Introduction to Emergency U ltrasonography

john Bail itz, MD

Basem F. Khishfe, MD

Key Points

• use of ultrasound by emergency physicians has grown

significantly in the last decade.

• Emergent appl ications include the setting of trauma,

abdominal aortic aneurysm, ectopic pregnancy, gall

bladder, and kidney and as an aid to procedures (eg,

intravenous access).

INDICATIONS

Emergency ultrasound (EUS) is preformed by emergency

physicians at the patient's bedside to rapidly answer an

increasing number of focused diagnostic questions, safely

guide invasive procedures, and monitor the response to

treatment. The 2008 American College of Emergency

Physicians ultrasound guidelines describe the history and

training process for the now 11 core EUS applications. EUS

is most commonly used to evaluate and manage patients

with the following clinical presentations:

Abdominal and chest trawna. The Focused Assessment

with Sonography for Trauma (FAST) exam evaluates

for blood in the pericardial, pleural, and peritoneal

compartments in a rapid, reproducible, portable,

and noninvasive approach. The extended FAST exam

evaluates for evidence of pneumothorax.

Ectopic pregnancy. Abdominal/pelvic pain or vaginal

bleeding are common presentations in the first trimester.

An intrauterine pregnancy on EUS effectively rules out

an ectopic pregnancy in the majority of patients.

Abdominal aortic aneurysm. EUS can quickly rule

out abdominal aortic aneurysm (AAA) in patients

presenting with nonspecific abdominal or low back

pain, avoiding the need for a computed tomography

27

• The 2008 American College of Emergency Physicians

u ltrasound guideli nes describe the history and training

process for the now 11 core appl ications of emergency

ultrasound.

(CT) scan. At the other end of the clinical spectrwn, in

a hypotensive patient with abdominal or back pain, EUS

may rapidly rule in the diagnosis of AAA, facilitating

life-saving transport to the operating room instead of

threatening decompensation during CT.

Acute cholecystitis. Physical examination and laboratory

findings are often nonspecific in acute cholecystitis. EUS

often helps rule in or out the diagnosis, prompting faster

intervention or disposition.

Renal colic. In the uncomplicated patient with flank

pain and hematuria, mild to moderate hydronephrosis

often further supports the diagnosis of nephrolithiasis

without the need for additional imaging.

Procedural applications. Use of ultrasound to aid in

performing procedures includes placement of peripheral

and central lines, abscess and foreign body localization,

interspace visualization for lumbar puncture, and

US guidance of pericardiocentesis, thoracentesis, and

paracentesis.

CONTRAINDI CATIONS

Relative contraindications to EUS include patient factors

such as obesity and excessive bowel gas, as well as physician

inexperience. If the specific clinical question is not

CHAPTER 8

answered or unexpected findings are encountered, then

always proceed to the next test. EUS is another advanced

diagnostic and procedural tool, but is not always a replacement for more definitive testing.

EQUIPMENT

US is analogous to a submarine's sonar system. Sound

waves are emitted by the US probe, travel through tissue,

are reflected off structures, and then return to the probe.

Travel time is translated by the computer into depth within

the body. Strength of returning echoes is translated into

brightness or intensity of the structure on the display.

Sound is a series of repeating pressure waves. Audible

sound is in 1 6-20,000 cycle/sec or Hz range, whereas diagnostic US uses sound waves in the 2-12 MHz range (mil ­

lion cycles/ sec).

Probes send out and receive information via the piezoelectric or the pressure-electricity effect. The probe relies on

a complex, delicate, and expensive arrangement of crystals.

These crystals convert electrical energy to mechanical energy

in the form of sound waves. Returning sound waves are

translated back into electricity by the probe. Probe mainte ­

nance is of utmost importance; a probe must never be used

if cracked or otherwise significantly damaged.

Frequency. The higher the frequency of sound waves

emitted by the probe, the greater the tissue resolution, but

the lower the depth of penetration. Different types of probes

exist for different clinical questions. Low-frequency probes

(2-5 MHz) are used in thoracic and abdominal imaging to

visualize deeper structures. High-frequency probes (8--10 MHz)

are used in procedural applications, such as central line

placement and nerve blocks, to visualize more superficial

structures with more detailed resolution.

Echogenicity. Images are described in terms of echogenicity. Dense bone is highly reflective, appearing bright

or hyperechogenic. Less dense organ parenchyma appears

grainy or echogenic. Fluid-filled structures or acute bleeding do not reflect, appearing black or anechogenic. Air has

an irregular reflective surface and appears as bright scatter

with dirty posterior shadows.

Orientation. A marker on the US probe corresponds to

an indicator on the screen. By accepted standard in emergency medicine and radiology, the indicator is always on the

physician's left side of the screen. In the sagittal (longitudinal) anatomic plane, the probe marker is pointed at the

patient's head, resulting in the head being displayed toward

the left side of the screen and the feet toward the right

(Figure 8- lA). In the coronal (transverse) anatomic plane,

the probe marker is pointed at the patient's right, resulting

in the patient's right side being displayed on the left side of

the screen, similar to viewing a CT scan image (Figure 8-1B).

Modes. The most commonly used mode is the brightness (B) mode on the US machine. Other modes include

the motion (M) mode, often used to measure the fetal

heartbeat, as well as the Doppler and color flow modes to

measure blood flow.

A

8

.A Figure 8-1. A. Longitudinal probe orientation . The

probe ma rker points to the head of the patient.

B. Transverse probe orientation. The probe marker

points to the right of the patient.

PROCEDURE

The basic FAST examination consists of multiple

ultrasound views of the abdomen and lower thorax.

The patient should be in the supine position with the

physician and machine on the patient's right side of

the bed.

Subxiphoid view. The probe is placed in the subxiphoid

area with the marker in the transverse anatomic plane

aimed at the patient's left scapula. Blood between

the visceral and pleural pericardial layers will appear

anechogenic (Figure 8-2).

I NTRODUCTION TO EMERGENCY ULTRASONOGRAPHY

Figure 8-2. Subxiphoid view showing a pericardia!

effusion.

Right upper quadrant (RUQ) view. The probe is placed

in the midaxillary line in the ninth to 1 2th interspace

with the marker to the patient's head in the coronal

plane. Examine for blood in the right hemithorax,

the hepatorenal fossae (Morison's pouch), and the

inferior paracolic gutter. Morison's pouch is the most

dependent portion of the abdomen above the pelvis

and therefore the most common site to visualize

large amounts of free intraperitoneal fluid (ie, blood)

(Figure 8-3).

Left upper quadrant (LUQ) view. The probe is

placed in the posterior axillary line in the eighth to

1 1th interspace with the marker to the patient's head

in the coronal plane. Examine for blood in the left

hemithorax, the subphrenic space, the splenorenal space,

and the left inferior paracolic gutter.

Pelvic view. The probe is initially placed longitudinally

in the midline just above the pubic symphysis. Examine

for blood in the retrouterine pouch of Douglas in the

female or in the retrovesicular space in the male.

Figure 8-3. Right upper quadrant view showing

Morison's pouch between the liver and kidney. No free

fluid is present.

COMPLICATIONS

Complications may arise from inadequate visualization of

structures or image misinterpretation, but usually do not

occur because of the procedure itself.

SUGGESTED READING

American College of Emergency Physicians Emergency ultrasound guidelines. Ann Emerg Med. 2009;53:550-570.

Hoffmann R, Pohlemann T, Wippermann B, et al. Management

of sonography in blunt abdominal trauma. Unfallchirurg.

1 989;92:47 1-476.

Ma OJ, Mateer JR, Ogata M, et al. Prospective analysis of a rapid

trauma ultrasound examination performed by emergency

physicians. J Trauma. 1 995;38:879-885.

Melniker LA, Leibner E, McKenney MG, et al. Randomized controlled clinical trial of point-of-care, limited ultrasonography

for trauma in the emergency department: The first sonogra ­

phy outcomes assessment program trial. Ann Emerg Med.

2006;48:227-235.