Advanced Hemodynamic and Cardiopulmonary Ultrasound for Critically Ill Patients in the Emergency Department

Interstitial Fluid

Evaluation of the thoracic cavity for interstitial fluid in the setting of acute pulmonary edema, acute respiratory distress syndrome (ARDS), or interstitial pneumonia is best accomplished using either the curvilinear low-frequency probe or the phased array probe. The visualization of vertically oriented B-lines in the upper lung fields is very sensitive for interstitial fluid or edema of the interlobular septa (Figures 2a and 2b).^13,15 In this study, B-lines originate at the pleural line, move with the pleura, and extend off the bottom of the monitor without obliteration (in contrast to A-lines). An isolated B-line may be physiological; however, the presence of several B-lines is consistent with an interstitial pathology. On imaging, the presence of three or more B-lines in a single rib space with a convex probe, or more than six B-lines when utilizing the curvilinear, is considered pathological and referred to as “lung rockets.” B-lines may be focal or diffuse, as seen respectively in cases of pneumonia or acute pulmonary edema.¹⁶ 

Pulmonary Assessment for Fluid Resuscitation

Fluid Resuscitation 

Lung ultrasound studies have been proposed as a means of determining adequate fluid resuscitation and preventing complications associated with excessive fluid. The appearance of diffuse B-lines of acute interstitial syndrome on lung ultrasound can uncover the first signs of extravascular lung water and prevent pulmonary alveolar edema and associated morbidity and mortality.¹⁷ The appearance of an A-line predominance throughout the lung does not predict fluid responsiveness, but rather potential fluid tolerance. 

A benefit of lung ultrasound is that it provides information more rapidly than many of the dynamic measures of fluid responsiveness and cardiac output variability. In addition, lung ultrasound studies are much more easily reproduced than repeating a velocity time integral (VTI) measurements.

Lichtenstein’s FALLS Protocol

Lichtenstein’s FALLS (Fluid Administration Limited by Lung Sonography) protocol provides an approach to performing lung ultrasound on patients presenting in shock.¹² In this approach, lung ultrasound studies are performed after echocardiography to evaluate the patient for causes of obstructive shock. The predominance of B-lines on lung ultrasound suggests cardiogenic shock and, by definition, fluid intolerance. The predominance of A-lines on ultrasound may be present in patients in hypovolemic or septic shock. 

In hypovolemic shock, continued fluid boluses will improve hemodynamics with preserved A-line predominance. In septic shock, B-lines will begin to appear, suggesting that other means of improving forward flow should be initiated.

Consolidation

Chest radiography is known to have variable test characteristics for the detection of pneumonia. Consolidation may not be detected in profoundly immunocompromised or dehydrated patients. Additionally, in critically ill patients, it is often challenging to obtain a posteroanterior and lateral chest X-ray, given the patient’s hemodynamic status and stability for transport, and a single portable anteroposterior film will often miss retrocardiac infiltrates. In both of these clinical settings, POCUS can provide a rapid diagnosis, expediting the care of these septic patients. 

In the presence of a dense consolidation, there may be hepatization of the lung parenchyma (Figure 4b). Additionally, hyperechoic air bronchograms are often visualized. Pneumonia is often associated with pleural effusion and localized B-lines. Using lung ultrasound, rapid bedside detection of these pulmonary findings in clinical presentations suggestive of pneumonia can accelerate appropriate antibiotic and respiratory supportive treatment.  

Left Ventricular Systolic Assessment 

Critically ill patients commonly present with a mixed shock picture, and it is rare for a patient to have solely cardiogenic shock, hemorrhagic shock, etc. Rather, a patient who presents in septic shock may have an underlying cardiomyopathy for which she or he is being treated with a beta-blocker. 

Cardiomyopathy associated with sepsis is common¹⁸ and, at least in the case of diastolic dysfunction, it is underdiagnosed and associated with a higher mortality rate.¹⁹ It is therefore essential that the EP evaluate left ventricular (LV) systolic function rapidly and reliably—particularly in critically ill patients whose disease process may be undifferentiated and whose hemodynamic status is unclear.^20-22 Bedside echocardiography by the EP is invaluable in identifying the LV contribution to the hemodynamic profile and tailoring resuscitation to optimize patient outcomes. 

Although gross visual assessment is the most widely used method by which EPs estimate LV systolic function, this strategy is subjective, operator-dependent, and requires at least two quality views to understand the heart’s three-dimensional movement. However, when faced with a rapid diagnostic dilemma, a global visual estimate of the overall contractility (hyperdynamic, normal, depressed, severely depressed) may be more useful than estimating the ejection fraction (EF), especially when the patient’s baseline EF is unknown.