulty if a chest x-ray (CXR) or d-dimer was not available. In the same vein, EPs are masters of the crash airway, but most would not be comfortable without end-tidal CO2 to confirm placement or CXR to confirm depth. Ultrasound can help with these workups and guide treatment, as well as influence evacuation decisions from areas with limited medical resources. In this article, we will discuss two cases that took place in austere environments and use these cases to illustrate how ultrasound can be used to improve care for our patients.

Case #1: Shortness of Breath

A patient presented to a small medical treatment facility in Eastern Europe. He reported that he recently flew from the United States and has had several hours of rapidly worsening shortness of breath. The physician on call arrived approximately fifteen minutes after initial presentation. On exam, he was in a tripod position with clear respiratory distress. An initial EKG showed sinus tachycardia without ischemia. A CXR was ordered but there was a significant delay while locating the only local radiology technician. A basic metabolic panel and complete blood count were ordered, but further laboratory testing was not available.

An echocardiogram was performed which showed a significant decrease in ejection fraction. The right ventricle (RV) appeared mildly dilated, but the wall was thick and more consistent with chronic heart failure or pulmonary disease than a pulmonary embolism. An examination of both legs for deep venous thromboembolism (DVT) was negative, further lowering the possibility of a pulmonary embolism (PE). A pulmonary exam was performed which showed diffuse B-lines consistent with pulmonary edema. A diagnosis of acute heart failure exacerbation was made, and the patient was given intravenous furosemide as well as oral nitroglycerin. He was transported to a larger facility and was ultimately repatriated.

Point of Care Echocardiogram

The point of care limited echocardiogram was critical in making the diagnosis of chronic congestive heart failure. Point of care echocardiography is well within the scope of practice of any EP with appropriate training. Previous work has shown good correlation between EPs and Cardiologists when evaluating either normal or significantly decreased ejection fraction using a qualitative evaluation.¹ In this patient, RV dilatation was present and required the physician to differentiate between acute and chronic dilation. Evaluation of the RV is commonly performed as part of an evaluation for PE although it is relatively insensitive for smaller thromboses with a sensitivity of 50% in at least one study.² To further complicate matters, many patients with right heart failure or chronic pulmonary disease have RV dilatation at baseline. Evaluation of the RV free wall thickness in diastole can assist with differentiation between acute and chronic RV dilation. A thickened RV free wall is defined as greater than 5mm as measured in a sub-xiphoid view or the parasternal long-axis view.^3,4 Advanced users may attempt measuring the pulmonary artery systolic pressure, but this may be technically difficult on the small handheld devices available in austere environments. In this patient, the presence of RV dilatation combined with a thick RV wall and a decreased ejection fraction was most consistent with systolic CHF with chronic RV overload.

Pulmonary Ultrasound

The echocardiogram had showed evidence of heart failure, but it was unclear if the current shortness of breath was due to an acute heart failure exacerbation. The presence of diffuse B-lines on pulmonary ultrasound allowed further narrowing of the differential. B-lines are indicative of fluid in the pulmonary tissue.⁵ Greater than three B-lines per lung zone indicate that pathology is present. While B-lines in only one lung zone may indicate pneumonia or infarction, the differential is limited for diffuse B-lines. In the presence of fever and cough, diffuse B-lines may be associated with COVID-19 or a diffuse viral pneumonia.⁶ However, in this setting diffuse B-lines were strongly indicative of pulmonary edema and a CHF exacerbation.⁷

Exam for Deep Venous Thrombosis

Although the case seemed to be a straightforward CHF exacerbation the physician felt that a concomitant PE was possible given the history of recent long-distance travel. Thrombolytics would be an extremely aggressive intervention but were available. Performing a DVT ultrasound contributed more information, allowing the physician in this case to make an informed decision. Quoted sensitivities for point-of-care (POC) DVT exams range widely and may be as low as 70%.^8,9 For this reason most experts recommend combining point-of-care DVT exams with a d-dimer. However, in this setting where a d-dimer is not available, the ultrasound exam alone is of significant utility. In this case, it lowered the physician’s suspicion for PE sufficiently that the risks of thrombolysis were greater than the potential benefits.

The combination of a point of care echocardiogram, pulmonary ultrasound and DVT exam narrowed the differential and the patient received focused appropriate treatment. Without the use of ultrasound, the care of this patient would have been significantly more difficult.

Case 2: Respiratory Failure

A patient presented to a temporary medical facility in a resource-limited location following a hurricane that had caused significant damage to the local infrastructure. The patient was brought by a privately operated vehicle and was unable to give a history. He reportedly told the triage desk that he had difficulty breathing, but shortly after collapsed and was brought to a resuscitation bed. On initial exam, he was in respiratory failure with an oxygen saturation of less than 70% and was in need of emergent intubation. On the first pass the visualized tissue of the posterior oropharynx was noted to be necrotic and the attempt was aborted. The patient proved difficult to ventilate using bag-valve ventilation, and a second attempt was made. On the second attempt, an endotracheal tube (ETT) was placed although it was unclear if the attempt was successful. The patient’s oxygen saturation rose to the low 80s, but he remained difficult to bag. Ultrasound was used to confirm ETT placement and to evaluate for right mainstem intubation. Shortly after, the patient coded with a pulseless electrical rhythm on the monitor. Following three rounds of CPR and epinephrine, cardiac ultrasound was performed which demonstrated cardiac standstill. At that time the code was called. The use of cardiac standstill allowed both for reasonable use of limited resources and to demonstrate to the team evidence for why the resuscitation was not continued.

Ultrasound Confirmation of Endotracheal Tube Placement

If available, quantitative or qualitative end-tidal CO2 is preferred to confirm ETT placement. While waiting for end-tidal CO2 or if end-tidal CO2 is not available, point of care ultrasound can be used. In a 2018 meta-analysis, transtracheal ultrasound was shown to have a positive likelihood ratio of 34.4 for endotracheal intubation.¹⁰ Adding an exam for bilateral lung sliding to rule out right mainstem intubation is an easy addition to the exam and is familiar to any EP as part of the Extended Focused Assessment in Trauma (E-FAST) exam.¹¹ This technique has the potential to improve care in environments without end-tidal CO2, as well as a quick exam during transport if there is concern that the ETT has been advanced or displaced.

Ultrasound for Cardiac Standstill

Deciding to cease resuscitative events is always difficult but may be more so in an area with limited resources or during a mass casualty event as physicians may be unable to continue each resuscitation as long as they normally would. Cardiac standstill has multiple definitions, but one commonly used definition is a lack of movement of the ventricular free wall.¹² Almost any cardiac ultrasound view could be used to evaluate for standstill, but most commonly a subxiphoid or parasternal long axis (PSLA) view is obtained. Cardiac standstill is highly associated with a poor outcome. One study showed a 100% percent positive predictive value for death in the emergency department.¹³ A less discussed reason to perform this exam is to demonstrate to everyone in the room that the heart is not moving. Particularly when working with a young or inexperienced team it can be helpful to demonstrate cardiac standstill prior to stopping CPR.

Conclusions

Ultrasound is very portable and can be of critical importance when other imaging modalities or tests are not available. All physicians involved in mass casualty situations or who find themselves with limited resources can use ultrasound to conserve resources, accurately triage and manage patients appropriately, and ultimately improve the care they deliver to their patients.

References

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Melissa Myers, MD, FACEP±
Associate Professor of the Uniformed Services University; Program Director, Emergency Medicine Ultrasound Fellowship, San Antonio Military Medical Center

Michael Vitto, DO, MS, FACEP
Assistant Director of Clinical Ultrasound; Associate Medical Director of the Center for Human Simulation and Patient Safety; Assistant Professor in the Department of Emergency Medicine, Virginia Commonwealth University School of Medicine