Ultrasound management in the emergency department: a narrative review

Introduction

Point-of-care ultrasound (POCUS) represents a goal-directed ultrasound (US) examination used in emergency departments, where US allows physicians to make quick diagnoses. This tool is able to increase diagnostic accuracy and significantly reduce the time between patient arrival and the diagnosis (and so, the beginning of an appropriate treatment), when applied in the clinical context.

POCUS is also used by emergency medicine (EM) physicians for real-time invasive procedures to improve patient safety, such as during chest drainage position, pericardiocentesis and central line insertion.

Bedside US have been used to shed light on patient’s fluid management by observing elevated left ventricular end diastolic pressure (LVEDP) and fluid intolerance by checking the presence of B-lines as an early sign of extra vascular lung water (EVLW) in acute decompensated heart failure (ADHF) or in acute respiratory distress syndrome (ARDS).

The American College of Emergency Physicians (ACEP) published the first Emergency Ultrasound Guidelines to describe the principal POCUS applications and underline the importance of continuing education and training in emergency US (1,2).

Today, POCUS refers to a bedside examination using US probes, through which, integrated with clinical information, physicians can make decisions on the patient’s management and therapy, but it requires experience and expertise in the acquisition and interpretation of images (3).

The use of POCUS in emergency department at the patient’s bedside during last 20 years has increased as well as the skills of the emergency physician due to the increased opportunity for training. The heart and vessel district, the lung, and the trans-cranial Doppler in compliance with consensus and expert recommendations of the European Society of Intensive Care Medicine (ESICM) 2021 have also contributed to the diffusion in its use in critical ill patients.

The principal role of POCUS in the emergency department is also to identify an immediate life-threatening condition leading to hemodynamic instability through implementation of standardized protocols such as the rapid ultrasound for shock and hypotension (RUSH) and the extended-focused assessment with sonography in trauma (E-FAST) protocols (1-4). We present this article in accordance with the Narrative Review reporting checklist (available at https://jphe.amegroups.com/article/view/10.21037/jphe-24-5/rc).

Methods

A systematic literature search was conducted on PubMed/Medline databases, choosing the related MeSH terms: ultrasound, emergency department, shock, dyspnea. We included English-language publications, reviews, and meta-analysis from January 1995 to December 2023 on clinical use of ultrasonography in critical patients (Table 1).

This narrative review discusses the most common applications of POCUS in the emergency setting. It emphasizes the use of immediate and fast-focused US at the patient’s bedside for diagnostic or therapeutic purposes and its applications in daily clinical practice, for example goal-directed echocardiography (GDE) during cardiac arrest, thoracic ultrasonography, deep vein thrombosis (DVT) and pulmonary embolism evaluation. At the same time, the US is able to screen abdominal, ocular and neck regions, obstetric problems, musculoskeletal system and fluid needs. We aim to improve the diagnostic flow process on critical pathologies in emergency room (ER).

POCUS in the head and neck region in the ER

POCUS in the head and neck region plays a significant role in the diagnosis and treatment of several conditions—listed below—in the ER because it allows a quick and repeatable overview even in peripheral hospital structures (remote areas, low-income countries, combat fields, sports areas etc.) (4,5).

Ocular ultrasonography

Ocular ultrasonography can be a potentially helpful approach to evaluate intracranial pressure (ICP) by measuring the optic nerve sheath (ONS) (6). The ONS is an extension of the dura mater and the subarachnoid space; therefore, an increase in the ICP is reflected in its diameter. The study requires a high-frequency linear probe and the optic nerve sheath diameter (ONSD) is evaluated through the transorbital window. It appears as a hypodense, linear structure, approximately 3 mm posterior to the globe. The cut-off value of this diameter is 5 mm. Most studies agree with the statement that a higher value may correlate with an ICP greater than 20 mmHg (7).

However, a recent expert consensus established that, despite ONSD measured by ocular ultrasonography is undoubtedly a promising technique, there are no recommendations for its routine use as it is considered a too advanced skill, thus reserved for a few experts (8). Ocular ultrasonography has 84% sensitivity for any intracranial injury in head trauma, when compared with computed tomography (CT) scan (4).

Transcranial Doppler (TCD) and B-mode transcranial color-coded duplex (TCCD)

TCD and TCCD cannot be considered as a substitute for invasive measurement, although in recent decades, these techniques have acquired an increasing role in the diagnosis of intracranial space-occupying lesions, in the assessment of ICP and central perfusion pressure, especially when indications are unclear or invasive methods are not available (9). TCD and TCCD can be used to evaluate midline shift, vasospasm, raised intracranial hypertension and cerebral circulatory arrest (8). A TCD examination may be performed positioning the patient supine and maintaining head-of-bed elevation >30 degrees; then, a 1–5 MHz US phased array transducer is chosen, if available; otherwise, a cardiac probe can be used. Most information can be obtained by interrogating the middle cerebral artery through the temporal approach. Other commonly employed acoustic windows are the transorbital, occipital and submandibular windows (10). B-mode TCCD insonation of the middle cerebral artery might be recommended as a basic skill for intensivists to rule out intracranial hypertension, as suggested by ESICM for the Intensivists (8).

Neck US

The study of the neck and its structures can be part of the general POCUS in the ER (11); in particular, it is helpful in case of dyspnea that occurs in the upper airways (stenosis, swelling, inflammatory disease of the upper airways, bilateral vocal cord paralysis and foreign bodies). A high-frequency (10 MHz) US linear probe can be used. Even if severe airway obstruction is an emergency, some authors recommend the entire neck fast scan.

Many recent studies focused on evaluating the utility of ultrasonography to identify the endotracheal tube (ETT) position during intubation. However, further studies are needed to validate the clinical utility of applying bedside real-time tracheal ultrasonography (12-15).

Emergency US

US can be used to quickly evaluate patients with respiratory insufficiency from different aetiology, such as interstitial syndrome, pleural effusion (PE), pneumothorax (PNX), loss of pulmonary aeration, consolidation, and pneumonia (3,16-18). Compared to chest radiography, US is superior in evaluating PE, PNX, alveolus-interstitial syndromes, and pneumonia. The text below provides a summary of the most common pleuro-pulmonary diseases associated with acute respiratory failure in patients presenting to the emergency area.

PNX

US allows you to make a diagnosis through three signs (3):

• The absence of pleural sliding is detectable in M-mode with the disappearance of the seashore phenomenon (Figure 1). This sign can also be evident in other conditions, such as lung atelectasis, pleural adhesions, apnea and cardiorespiratory arrest. The presence of sliding has a low specificity (60–90%).
• Absence of B lines artifacts and lung pulse.
• The presence of the lung point is a specific sign that indicates the interface where the lung resumes contact with the two pleural layers, the specificity of which is 100%.

Figure 1 The distinctive “barcode sign” and “sea shore” visualized in pulmonary ultrasound.

Ultrasonography would be good to use to exclude PNX by looking for lung sliding lung pulse and/or B lines and identifying the lung point, as well as chest drain insertion as suggested by ESICM for the intensivists.

PE

PE is certainly the pathology that best lends itself to US study (19); in the literature, it is amply demonstrated that lung US represents the gold standard in diagnosing PE (20). In this condition, the US study has very high sensitivity and specificity; it allows you to “correctly” evaluate the volume of the effusion [formula of Balik et al. (21)] and its characteristics: transudative effusions are usually bilateral with normal pleural thickness, exudative effusions (presence of fibrin, cells, debris in suspension produces echoes or sediments that are moving in the fluid. It is called the “plankton sign” or the “hematocrit sign”) (21-24). The convex probe is the preferred choice, because it gives a better overview; the fluid appears as hypo/anechoic (Figure 2). The optimal site to detect a non-localized PE is located on the posterior axillary line above the diaphragm. It is essential to identify the diaphragm to avoid diagnostic mistakes with abdominal effusions.

Figure 2 Ultrasound image revealing a pleural effusion.

Ultrasonography would be useful to: (I) highlight the presence of anechoic regions above the diaphragm; (II) estimate the volume of PEs and (III) find the best position for PE drainage as suggested by ESICM for the intensivists.

Interstitial syndrome/pulmonary consolidation

The presence of pulmonary aeration loss can have different US aspects (25-30), such as:

• Interstitial syndrome (Figure 3), where there is the presence of US artifacts named B-lines, defined as “laser, vertical, hyperechoic artifacts arising from the pleural line that extends to the lower part screen and move in synchrony with lung sliding; they are considered as pathological findings when they are present in great number (three or more) in the space between two ribs”. The absolute number of B-lines correlates with disease severity and pulmonary aeration loss. Evaluation of B-lines is performed by using convex probe.
• Lung consolidation appears as a subpleural region with irregular margins, poor in echoes or with a liver-like aspect (“hepatization” of the lung) depending on the air leak and the predominance of fluid. We can find dynamic and static air bronchograms within the consolidation. If the consolidation does not reach the pleural line and is located deep in the lung parenchyma, ultrasonography fails to find it. Another possible form of lung consolidation is the “nontranslobar consolidation”, in which hypoechogenic subpleural areas with irregular margins can be observed (recognizable in the form of what is called a “shred sign”) (Figure 4). Dynamic air bronchograms from the US point of view are a sign of pneumonia with high specificity (Figure 5) (along with typical clinical signs such as dyspnea and chest pain), making possible a differential diagnosis with other types of consolidation such as atelectasis, pulmonary infarction, and cancer.

Figure 3 Ultrasound image capturing intricate B-lines (*) in the lung.

Figure 4 Ultrasound image depicting a notable shred sign and subpleural consolidation, highlighted by arrows.

Figure 5 Ultrasound image of the lung with consolidation and air bronchograms.

Ultrasonography would be helpful for the evaluation of respiratory failure/reduction of lung aeration, by looking for signs of interstitial syndrome (B-pattern) or lung consolidation (tissue like pattern, subpleural pattern).

In the acute clinical condition, we can make the differential diagnosis between acute cardiogenic pulmonary edema (ACPE) and acute lung injury (ALI) or ARDS. In the first case, there is a thickness pleural line with sliding and a homogeneous distribution involving both anterior and posterior lung fields; the other conditions are characterized by an irregular pleural line thickened in some zones in a heterogeneous echotexture like B-lines (31).

Diaphragmatic dysfunction (DD)

DD is defined as a loss of muscle strength that can be partial (weakness) or complete (paralysis), resulting in reduced inspiratory capacity and decreased resistance of the respiratory muscles. Diaphragmatic US is a valuable technique for evaluating the anatomy and function of the diaphragm, primarily diaphragm excursion and thickening (31).

It measures right hemidiaphragm excursion using the anterior subcostal view with the convex probe positioned under the costal margin between the midclavicular line (MCL) and the anterior axillary line at the 9th intercostal space. Paralysis can be diagnosed by identifying the absence of diaphragmatic motion during quiet and deep breathing and paradoxical motion during deep breathing or voluntary sniffing (32,33). Diaphragmatic weakness (diaphragmatic excursion <10 mm, or thickening <10%) can be diagnosed by identifying impaired mobility during deep breathing, with or without paradoxical movement during voluntary sniffing (34,35). Ultrasonography would be advantageous to study the excursion of the diaphragm as an index of its functionality, particularly in the attempt of weaning patients from mechanical ventilation.

POCUS as a guide to invasive procedures in critically ill patients

In the emergency area, the use of the US can help the intensivist doctor or emergency doctor in cannulating a central vein as an internal jugular vein (36), positioning a pleural drainage, the ETT (37,38), or carrying out a percutaneous tracheostomy (39).

Ultrasonography can help us during cannulation of arterial and venous vessels after various failed blind attempts, as well as to exclude DVT in patients with risk factors when compression is applied on the femoral and popliteal vein.

Bedside lung ultrasound in emergency (BLUE) protocol

Lung ultrasonography is quickly available at the bedside, allows for real-time evaluation, and has radiation-free hazards compared to conventional lung imaging modalities in critically ill patients (40). The BLUE protocol (Figure 6) is based exclusively on lung and venous US scans (41). It is a protocol adopted in acutely dyspneic or hypoxemic patients because it gives an instant view about the state of the lungs, thus conditioning diagnostic and therapeutic decisions, with a documented accuracy of 90.5%. It can be performed with both linear and curvilinear probes; each hemithorax is divided into anterior (from sternum to anterior axillary line), lateral (between anterior and posterior axillary line), and posterolateral alveolar pleural syndrome (PLAPS) point; so, each lung is divided into six zones. The BLUE-protocol provides an excellent step-by-step approach to diagnose acute dyspnea (42). It starts with checking for anterior lung sliding because its presence leads to exclude PNX and confirms the “normal lung”, defined by the presence of A-lines and lung sliding. The venous scan facilitates the diagnosis of pulmonary embolism with 81% sensitivity and 99% specificity. The B-profile suggests pulmonary edema. The C-profile indicates anterior lung consolidation, regardless of size and number. The PLAPS profile designates posterolateral alveolar and pleural syndrome. Finally, we can have combined profiles, like the A/B profile or A-V-PLAPS profile (43).

Figure 6 BLUE protocol flowchart. PLAPS, posterolateral alveolar pleural syndrome; COPD, chronic obstructive pulmonary disease; BLUE, bedside lung ultrasound in emergency.

Goal-directed echocardiography (GDE)

GDE is performed by using a low-frequency phased array probe (3–5 MHz) (44). The emergency physician evaluates heart anatomy and function during hemodynamic derangement. The GDE competence statement consists of five standard views: parasternal long-axis (PLAX), parasternal short-axis (PSAX), apical four-chamber (A4C), apical two-chamber (A2C), substernal or subxiphoid view and inferior vena cava (IVC) views. In addition, a color Doppler of aortic and mitral valves can be performed. The goals of GDE are:

• Identification of life-threatening causes of hemodynamic failure, such as major valve failure, pericardial tamponade, severe reduction in left ventricular function, or massive pulmonary embolism.
• Categorization of shock state and initial management strategy. The five views of GDE permit the intensivist to categorize shock as hypovolemic, distributive, cardiogenic, or obstructive. That leads to rational management strategies and identification of the cause of the hemodynamic failure.
• Identification of coexisting diagnoses.

The diagnostic utility of GDE has also been validated for evaluating undifferentiated shock (45,46). GDE is usually combined with thoracic ultrasonography for the evaluation of respiratory failure (47); nevertheless, POCUS can be helpful as a monitoring tool during cardiopulmonary resuscitation (CPR).

Sonography assessment should not delay or interrupt the delivery of high-quality CPR. Thus, it requires the operator to be skilled in rapid image acquisition within the 10-second pulse check pause (i.e., seek a palpable pulse) during CPR (48,49). The main recommendations of the ESICM for cardiac evaluation are listed below (8).

Quantify cardiac size and systolic function deficit

The systolic function of the left ventricle can be increased, decreased or normal; it can be evaluated by calculating the ejection fraction that reflects the volume of blood expelled from the ventricle at each beat. The ejection fraction is calculated with the modified Simpson method or by visual inspection only (“eyeballing”); it is a very reliable method when used by expert doctors. We can also estimate the cardiac output as the product of heart rate and stroke volume (SV) [velocity time integral (VTI) of the transvalvular aortic systolic flow velocity curve obtained from an apical projection with pulsed hemodynamic Doppler, multiplied by the diameter of the outflow tract of the left ventricle, brought in a left parasternal projection in long axis]. We must also evaluate an abnormality in the regional wall movement that may suggest coronary syndrome (8).

Acute alterations of left ventricular valvulopathies

Evaluation of the cardiac valves of the left ventricle, vegetations, prostheses, perforations, stenotic or insufficiency-type pathologies of the aortic and mitral valves and color Doppler are not considered priority skills and should be discuss with the cardiologist (8) (Figures 7,8).

Figure 7 Cardiac ultrasound depicting mitral valve insufficiency. MR, mitral regurgitation; VTI, velocity time integral; PG, pressure gradient.

Figure 8 Cardiac ultrasound image revealing mitral valve insufficiency with Doppler-highlighted regurgitation. This diagnostic visualization provides a detailed insight into the presence and severity of mitral valve regurgitation. MR, mitral regurgitation; ERO, effective regurgitant orifice.

Diastolic function of the left ventricle

The transmitral pulsed wave Doppler calculates the blood flow velocity from the atrium to the left ventricle during the diastolic filling period by placing the sample volume on the tip of the mitral leaflet. The normal profile is characterized by two peaks, E and A (50). The E-wave (early) represents the maximum flow velocity during the left ventricle’s rapid or passive filling phase, and the A-wave (atrial) is the maximum velocity of transmitral flow during the end-diastolic phase due to atrial contraction (Figure 9). There are 4 diastolic function profiles.

• Normal diastolic pattern: E/A ratio higher than 1.
• Mild diastolic pattern: E/A ratio <1 and deceleration time E wave (DTE) >240 msec.
• Pseudo-normal diastolic pattern: E/A ratio >1 and DTE <150 msec.
• Restrictive diastolic pattern: E/A ratio >2 and DTE <160 msec.

Figure 9 Echocardiography with E/A ratio curves. This depiction illustrates the ratio of early to late ventricular filling velocities, providing valuable insights into diastolic function. E, early; A, atrial.

Evaluation of right ventricular function deficit

The systolic function of the right ventricle can be estimated by evaluating the reduction in the cavity area (normal >1/3) and the tricuspid annular plane systolic excursion in M-mode [tricuspidal annular plane systolic excursion (TAPSE) >15 mm]. In case of suspected pulmonary embolism, it is possible to calculate the ratio between the right and left ventricle in size, the area at the end of diastole in four-chamber and parasternal longitudinal projection; it can also be displayed paradoxical movement and flattening of the interventricular septum and dilatation and hypo-collapsibility or non-collapsibility of the IVC. McConnell’s sign, described as right ventricular free wall hypokinesia and normal apical contractility, is a specific sign of pulmonary embolism when associated with right ventricular enlargement and a consistent clinical picture of dyspnea and DVT (50).

Evaluation of the hemodynamic impact of the pericardial effusion

To evaluate the hemodynamic impact of the pericardial effusion, it is possible to analyze the systolic collapse of the right atrium or the diastolic collapse of right ventricle (RV) on an A4C or subcostal view and the size and dilatation of the IVC (50) (Figures 10,11).

Figure 10 Human heart in diastole captured through ultrasound imaging pericardial effusion.

Figure 11 Human heart in systole captured through ultrasound imaging pericardial effusion.

Ultrasonography can help to evaluate the severity of systolic and diastolic dysfunction, the volume of pericardial effusion associated with important hemodynamic changes as well as the presence of left valvular heart diseases. An US scan can determine: (I) the degree of systolic dysfunction as normal or decreased contractility of the left ventricle using PLAX, PSAX, A4C and A2C views; (II) regional wall motion abnormalities such as in acute coronary syndromes; (III) SV with the evaluation of the left ventricular outflow tract (LVOT); (IV) massive pulmonary embolism by right ventricular abnormal size assessment; (V) paradoxical septal motion, RV and IVC dilatation as parameters of right ventricular systolic dysfunction.

Assessment of severe hypovolemia

In case of hypovolemia, we can use ultrasonography to observe the small diameter and the collapse of the IVC, with small dimensions of the ventricular chambers and their obliteration during systole. In hypovolemic shock, US shows a typical triad: small and hyperkinetic cardiac chambers, mild IVC and “dry” lungs with A-lines. Some causes of hemorrhagic shock such as hemothorax, hemoperitoneum, abdominal aortic aneurism can be diagnosed with US as well as fluid management by monitoring the heart, the IVC and lung patterns (51).

POCUS in the abdominal region in the ER

Many patients have a non-pathologic physical examination or are unconscious at their admission to the ER. Despite that, they can hide many life-threatening conditions that must be detected and treated immediately. Focused assessment with sonography in trauma (FAST) US was introduced in 1996 as an alternative to peritoneal lavage (52). In 2006, the American College of Surgeons Committee on Trauma introduced the FAST exam in advanced trauma life support (ATLS) guidelines (53). The FAST scan is used to properly triage patients for surgical or medical management in the ER: it focuses on detecting any sign of severe life-threatening conditions underlying acute abdomen such as aneurysm rupture, abdominal injury after blunt trauma, hollow viscus perforation and bleeding from ectopic pregnancy.

The FAST scan consists of four abdominal views (54): right upper quadrant, left upper quadrant, suprapubic region and subxiphoid approach to the pericardium. A 3–6 MHz convex probe is usually chosen and placed with the index mark oriented to the patient’s head, from the subxiphoid line to the medium axillary line on the right and the posterior axillary line on the left. This position provides a coronal view of the Morison’s pouch, the liver with the gallbladder and the right kidney, while it provides a coronal view of the Koller’s pouch, the spleen and the kidney, to the left. The exam should also include a view of the diaphragm. The pubic symphysis is the external landmark for the probe to obtain the pelvic view: it is placed in the midline in the long and short axis to evaluate the pouch of Douglas and the bladder.

Acute abdomen

Suspected acute abdomen is one of the most common reasons for ER admission. US examination is used to triage patients: the most common causes are acute cholecystitis, hepatitis, pancreatitis, appendicitis, diverticulitis or other inflammatory bowel diseases, urolithiasis and hydronephrosis and life-treating conditions such as ruptured aortic aneurism, intestinal obstruction or perforation, and ectopic pregnancy. US-based algorithms reduced ordering of CT scans by 50%: random-effects right dimension (RD) −0.52 [95% confidence interval (CI): −0.83 to 0.21], but the significance of this finding is unclear (55). Abdominal US, but not used alone, is recommended to find the cause underlying a surgical abdomen because it is not able of distinguish among different etiologies (perforation, bowel obstruction), as suggested by ESICM.

Intraperitoneal free fluid (IPF)

The presence of IPF is not an uncommon finding in ER patients as it occurs in various diseases such as blunt trauma, ruptured abdominal aortic aneurysm, ascites, urine leak or ectopic pregnancy. The FAST examination should be considered an essential skill for intensivists. It is strongly recommended (8) to identify the pathological presence of free fluid or blood in traumatic acute abdomen: in experienced hands, the US has over 90% specificity (56) in detecting free intraperitoneal fluid but a poor sensitivity (60–80%) (57). The fluid appears anechoic and often localized in Morison’s pouch, between the kidney and the liver, in the peri-splenic space, in the subphrenic region or in Douglas’s pouch. Although IPF is simple to detect, it is often difficult to determine its nature: blood, ascites, bile, or urine. Abdominal US should always be integrated with a clinical assessment: in trauma patients, it can be easily performed at admission and repeated according to the evolution of the patient clinical status, but it must not delay CT scan, which remains the gold standard for trauma patients. CT scan is mandatory in suspected multiple traumas and, apart from a significant reduction in the frequency of ordering CT scans, no beneficial effect of US has been found on patient-centred endpoints (55). Abdominal US can be used as a guide to paracentesis: it confirms the clinical suspicion and facilitates the aspiration of fluids, reducing procedure-related complications. In a randomized trial, paracentesis through US guidance has been found to have a 95% success rate, compared with 61% using the landmark method (58).

Cholecystitis

Cholelithiasis is the first cause of cholecystitis (among 95% of all causes) (59). The US is the gold standard for its diagnosis: POCUS has 89.8% sensitivity and 88% specificity for the diagnosis of cholelithiasis (60), and enlarged gallbladder with thick and stratified walls, or presence of gallstones or sludge, pericholecystic fluid or dilatation of the common bile duct, in a patient with positive Murphy’s sign, are highly suspected for cholecystitis (56).

Bowel

Bowel obstruction and perforation represent severe surgical emergencies: in case of high suspicion, patients with acute abdominal pain can undergo POCUS as a supplement to the physical examination to triage them appropriately and not delay an urgent CT scan, that remains the gold standard exam. Sonography, provided by experienced clinicians, has a high sensitivity (90% for bowel obstruction and 93% for pneumoperitoneum) and specificity (96% for bowel obstruction and 64% for pneumoperitoneum) (61,62). However, there are no recommendations on its routinary use due to the extensive experience needed to achieve a good technique.

Appendicitis

Appendicitis is the most common surgical emergency and the first cause of acute abdomen in younger patients. The diagnosis of appendicitis requires clinical, laboratory and radiological findings. CT scan is still the most common method used to diagnose it (sensitivity 91–98.5%, specificity 90–98%) (63), but unfortunately, in crowded ERs, its execution may be delayed. Then, the use of POCUS can save time, which is crucial for complications such as perforation or septic shock. The POCUS, performed by skilled emergency clinicians, has shown similar accuracy to radiologist-conducted exams (sensitivity 95%, specificity 95%) (64).

Kidney

The renal system is well visualized with US and its use has been strongly recommended by the American Institute of Ultrasound in Medicine (65) for the evaluation of suspected acute renal colic. When a patient complains about cramping, severe unilateral pain, nausea, and fever at the admission to emergency department, US can be used to confirm or exclude the presence of urinary tract obstruction and hydronephrosis. Both the kidneys must be assessed with the bladder with B-mode in the short and long axis (8), and the ureters must be evaluated, searching for internal obstruction or external compression. Literature shows that POCUS examination has a high sensitivity (>95%) (66) and specificity (73% to 98%) in detecting hydronephrosis (56). POCUS is also recommended for the qualitative assessment of the bladder’s urine volume and the Foley catheter’s correct positioning.

Aortic abdominal aneurysm (AAA)

US screening for abdominal aortic aneurysms is comparable to CT scan and magnetic resonance imaging (MRI), is cost-effective, non-ionizing and with no adverse reactions. AAA can mimic many other causes of acute abdomen, such as acute renal colic or acute bowel disease. The medical triad of acute pain, shock and a tender pulsatile epigastric mass is highly suspected for a ruptured aortic aneurysm. POCUS has shown 94% to 99% sensibility and 98% to 100% specificity in detecting AAA (56): the scan should begin from the epigastrium to the aortic bifurcation and should include a color-Doppler study.

Ultrasonography would be useful at the mesogastrium and epigastrium level to highlight abdominal aortic aneurysm in case of undiagnosed shock as suggested by ESICM for intensivists.

Ultrasonography in obstetrics

POCUS can be used to assess pregnancy status and rule out red flags such as ectopic pregnancy, fetal complications, or stillbirth. It can also help with the identification of the etiology of abnormal vaginal bleeding, complete and incomplete abortion, blighted, ovum, and ectopic pregnancy (4).

Thus, it is an ideal clinical tool for rural and remote communities. POCUS can decrease some of the healthcare burdens in these communities and improve maternal and fetal patient-care outcomes (67). Furthermore, timely US screening and point-of-care bedside assessment can significantly reduce maternal and fetal risk factors, thus enhancing morbidity and mortality (68). One meta-analysis found that the US has a sensitivity of 99.3% in detecting an ectopic pregnancy with a negative predictive value of 99.96% (69).

Shock US protocol

Shock is a state of organ hypoperfusion resulting in cell dysfunction, multiorgan failure (MOF) and death. Mechanisms underlying the development of this condition may involve the reduction of circulating volume, cardiac output, and vasodilatation, sometimes excluding the capillary bed from blood perfusion. Symptoms include altered mental status, tachycardia, hypotension, and oliguria. Diagnosis is clinical, including measurement of blood pressure and sometimes measurement of markers of tissue hypoperfusion (e.g., blood lactate, base deficiency). There are mainly four broad categories of shock (51,70). The principal role of POCUS in this emergency setting is the rapid assessment of patients with hemodynamic instability through standardized protocols such as the RUSH, the fluid administration limited by lung sonography (FALLS), and the E-FAST protocols (71).

E-FAST

E-FAST is a bedside US protocol designed to detect peritoneal fluid, pericardial fluid, PNX, and hemothorax in a trauma patient. Sonography for trauma would be useful to assess the presence of free peritoneal fluid or blood in traumatic abdomen.

There are three indications:

• Blunt abdominal trauma, hemodynamically unstable.
• Penetrating trauma of the thoraco-abdominal district, where it is unclear whether there has been penetration into the abdomen cavity.
• Hemodynamically unstable patients with unknown causes.

For the abdominal scan, we may use the FAST approach, looking for anechogenic areas in Morison’s pouch, in the perihepatic space, in the perisplenic space, in the parietal-colic showers and the Douglas cavity. Chest scans look for US signs of PNX and anechogenic areas in the pleural cavities and the pericardium. The E-FAST has good sensitivity (69–98%) and high specificity (94–100%) for free fluid detection. Its sensitivity for PNX and hemothorax is higher than that of chest X-ray, with 100% sensitivity and 98% specificity for PNX detection (71).

FALLS

Evaluation of acute circulatory failure is challenging due to the absence of a solid gold standard protocol, but the FALLS protocol can be associated with traditional hemodynamic instruments (2). This protocol (Figure 12) follows the Weil shock classification, firstly looking for obstructive shock signs (i.e., pericardial tamponade, pulmonary embolism and tension PNX), additionally investigating suggestive signs of left cardiogenic shock. At this point, the patient (defined as FALLS-responder) receives fluid therapy, and any clinical improvement suggests hypovolemic shock. The absence of improvement generates the continuation of fluid therapy, resulting in fluid overload. By elimination, this situation indicates a schematic distributional shock (i.e., septic shock) (1).

Figure 12 FALLS protocol. FALLS, fluid administration limited by lung sonography; BLUE, bedside lung ultrasound in emergency.

Obstructive shock

The probe is first applied to the heart, to exclude pericardial tamponade, immediately. Then, look for enlargement of the right heart suggestive of pulmonary embolism. The next step in the FALLS protocol is the placement of the probe in the anterior lung area, immediately ruling out a PNX, which consistently generates the A-profile of the BLUE protocol (abolished lung sliding plus an artificial horizontal repetition of the pleural line called A-lines).

Cardiogenic shock

If there are no signs of pericardial tamponade, pulmonary embolism, and PNX, then obstructive shock can be excluded and the FALLS protocol takes a step forward, looking for interstitial syndrome. On US, interstitial syndrome is characterized by the presence of pulmonary flares. Pulmonary flares are defined as three or more B-lines in a view between two ribs. B-line is a particular comet tail artifact whose properties are specified in another part of this text. According to the BLUE protocol, the detection of an interstitial, anterior, bilateral syndrome associated with lung sliding is termed profile B and is broadly equivalent to the diagnosis of acute hemodynamic pulmonary edema, with a sensitivity of 97% and 95% specificity (72,73). Pulmonary edema is associated with low cardiac output in left-sided cardiogenic shock. Left ventricular hypo-contractility is frequently associated. The absence of a B profile in a patient with acute circulatory failure schematically means that left cardiogenic shock cannot be considered.

Hypovolemic shock

If obstructive shock and left cardiogenic shock are finally excluded by applying a schematic approach, the FALLS protocol at this stage evaluates another lung artifact: the A-line. The A-profile combines the A-lines with lung scrolling (Figure 1). Faced with an A-profile, in this phase, two mechanisms of acute circulatory failure are competing: hypovolemic shock and distributive shock. In this context, distributive shock is assimilated to septic shock not only for simplicity, but also because the other causes (anaphylactic, spinal shock) are rare and clinically easy to diagnose. Profile A correlates with a pulmonary artery occlusion pressure (PAOP) equal to or less than 18 mmHg with a specificity of 93% and a positive predictive value of 97% (74). A shocked patient showing profile A at this point is called a FALLS-responder. This patient maybe needs fluid resuscitation. Fluid therapy requires rigorous monitoring of clinical circulation parameters and lung US. This step is also used to search for causal pathologies (site of bleeding, site of sepsis, etc.). The FALLS protocol defines hypovolemic shock, whatever the cause, as the improvement in circulatory function after fluid therapy (with unchanged profile A).

Distribution shock

If clinical data remain unchanged, fluid therapy will eventually create fluid overload in the tissues, particularly in the lungs. Lung flares may also appear. The transition from A-lines to B-lines during fluid therapy occurs for a PAOP value of >18 mmHg (73). Interstitial edema is an early and subclinical phase of pulmonary edema, an early indicator of fluid overload. At this point, called FALLS-endpoint, fluid therapy is stopped. It indicates that the mechanism of shock is vasoplegic, as all other causes have been excluded. At this point, fluid therapy is judged optimal and classic therapy for septic shock is started (vasoactive agents, etc.).

The main limitation of the FALLS protocol is the B profile seen on admission, which prevents PAOP evaluation. The FALLS protocol cannot be applied in this context since no endpoint can be determined.

RUSH

The RUSH exam (Figure 13) is a protocol that was developed to distinguish causes of shock using US. Given the advantages of early integration of bedside US into the diagnostic workup of the patient in shock, this protocol involves a 3-part bedside physiologic assessment (which ultimately leads to the occurrence of different types of shock), simplified as Tank, Pipe, and Pump (74). This protocol examines the pump’s anatomy of the heart cavity, the possible mechanical stresses, the cardiac contractile power, and the obstructive situation of cardiac output, such as cardiac tamponade and massive pulmonary emboli. In the Tank section, the IVC and jugular venous vein status are evaluated either in collapse or dilation, as well as retention or loss of fluids. In the Pipe section, abdominal arteries and aorta are examined for aneurysms, and the lower extremities venous system is examined for DVT. The components of the RUSH exam are heart and IVC (GDE technique), Morrison’s/FAST abdominal views, aorta, and PNX (lung US) (46).

Figure 13 RUSH protocol. HIMAP, acronym of heart, IVC, Morrison’s pouch, aorta, pulmonary; IVC, inferior vena cava; RUSH, rapid ultrasound for shock and hypotension; LVOT, left ventricular outflow tract; VTI, velocity time integral.

Conclusions

US systematic approach in critical areas provides decisive information for life-saving interventions such as cardiac arrest, shock, severe dyspnea, head-thoraco-abdominal polytrauma and supports the execution of invasive diagnostic and therapeutic procedures without expose critically ill patients to radiations (Figure 14). Moreover, US in emergency setting represents a method to assess real-time clinical status and its evolution; it reduces visit time and creates opportunities to save money, focusing on the actual clinical problem and monitoring and following the already known pathologies. US could revolutionize the field of EM in the following years, starting with some very common scenarios in ERs around the world such as dyspnea, cardiac arrest, and shock. Nevertheless, there are a few limitations: US quality is operator-dependent and subjective to interpretive error; it could also be difficult to perform in obese patients or in the presence of subcutaneous emphysema which limits the US resolution. To overcome some of these barriers, various new educational techniques have been introduced into US training: e-learning (videos, webinars and e-books); the use of low- and high-fidelity US simulators; remote supervision and tele-US, as the concept of sharing images and receiving feedback from instructors at different geographical sites may be a solution for the shortage of trainers.

Figure 14 US overview. ICP, intracranial pressure; ETT, endotracheal tube; BLUE, bedside lung ultrasound in emergency; FAST, focused assessment with sonography in trauma; US, ultrasound; RUSH, rapid ultrasound for shock and hypotension; E-FAST, extended-focused assessment with sonography in trauma; FALLS, fluid administration limited by lung sonography.

In the end, technical innovations such as elastography; contrast-enhanced ultrasound (CEUS); artificial intelligence; cloud-based POCUS functions; and augmented reality devices such as smart glasses may improve the use of US in the emergency setting (75). Our hope is that the US technique will find a place among the standard procedures useful in saving patient’s lives.

Acknowledgments

We extend our gratitude to Prof. Giovanni Volpicelli for inspiring the opening sentence of the abstract.

Footnote

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://jphe.amegroups.com/article/view/10.21037/jphe-24-5/rc

Peer Review File: Available at https://jphe.amegroups.com/article/view/10.21037/jphe-24-5/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jphe.amegroups.com/article/view/10.21037/jphe-24-5/coif). L.V. serves as an unpaid editorial board member of Journal of Public Health and Emergency from December 2023 to November 2025. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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