Introduction

Ectopic pregnancy (EP) is the leading cause of maternal mortality in the United States and is estimated to have a prevalence of 8% in pregnant patients presenting to the ED for any complaint (1, 2). Indeed, the incidence of ectopic pregnancy has been rising since the mid-1980s (3). Therefore, any female of child-bearing age who comes to the emergency room with abdominal pain, vaginal bleeding, near-syncope, or syncope has ectopic pregnancy on the differential. This is a “can't miss” diagnosis. Given the volume of female patients presenting with these complaints, an algorithm incorporating first trimester ultrasound can be timesaving for the physician and patient but must increase efficiency without compromising safety.

The evaluation for ectopic pregnancy differs from other indications for bedside ultrasound. Evaluation of the uterus seeks to confirm an intrauterine pregnancy (IUP), ruling out ectopic gestation by exclusion. Visualization of the actual ectopic pregnancy is not the goal. In contrast, evaluation of the aorta, heart, and other organs typically confirms pathology (aneurysm, asystole, hydronephrosis) via direct visualization.

There are instances where an extrauterine gestation will be seen on bedside ultrasound or free fluid will be seen in a hypotensive pregnant female and ectopic pregnancy will be diagnosed or inferred. This will be the exception, however, to how bedside ultrasound is used for this application. Bedside ultrasonography instead will be used to increase the number of IUP cases that can be definitively diagnosed and discharged in the ED without further imaging.

Performing procedures on acutely ill patients can be one of the most rewarding and challenging aspects of emergency medicine and critical care practice. These patients present unique challenges to the clinician for a variety of reasons. Most notably, since they are acutely ill or decompensating, there is an urgency to perform procedures in suboptimal conditions. The patients themselves often pose unique challenges. Many patients have abnormal anatomy due to prior surgical procedures, scarring, trauma, or acute or chronic illness. In addition, obesity can obscure standard anatomic landmarks. Perhaps the clinician attempting to perform the procedure will not be the first operator or must navigate through a prior failed procedural attempt. Finally, due to the acuity of their illness, many patients do not have the functional capacity to remain in standard procedural positions (i.e., laying in Trendelenburg position or sitting upright), and this often makes successful procedural outcomes more challenging. These conditions are found in many critical care settings; therefore, the benefits of ultrasound guidance for procedures are not limited to the ED.

Any advantage over standard surface anatomy or landmark-based techniques should be a welcome addition to the arsenal of all critical care physicians. As with the diagnostic applications of ultrasound, ultrasound for procedure guidance is meant as an adjunct to the physical exam. When the sternocleidomastoid muscle cannot be seen or felt, ultrasound can help visualize the internal jugular vein and obviate the need for such landmarks.

To become versed in the language of ultrasonography, it is necessary to review some of the basic principles of physics. The wave physics principles of ordinary (i.e., audible) sound apply to ultrasound (US) and its applications. Thus, to create a foundation for further discussions, a number of definitions and basic concepts are presented here.

Basic definitions and physics principles

Amplitude is the peak pressure of the wave (Figure 1.1). When applied to ordinary sound, this term correlates with the loudness of the sound wave. When applied to ultrasound images, this term correlates with the intensity of the returning echo.

Ultrasound machines can measure the intensity (amplitude) of the returning echo; analysis of this information affects the brightness of the echo displayed on the screen. Strong returning echoes translate into a bright or white dot on the screen (known as hyperechoic). Weak returning echoes translate into a black dot on the screen (known as hypoechoic or anechoic). The “gray scale” of diagnostic ultrasonography is the range of echo strength as it correlates to colors on a black–white continuum (Figure 1.2).

Velocity is defined as the speed of the wave. It is constant in a given medium and is calculated to be 1,540 m/s in soft tissue (i.e., the propagation speed of soft tissue is 1,540 m/s). Using this principle, an ultrasound machine can calculate the distance/depth of a structure by measuring the time it takes for an emitted ultrasound beam to be reflected back to the source (Figure 1.3).

Introduction

Chest ultrasound is reviewed for a variety of applications throughout this book. Literature to support its use in the diagnosis of pneumothorax, hemothorax, and nontraumatic pleural effusions is provided. Indeed, this literature lends support to the superiority of ultrasound as a diagnostic modality over chest x-ray for many applications. In addition, the patient safety benefits of ultrasound when performing procedures such as thoracentesis are presented.

Not surprisingly, there is more. With increased use of chest ultrasound in the intensive care unit setting has come a wider range of applications for its use. The role of chest ultrasound in the diagnosis of pulmonary edema or extravascular lung water (EVLW) is reviewed in this chapter. More important, the terminology that has been developed by pioneers in thoracic ultrasound and the concepts behind it are described because they are crucial to the diagnostic use of chest ultrasound for all chest applications.

The two most basic concepts – A lines and B lines – are described. For more detailed descriptions of these and other chest ultrasound applications, sonographers are encouraged to read Dr. Daniel A. Lichtenstein's book, General Ultrasound in the Critically Ill (1).

Focused questions for chest ultrasound

The questions for chest ultrasound are as follows:

1. Are A lines present?

2. Are B lines present?

Anatomy

When using ultrasound to make diagnoses in lung pathology, it is important to recall some of the basic principles described in Chapter 1.

Introduction

Ultrasound (US) was first used in the evaluation of trauma patients in Europe in the 1970s. The German surgery board has required certification in ultrasound skills since 1988. Since the mid-1980s in the United States, the use of ultrasound in trauma has become more widespread and has all but replaced diagnostic peritoneal lavage (DPL) in most trauma centers. The FAST exam has been included as part of the advanced trauma life support course since 1997 (1). In addition, the American College of Surgeons has included ultrasound as one of several “new technologies” that surgical residents must be exposed to in their curriculum. Both the American College of Emergency Physicians and the Society for Academic Emergency Medicine support the use of ultrasound to evaluate blunt abdominal trauma as well. Since 2001, training in emergency ultrasound has been required for all emergency medicine residents (2, 3 and 4). All physicians who will be evaluating trauma patients must become proficient in the use of trauma ultrasound.

The objective of the FAST exam is to detect free intraperitoneal and pericardial fluid in the setting of trauma. The cardiac windows are especially critical in penetrating trauma and are reviewed in this section and in Chapter 3. In advanced applications of the FAST exam, pleural fluid and other signs of thoracic injury can be assessed as well.

Cannulation of the brachial and cephalic veins of the upper extremity

Peripheral venous cannulation can sometimes be unsuccessful after multiple attempts – even with attempts at the relatively larger antecubital veins. In this case, one might consider attempting cannulation of the brachial or cephalic veins. These veins lie deeper in the structures of the upper arm and are not readily palpable. Consequently, these veins are not generally used for intravenous catheter placement in the absence of ultrasound guidance. In most patients, the depth of these vessels requires that a longer intravenous catheter (1.75–2.0 in) be used. Caution should be exercised with the more proximal brachial vein because it lies immediately adjacent to the ulnar and median nerves.

Focused question

1. Where is the target vein?

Anatomy

The axillary vein divides into the cephalic vein, which runs superficially toward the lateral (dorsal) aspect of the upper arm; the basilic vein, which courses superficially along the inferior and medial (ventral) aspect of the arm; and the brachial vein, which runs deeply inferior to the biceps muscle (Figure 13.1). The basilic and cephalic veins rejoin in the antecubital fossa, and the brachial vein runs deep in this location. Frequently, the brachial vein will be found as paired superficial and deep brachial veins.

Technique

Probe selection

Generally, a high-frequency linear transducer is used.

Special equipment

For deep vein cannulation, a longer catheter is required (at least 2 in). Sterile probe covers (described in Chapter 12) can be used for sterile peripheral access.

Introduction

The kidney and bladder are two of the most sonographically accessible organs. The evidence for using ultrasound to make lifesaving diagnoses in this application is not as apparent as it is for cardiac or aortic ultrasound (except, of course, if flank pain and hydronephrosis are the result of a rapidly expanding AAA – see Chapter 5). Indeed, it is accurate to say that CT is dramatically more sensitive and specific in detecting ureteral stones and that ultrasound has a very low specificity for identifying ureteral stones (1–4). However, despite the advantages of CT for nephrolithiasis, there is still a role for ultrasound in evaluating the urinary tract in the emergency setting. In the most straightforward case, US identification of mild or moderate unilateral hydronephrosis in a patient with known renal colic and normal renal function testing (and a normal aortic screening evaluation) can obviate further radiologic testing. Patients who have relative contraindications to radiation exposure (pregnancy, pediatric patients) can also have ureteral obstruction evaluated by ultrasound. Renal ultrasonography easily and rapidly obtains evidence for or against high-grade obstruction, thereby expediting decisions regarding management and disposition (5, 6).

In addition, determination of bladder volume is another important indication for urinary tract ultrasound. Before catheterizing a patient to evaluate for postrenal obstruction or urinary retention secondary to neurologic events, an ultrasound can give an estimation of bladder volume and indicate whether catheterization is even necessary. Pediatric patients can also have bladder volume evaluated with ultrasound.

Introduction

One of the most exciting applications for bedside ultrasound is echocardiography. Differentiating between pulseless electrical activity (PEA) and asystole in patients with no pulse, identifying pericardial effusions in hypotensive patients, and estimating volume status or global cardiac function in hypotensive patients are all applications for bedside echocardiography that can make a difference in patient treatment and outcome. However, it is important to note that this manual is not meant to teach a noncardiologist to be an echocardiographer. Bedside echocardiography is a tool to be used by clinical practitioners who need quick answers to specific questions about cardiac function in critically ill patients. Any good physician must recognize the limitations of his or her knowledge and skill; in cases where ambiguity remains after bedside ultrasonography, follow-up testing should be consistent with normal practice patterns (1).

This chapter also reviews how to make estimations of global cardiac function and how to perform estimations of volume status by evaluating inferior vena cava (IVC) respiratory variation and collapse. Finally, images of a dilated right ventricle are reviewed so that in appropriate clinical settings, support for the diagnosis of pulmonary embolus can be made.

Echocardiography is essential in looking for wall motion abnormalities in ischemic heart disease and in evaluating valvular cardiac disease, but these applications can be complicated and require more extensive training. Again, knowing the limitations of bedside ultrasonography is essential for practicing safely.

Introduction

Ocular ultrasound as used by the emergency or critical care physician has several applications. The diagnosis of lens disruption and/or retinal detachment can be made with ultrasound and has been well described in the ophthalmology and radiology literature (1, 2). Ultrasound can also diagnose the presence of ocular foreign bodies (1, 2). However, more recently, other research focuses for ocular ultrasound have included the use of ultrasound to measure the optic nerve sheath diameter. Here, the concept is based on the idea that increased intracranial pressure (ICP) is reflected through the nerve sheath, causing edema and swelling. Since increases in ICP are transmitted by the cerebrospinal fluid (CSF) down the perineural subarachnoid space of the optic nerve, this expansion of the nerve sheath that can be measured by ultrasound (3–5). In many ways, this technique parallels the concept of papilledema as a marker for increased ICP. However, optic nerve ultrasonography is arguably easier to perform and more quantifiable than the presence or absence of papilledema. It is this interest in ultrasound's potential to measure ICP noninvasively that has sparked so much research.

Many ocular ultrasound studies have been done to try to define normal optic nerve diameter ranges and where enlargement becomes pathologic and correlates with increased ICP. Although research is ongoing, to date most researchers have found that both pediatric and adult ocular nerve sheath diameters >5 mm have correlated with evidence of increased ICP as measured by degree of hydrocephalus, intrathecal infusions where lumbar pressures were measured, or CT evidence of increased ICP (6–9).

Introduction

With the possible exception of pericardial tamponade, there is no other condition in which the special capabilities of bedside sonography are of such striking benefit (1, 2). Emergency bedside ultrasonography enables the emergency physician to confirm a high-risk diagnosis – decreasing the time needed to mobilize resources – or even transfer the patient to a referral center if necessary. This one exam will save lives if incorporated into the regular practice of emergency physicians and other critical care physicians involved in the evaluation of acutely ill patients (1).

Part of the reason for this is because abdominal aortic aneurysms (AAAs) can present with such varied symptoms. Patients can have back pain, flank pain that sounds like ureteral colic, syncope, abdominal pain, gastrointestinal bleeding, or any variety of these. Because of this and because of the ease of a screening abdominal aortic ultrasound, it is recommended that all patients with the aforementioned presenting symptoms and risk factors for AAA undergo an ultrasound screening exam. This is particularly true if a patient with flank pain is found to have unilateral hydronephrosis. An expanding abdominal aneurysm can compress the ureter so hydronephrosis results. It is far better to do extra screening exams in at-risk patients with flank pain, than to miss this life-threatening diagnosis.

Focused questions for aortic ultrasound

The focused questions for aorta ultrasound are as follows:

1. Is the abdominal aorta >3 cm in diameter?

2. Are the ileac arteries >1.5 cm in diameter?

Introduction

Vascular access is one of the most basic required skills of the critical care physician. Many factors – including body habitus, volume depletion, shock, history of intravenous drug abuse, prior cannulation, scarring, thromboses, congenital deformity, and cardiac arrest – can make it difficult to obtain vascular access in patients who are critically ill or injured. Traditionally, surface anatomy and anatomic landmarks have served as the only guides for locating central veins. The incorporation of ultrasound into the procedure allows for more precise assessment of vein and artery location, vessel patency, and real-time visualization of needle placement.

The paradigm for radiology is to perform invasive procedures such as vascular access under real-time direct visualization so as to reduce complications. Although patients may have complicating medical problems, those scheduled for procedures in radiology are usually hemodynamically stable. Why then would critical care physicians perform invasive procedures on more unstable patients without the same tools and techniques to increase safety?

Real-time bedside ultrasonography facilitates rapid and successful vascular access (1–6). Indeed, there is increasing institutional and literature support for performing cannulation under direct visualization as the technology spreads throughout the hospital. This is not limited to the ED but is applicable to any critical care unit or patient care area in the hospital.

Focused questions for vascular access

The questions for vascular access are as follows:

1. Where is the target vein?

2. Is it patent?

This chapter covers techniques to make this assessment seem second nature.

Introduction

Although long bone fractures are often detected clinically, the sensitivity of the physical exam is insufficient to exclude pathology. In addition, the management of fractures varies considerably based on characteristics undetectable by physical exam alone (displacement, angulation, comminution). Thus, clinicians often rely on plain x-ray (as well as CT and MRI) to characterize fractures in patients with extremity trauma.

The role that ultrasound may play in the evaluation of orthopedic injuries is threefold. First, in a select group of injuries, diagnosis and treatment may be more rapid by using ultrasound over other modalities. There is some evidence that ultrasound is superior to plain x-ray in select fractures (sternal, rib) (1–3). In addition, there are some clinical scenarios where bedside diagnoses can expedite traction, anesthesia, and other maneuvers such as alignment through closed reduction (4, 5). Second, imaging modalities are not always rapidly available. In some emergency departments, even plain x-rays take a significant amount of time to be performed. In austere environments (developing nations, remote areas), portable bedside ultrasound technology may be all that is available, given the setup costs and bulk of x-ray, CT, and MRI machines. Finally, radiation is relatively contraindicated in some patients, such as children or the elderly. Radiation exposure can be minimized using ultrasound as an alternative diagnostic tool.

Focused questions for bone ultrasound

The questions for bone ultrasound are as follows:

1. Is there an interruption in the bony cortex?

2. Can a degree of angulation or displacement be assessed?

Introduction

Gallbladder disease is well suited for emergency ultrasound investigations. Use of diagnostic ultrasound frequently leads to either confirmation of a presumptive diagnosis or rapid narrowing of the differential diagnoses. However, if biliary ultrasound findings are equivocal or conflict with initial clinical impressions, the emergency physician should be reminded that formal studies or other imaging modalities may be complementary.

In this section, the application of bedside ultrasonography in the evaluation of the gallbladder is discussed.

Focused questions for gallbladder ultrasound

As with all emergency bedside ultrasound, it is important to remember the focused questions you are trying to answer with your ultrasound. In gallbladder ultrasound, these questions are as follows:

1. Are there gallstones?

2. Does the patient have a sonographic Murphy sign?

It is also useful to know the following:

1. Is the common bile duct dilated?

2. Is the anterior wall thickened?

3. Is there pericholecystic fluid?

However, the first two questions are far and away the most helpful and diagnostic (1, 2).

Anatomy

It is important to remember that the gallbladder is not a fixed organ, so it can move to a variety of locations in the right upper quadrant (Figure 7.1). The gallbladder neck does have a fixed relationship to the main lobar fissure and the portal vein. The main lobar fissure connects the right portal vein to the gallbladder neck, and the fissure can be traced between the two (Figure 7.2). Another anatomic relationship that is reliable is that the bile duct is always anterior to the portal vein.

Introduction

Although not one of the original six American College of Emergency Physicians indicated exams, evaluation for deep vein thrombosis (DVT) is one of the most useful exams for critical care physicians. There are approximately 250,000 new diagnoses of DVT per year and 50,000 deaths from thromboembolic disease annually (1, 2). The estimated rate of propagation from DVT to pulmonary embolism ranges from 10% to 50% (1, 2). Because the incidence of DVT is so high and because this disease is so prevalent in critical and acute care settings, the ability to rule in or rule out DVT at the bedside is a particularly powerful tool. The simplified compression technique described in this chapter evaluates for DVT at two anatomic sites of the lower extremity venous system. This protocol has been evaluated in multiple randomized controlled studies and has become a well-accepted protocol used for decision making in conjunction with clinical pre-test probability assessments (3–12).

Focused questions for DVT ultrasound

The questions for DVT ultrasound are as follows:

1. Does the common femoral vein fully compress?

2. Does the popliteal vein fully compress?

Anatomy

The anatomy of the lower extremity should be reviewed so the DVT compression ultrasound exam can be done properly. The ileac vein becomes the common femoral vein (CFV) as it leaves the pelvis. The most proximal tributary of the CFV is the greater saphenous vein (GSV) (Figure 8.1).