Ultrasound 2: Emergency Ultrasound Techniques Portal
Bedside ultrasound has become an essential component of emergency medicine. This portal discusses the most useful exams in acute patient care. Although an initial time investment is required to become adept at ultrasound, once mastered, ultrasound examination can become an indispensable tool in the clinician’s practice.
Ultrasound in Trauma: The FAST Exam
The
purpose of the Focused Assessment of Sonography in Trauma (FAST) exam
is to identify free fluid (usually blood) in the pericardial, pleural,
or intraperitoneal spaces. As such, the FAST exam is simply a search
for free fluid around the edges of the heart, diaphragm, liver, spleen,
and bladder. Learning to interpret the FAST exam involves learning
where free fluid commonly collects adjacent to these organs. The FAST
exam is usually performed with the patient in the supine position. Free
fluid is jet black and tends to collect in the most dependent areas and
surround the organs. The FAST exam is often broadened to include views
of the thorax to assess for pneumothorax and hemothorax. This approach
has been named the EFAST, or extended FAST, exam.
A standard medium frequency curved array probe is typically employed (Figure 1), but a lower frequency probe with a smaller footprint may be more useful in obese patients (Figure 2). By convention, when performing abdominal sonographic exams, the probe marker-dot correlates with the left side of the ultrasound image. When performing cardiac ultrasound, however, the marker-dot correlates with the right side of the image. The easiest way to avoid being confused by the probe marker-dot and image marker-dot is to understand the shape of the sonographic plane associated with each probe and to practice reproducing standard images. If anatomic structures are arranged in the standard fashion on any given image, the position of the marker-dot is irrelevant. Touching one side of the probe while looking at the ultrasound image may help with probe marker orientation.
 |  |
Cardiac Views
Two different
cardiac views can be performed with the FAST exam. One of the two is
usually sufficient to evaluate for a clinically significant pericardial
effusion. It is important to learn both views because in any given
patient one of the views may be easily obtained and the other
impossible to obtain.
Subxiphoid Four-Chamber View: Place the probe in the subxiphoid region with the marker-dot toward the patient’s right side or right shoulder (Figure 3). Angle the probe toward the left shoulder. This view uses the left lobe of the liver and a pericardial effusion (if present) may be seen between the liver and the heart. Increasing the depth of the image and having the patient take a deep breath improves chances of obtaining a good image. The liver is visualized at the top of the screen with the heart just beneath it (Figure 4). Pericardial fluid appears as a hypoechoic rim between the myocardium and pericardium. Clotted blood in the pericardium may also be visualized and is slightly more hyperechoic than fluid (Figure 5).
 |  |
Parasternal Long-Axis View: Place the probe just to the left of the sternum in about the 4th or 5th intercostal space with the marker-dot toward the 4 o’clock position (Figure 6). This view allows a good look at the anterior and the posterior pericardium. Sliding the probe toward the cardiac apex (toward the 4 o’clock position) provides a good look at the apex (Figure 7). This view requires less depth and is easier to obtain in uncooperative patients.
 |  |
Abdominal and Lower Thoracic Views
When
a patient is in the supine position, the most dependent area in the
upper peritoneum is Morison's pouch (potential space between liver and
kidney) and the most dependent area in the lower peritoneum is the
retrovesicular space (potential space posterior to the bladder) in the
male and the pouch of Douglas (the extension of the peritoneal cavity
between the rectum and back wall of the uterus) in the female.
Right
Coronal and Intercostal Oblique Views: The easiest abdominal view to
obtain is the right upper quadrant view. To obtain this view, place the
probe in the mid-axillary line at about the 8th to 11th intercostal
space with the marker-dot pointed cephalad (Figure 8). This gives a
coronal view of Morison’s pouch (Figure 9). Free fluid is usually seen
in Morison’s pouch (Figure 10), along the lower edge of the liver or
around the lower tip of the liver, so it is important to follow the
lower edge of the liver caudally until a good view of the tip is
obtained (Figure 11). Rib shadows may be prominent when the marker-dot
is pointed directly cephalad. Shadows can be minimized by rotating the
cephalad portion of the probe slightly toward the belly, so that the
marker-dot is pointed toward the posterior axilla. From this position,
simply slide the probe cephalad to obtain a view of the diaphragm and
look for pleural fluid. Pleural fluid appears as a jet-black triangle
just superior to the diaphragm. Also, this view may reveal free
intraperitoneal fluid superior to the liver, between the liver and the
diaphragm.
 |  |
 |  |
Left Coronal and Intercostal Oblique Views: This abdominal view is the most difficult to obtain. Place the probe in the posterior axillary line at about the 6th to 9th intercostal space with the marker-dot pointed cephalad (Figure 12). From this position the interface between the spleen and left kidney can be found. To eliminate rib shadows and to obtain a better view of the spleen, slide the probe cephalad and again rotate the cephalad portion of the probe toward the bed, so that the spleen (not the kidney) is seen (Figure 13). Free fluid is rarely seen between the spleen and the kidney but rather surrounding all other parts of the spleen (Figure 14). The marker-dot is pointed toward the posterior axilla. This view allows good images of the lower tip and superior surface of the spleen, where intraperitoneal free fluid is most likely to collect. The diaphragm is also seen in this view, just superior to the spleen. A pleural effusion or hemothorax appears as a jet-black triangle just superior to the diaphragm (Figure 15).
 |  |
 |  |
Pelvic Views: Pelvic views are not as easy to obtain as right upper quadrant views, but since the pelvis is the most dependent part of the intraperitoneal space, it is the most likely place in which to see abdominal free fluid. Obtain both longitudinal and transverse views of the pelvis. Perform the longitudinal view first, as this makes understanding the anatomy and obtaining good images easier. Place the probe in the midline just superior to the pubic bone with the marker-dot pointed cephalad (Figure 16). Make sure the probe position is correct by actually pressing it on the pubic bone and noting a bone shadow on the image. From this position, sliding the probe slightly cephalad produces a good longitudinal pelvic view. The bladder is found just cephalad to the pubic bone and can usually be found even if it is nearly empty. A full bladder is triangular and the lower angle marks the border between the intraperitoneal space (left side of the image) and the true pelvic structures (right side of the image) (Figure 17). In a male, free fluid is seen on the left side of the image, posterior to the wall of the bladder (Figure 18). In a female, the body of the uterus sits in the intraperitoneal space just posterior to the bladder, so free fluid is seen just posterior to the uterus (the pouch of Douglas, Figures 19 and 20). In a male, if the bladder is empty, it is difficult to recognize pelvic free fluid. In a female, the pouch of Douglas may still be identifiable, even when the bladder is empty. To obtain transverse views, simply rotate the probe 90 degrees, pointing the probe marker to the patient’s right side.
 |  |
 |  |
Anterior Thoracic Views
When using ultrasound to
evaluate for a pneumothorax, place the probe on the anterior chest in
the 3rd to 4th intercostal space in the midclavicular line (Figure 21).
This is a starting point and a likely place to find a pneumothorax when
the patient is in the supine position. Subsequent imaging can be done
on any part of the chest wall if there is concern for a small or
loculated pneumothorax.
A high frequency vascular/small parts probe can be used for this exam, but a standard curvilinear abdominal probe works well also. The most important part about this exam is decreasing the depth setting, so that the ultrasound image shows a maximum depth of about 4 cm. Place the probe in a longitudinal position with the marker-dot pointed cephalad. In this orientation, rib shadows can be used to find the pleural plane (Figure 22). It is best to adjust the probe linearly until two ribs are apparent, one on each side of the image. Between the ribs, the pleural interface is apparent at the posterior border of the ribs. With respirations, a sliding movement becomes apparent along the pleural line. Lack of movement indicates a pneumothorax. It is important to anchor the probe and hold it very still while looking for the sliding motion of the visceral pleura against the perietal pleura. Comparing one side of the chest to the other is usually helpful when deciding if a pneumothorax exists.
 |  |
The Aorta
An abbreviated examination of the distal
aorta is usually easy to complete in less than 1 to 2 minutes. Ideally,
evaluate the entire length of the abdominal aorta (AA) from the
diaphragm to the bifurcation in both the longitudinal and transverse
planes. Examine patients in the supine position. Bowel gas is the most
common cause for inability to view the AA, and a better view may be
obtained by turning the patient to either side.
Since no ribs or other bony structures overlie the AA, a variety of probes can be used for the exam, from curvilinear transducers with large footprints (Figure 1) to small-phased array probes typically designed for echocardiography (Figure 2). By convention, the AA is imaged in the longitudinal (sagittal) plane by pointing the probe marker-dot toward the patient’s head. In the transverse (axial) plane, point the probe marker-dot toward the patient’s right side. Select a sufficient depth at the beginning of the exam until you identify the AA.
Two primary obstacles to obtaining adequate images of the AA are bowel gas and obesity. Bowel gas may force the examiner to move the probe slightly to either side of the midline to acquire views. Another option is to press firmly in order to compress the bowel with the transducer and move bowel gas away from the area of interest.
If time permits, for a complete exam of the AA, place the transducer initially just caudal to the xiphoid process (Figure 23). In the transverse plane, the spine is an excellent point of reference. The spine appears as a posteriorly oriented concave structure, which is highly reflective (hyperechoic) and casts a shadow. The AA is easily found immediately anterior and slightly to the left of the spine. It is pulsatile with a round to ovular shape (Figure 24). This usually makes it easy to differentiate from the inferior vena cava (IVC), which is thin-walled, varies in size with respiration, and is often flattened by minimal pressure from the transducer.
 |  |
As
the transducer is angled more caudal, branches of the AA come into view
starting with the celiac trunk and then the superior mesenteric artery
(SMA). The latter is in close proximity to several other vascular
structures in the transverse plane. In the longitudinal plane at the
xiphoid process, the examiner can angle the probe beam from right to
left to image the proximal IVC and AA (Figure 25). Again, these
structures can be differentiated by wall thickness, pulsatile motion,
and variation in size with respiration. Many examiners utilize a sniff
test to help with differentiation of these structures as well. Having
the patient quickly sniff creates a sudden drop in thoracic pressure,
which pulls blood from the IVC into the thorax and causes the structure
to collapse. In addition, the IVC is often seen directly entering the
right atrium of the heart (Figure 26) while the AA will demonstrate the
celiac trunk and SMA exiting from its anterior surface (Figure 27).
The majority of abdominal aortic aneurysms (AAAs) are located at the distal AA. In unstable patients, examiners may opt to examine the distal aorta more directly first. The distal aorta is best viewed by placing the transducer just superior to the umbilicus in either the longitudinal or transverse plane (Figures 28 and 29). The longitudinal plane is often initially performed to locate the AA and search for saccular AAA or vascular wall blebs. To the novice, it is surprisingly close to the anterior surface in thin patients due to the lumbar curvature of the spine (Figure 30). Measurements of the anterior-posterior (AP) and lateral diameter from outer wall to outer wall in transverse section provide the most accurate data of the external diameter of the AA (Figure 31). In general, ultrasonic images in patients with a large AAA are immediately positive, but visualization of the entire length of AA is required to exclude AAA. Should its diameter be adequately visualized and appear normal over this length, then this excludes a ruptured AAA with an essentially 100% negative predictive value.
Aneurysm
The
primary abnormality that the physician seeks is aneurysmal enlargement
of the AA. This is most commonly visualized in the transverse view as
an aorta greater than 3.0 cm in diameter (Figure 32). Aneurysmal
dilation is usually fusiform, resulting in a uniform symmetric
concentric enlargement of the circumference. Turbulent blood flow is
often seen within the lumen (Figure 33). Localized out-pouching of a
segment of the aortic wall results in the more unusual saccular
aneurysm formation. Aneurysmal dilatation is usually most often
confined to the infrarenal aorta and usually terminates proximal to the
bifurcation. Contiguous thoracoabdominal aneurysms occur in a minority
of cases and involve the thoracic aorta in addition to the AA,
including the segment involving the celiac, superior mesenteric, and
renal arteries. The iliac arteries are involved in 40% of patients with
AAA,1 and occasionally, iliac artery aneurysms occur in an isolated
fashion. More than 90% of AAAs occur in the distal AA, below the renal
arteries.2 Rarely, an AAA may be detected only in the proximal AA.
Intraluminal Thrombus
With increasing diameter, the
laminar flow rate decreases at the periphery, resulting in blood
stagnation and thrombus formation. This intraluminal thrombus is well
visualized by ultrasound and is more common anterior and laterally but
may be circumferential (Figure 34). Thrombus is found in both ruptured
and non-ruptured AAAs. It is not an indication of rupture or
dissection, and is not a false lumen. Take care to measure from outer
wall to outer wall of the aorta, to avoid falsely excluding an
intraluminal thrombus.
Hemoperitoneum
Rupture into the
peritoneal cavity may present with acute hemoperitoneum that may be
visualized with the right intercostal oblique window of the FAST
examination or other windows. Perform a FAST exam on any patient with
suspected rupture of an AAA.
The Cardiac Exam
Four common
probe positions, or views, are used for bedside
echocardiography.
It is important to learn how to obtain all of the common
echocardiograph views. For ideal positioning, have the patient in the
left lateral semi-decubitus position, although this may not be possible
in the emergent setting. Also, depending on a patient’s body habitus
and comorbidities, it is impossible to estimate which view will provide
the best information. For cardiac studies, use either a curved linear
array probe or a phased array sector probe with median frequencies of
3.5 MHz (2.5 to 5.0 MHz) (Figure 2).
Beginners often find echocardiography difficult to learn because of the complex anatomy of the heart and difficulty obtaining standard images. Part of this difficulty stems from confusion over marker-dot orientation on the display of the cardiac presets, which are reversed from the abdominal exam presets. Also, probe alignment, tilt, and rotation can be initially frustrating to learn. One way to avoid these frustrations is to focus on learning what the standard images look like and to aim to reproduce these standard images during each practice exam.3
When sonographers get accustomed to looking at images in the standard orientation, they will immediately recognize if the image is backward on the monitor and rotate the probe 180 degrees to correct it. This approach makes the marker-dot orientation almost irrelevant.
Subcostal View
The
subcostal view may be the easiest to obtain in a critically ill patient
who is in the supine position. Place the probe in the subcostal
location with the probe marker-dot pointed to the patient’s left side
(Figure 35). Aim the probe toward the left shoulder at an acute angle
to the patient’s abdomen. The standard subcostal view uses the left
lobe of the liver as an acoustic window (Figure 36). In this view, the
right ventricle (RV) lies directly posterior and adjacent to the left
lobe of the liver. The left ventricle (LV) is seen posterior to the RV
in this view. The apex of the heart is oriented toward the right side
of the screen.
Parasternal Long-Axis View
The parasternal
long-axis view is the second view that is usually easy to obtain when a
patient is in the supine position. Place the probe just left of the
sternum in the 3rd, 4th, or 5th intercostal space (Figure 37). Aim the
marker-dot on the probe toward the patient's right shoulder. In the
standard parasternal long-axis view, the LV is on the left side of the
monitor (Figure 38). The RV is at the top of the screen and is usually
not very prominent. The base of the LV, the mitral valve, left atrium,
aortic valve, and proximal aorta are also seen. The apex of the LV is
not visualized in the standard view. The aortic valve and root should
be on the right side of the screen. The bottom-most structures on the
standard view should be the inferior wall of the LV, the mitral valve,
and the left atrium.
Parasternal Short-Axis View
By
simply rotating the probe 90 degrees from the parasternal long-axis
view and aiming the marker-dot toward the left shoulder, you can obtain
the parasternal short-axis views (Figure 39). The parasternal short
axis provides cross-sectional views of the heart. By tilting the probe
toward the base or toward the apex of the heart, you can obtain three
very different views (Figure 40). The first short-axis view is at the
base of the heart, at the level of the aortic valve (Figure 41). The RV
is at the top of the screen, the right atrium at the left of the
screen, and the left atrium is the bottom-most structure. The aortic
valve should be in the center of the screen, the cross-section showing
the three cusps. As the probe is tilted toward the apex of the heart,
short-axis views through the mitral valve and just below the mitral
valve at the level of the papillary muscles can be obtained. The
short-axis view through the mitral valve shows the RV at the top of the
screen and the LV cross-section containing the anterior and posterior
leaflets of the mitral valve toward the bottom of the screen (Figure
42). At the apex of the heart, you see a cross-section through the LV
papillary muscles toward the right and bottom of the screen, with the
RV again at the top of the screen (Figure 43).
Apical View
The
last standard view is the apical view. It is usually necessary to have
the patient lying in the left lateral decubitus position in order to
obtain good apical views. The easiest apical view to obtain is the
4-chamber view. To obtain this view, place the probe at the point of
maximal impulse (PMI) with the marker-dot aimed toward the patient’s
left posterior axilla (Figure 44). The probe should be at the apex of
the LV and directed toward the base of the heart, which is usually
toward the patient's right shoulder. The standard view in this position
shows the apex of the heart toward the top of the monitor. The left
side of the heart is on the right side of the image and the right side
of the heart is on the left side of the image (Figure 45).
Novices
should learn to recognize the standard echocardiographic images and
concentrate on trying to reproduce standard images when practicing the
exam. Using this approach avoids confusion about which direction the
probe or the marker-dot should be pointed, and it is relatively easy to
master the primary applications of cardiac ultrasound.
Evaluation of the Inferior Vena Cava
The
evaluation of the IVC with bedside ultrasound is a rapid and
non-invasive method to obtain an estimation of the central venous
pressure (CVP) in a hypotensive patient. Place the probe in the
subcostal space with the marker-dot pointed toward the patient’s feet
(Figure 46). This view shows the left lobe of the liver, right atrium
and RV, IVC, and hepatic veins. Measure the proximal IVC about 2 to 3
cm distal to the right atrium, at the entry of the hepatic vein (Figure
47). The AP diameter of the proximal IVC usually measures about 1.5 to
2.0 cm during expiration and collapses with inspiration. The AP
diameter of the proximal IVC usually collapses more than 50% when the
patient sniffs or during forceful inhalation. If it collapses less than
50%, then right-sided filling pressure and CVP are elevated.3
Pelvic Ultrasound
Transabdominal
and transvaginal sonography are complementary imaging techniques that
should be used together. In general, do not perform transvaginal
imaging without also performing a transabdominal scan. Transvaginal
imaging allows the probe tip to be placed close to the organ of
interest; high-frequency probes can be used to generate high-resolution
images. However, transvaginal probes have a limited field of view and
objects more than a few centimeters away from the probe tip may not be
seen. Transabdominal sonography uses lower-frequency probes so the
field of view is much larger and provides better overview of pelvic
structures. The main drawback of transabdominal scanning is that the
resolution is lower, so details of small pelvic structures are not
discernible, particularly ovaries and early pregnancies.
Transabdominal Scanning
Transabdominal
scanning is usually accomplished using a 3.5 to 5 MHz curvilinear
ultrasound probe (Figure 1). The bladder is used as a window in
transabdominal scanning, so the patient’s bladder should be full to
obtain optimal images. In the emergency setting, transabdominal
scanning is often done without a full bladder because it is not
practical to have patients drink fluid and wait for an hour while their
bladders fill. Quality images are usually obtained without bladder
filling in thin women and those with an anteflexed uterus.
Gentle
pressure on the probe can also be used to produce good quality
transabdominal images without filling the bladder.
The best transabdominal view for evaluating the uterus and its contents is the standard midline sagittal view (Figure 48). To obtain this view, place the probe on the abdominal wall in the midline just above the pubic bone, with the marker-dot pointing cephalad (Figure 49). By convention, the marker-dot on the probe should correlate with the left side of the monitor so that in sagittal images cephalad structures are on the left side. This view provides a longitudinal image of the uterus and the entire midline stripe should be visible (Figure 50). The cervix is seen just posterior to the bladder angle with the body of the uterus to the left of the angle and the vaginal stripe to the right. The ovaries can be seen by sliding the probe laterally (with the marker-dot still pointing cephalad) and aiming the beam toward the contralateral adnexa, using the bladder as a window. Sometimes when the bladder is very full or a large pelvic mass is present, better images can be obtained by placing the probe directly over the adnexa.
 |  |
It may be easier to visualize the ovaries and other adnexal
structures with the standard transabdominal transverse view (Figure
51). Obtain this view by placing the probe in the midline of the
abdominal wall just above the pubic bone, with the marker-dot pointing
to the patient’s right side (Figure 52). This view provides a
transverse image of the uterus and allows the midline of the uterus and
the adjacent adnexa to be seen in the same image (Figure 53). In
transverse images, anatomic structures have the same orientation as on
a CT scan: right-sided structures are on the left side of the monitor
and left-sided structures are on the right. To examine the entire
pelvis in transverse planes, keep the probe in the midline suprapubic
region with the marker-dot pointed to the patient’s right and aim the
beam caudad and cephalad. This motion allows the uterus to be viewed in
transverse sections from the cervix to the fundus, respectively.
 |  |
The ovaries are most commonly found between the body of the uterus and the pelvic sidewall. In their normal location, the ovaries are bound posteriorly by the internal iliac artery and superiorly by the external iliac vein. These vessels can be identified and used to help locate the ovaries. Normal ovaries appear as small discrete hypoechoic structures. Individual ovarian follicles are usually not visible with transabdominal imaging. Normal ovaries are not always seen with transabdominal sonography because they are relatively small and may be camouflaged by bowel or other surrounding structures with similar echogenicity. However, adnexal masses are often larger and easy to identify with transabdominal imaging.
Transvaginal Sonography
Transvaginal
scanning is different from other ultrasound techniques because the
ultrasound probe is placed inside the vagina and very close to the
organs of interest. Transvaginal sonography is accomplished using a
specialized probe with a 5 to 7.5 MHz transducer (Figure 54). The probe
has a marker-dot, similar to other ultrasound probes, which correlates
with the left side of the monitor screen.
Before the transvaginal probe is used, it must be thoroughly cleansed and covered by a rubber or vinyl sheath. Place conducting gel inside the sheath before the probe is covered to eliminate air bubbles in the tip of the sheath. Use water-based lubricant (not conducting gel) to lubricate the outside of the sheath before insertion into the vagina. Ultrasound conducting gel may be irritating to the vaginal mucosa.
Patients should empty their bladder before transvaginal scanning is performed. A full bladder straightens the angle between the uterus and vagina and moves the body of the uterus away from the probe. Patient positioning is important in obtaining good transvaginal scans. The operator must be able to aim the probe anterior enough to see the fundus of an anteverted uterus. Scanning is best accomplished while the patient is in lithotomy stirrups or by elevating her pelvis on a pillow while she is in a frog-leg position. Many clinicians prefer to use lithotomy stirrups and perform transvaginal sonography as part of their pelvic examination, after the speculum and bimanual examinations.
Before inserting the transvaginal probe, explain to the patient that transvaginal sonography is similar to the bimanual pelvic exam but that visual rather than tactile information is obtained. Transvaginal sonography should not be painful and is usually well tolerated by patients. Anxious patients may be given the option of inserting the probe into the vagina themselves. The probe is initially inserted with the marker-dot pointed toward the ceiling (Figure 55). The uterus is easily recognized upon insertion of the probe. This is the standard transvaginal sagittal view; it produces a longitudinal image of the uterus similar to the transabdominal sagittal view but rotated 90 degrees counterclockwise (Figure 56). The entire uterine midline stripe should be seen in this view. If the uterus is not seen immediately, then it may be anteverted and the probe should be aimed upward toward the anterior abdominal wall, keeping the marker-dot pointed toward the ceiling. Lateral movement of the probe can be used to scan from side to side through the entire pelvis. The uterus appears as a relatively hypoechoic structure with thick walls and a well-defined border. The endometrial midline stripe is thin during the proliferative phase and thick during the secretory phase of the menstrual cycle (Figure 57). The cervix can be seen by pulling the probe back a few centimeters and aiming the tip downward toward the patient’s back (Figure 58). In this view, inspect the posterior cul-de-sac for any evidence of free fluid.
 |  |
 |  |
After
the uterus is identified, the ovaries can be found by their position
relative to the uterus. They are usually found just lateral and
posterior to the body of the uterus, between the uterus and the lateral
pelvic wall. The sonographic appearance of the ovaries is distinct.
They are relatively hypoechoic structures containing multiple anechoic
follicles (Figure 59). To find the ovaries in sagittal oblique planes,
aim the probe laterally, with the marker-dot still toward the ceiling
(Figure 60). The internal iliac artery and external iliac vein can
often be identified and used as a guide because the normal position of
the ovary is adjacent to these structures (Figure 61). Sometimes the
ovaries cannot be identified with transvaginal sonography.3
 |  |
 |  |
The
standard transvaginal coronal view may be better for surveying the
entire pelvis. This view is obtained by turning the marker-dot toward
the patient’s right side (Figure 62). The coronal view gives a
transverse image of the uterus and allows the uterus and ovaries to be
seen in the same plane. The entire pelvis can be explored with oblique
coronal planes by aiming the probe up toward the anterior abdominal
wall and down toward the patient’s back, keeping the marker-dot
pointing toward the patient’s right side (Figure 63).
Transvaginal sonography is a dynamic imaging technique. To visualize structures, they need to be close to the tip of the probe. When structures are not readily visualized, operators should use their free hand to palpate the patient’s anterior abdominal wall, similar to performing a bimanual pelvic examination.4, 5, 6 Pressure on the anterior abdominal wall often brings an ovary or mass into the field of view. Also, the abdominal hand and the transvaginal probe can be used together to manipulate pelvic contents and observe how the organs move in relation to one another. An ovary may be easier to identify if it is seen as a discrete structure moving independently from adjacent loops of bowel. Also, structures that appear as complex masses may be comprised of multiple smaller structures that move independently of each other. Holding the transvaginal probe still and observing for bowel peristalsis is a good method for differentiating bowel from other pelvic structures. Finally, the tip of the transvaginal probe can be used to try to localize pelvic pain. This may help the physician to narrow the differential diagnosis when visualizing a mass or other abnormality.
Vascular Access
Ultrasound may be used to guide
any attempt at gaining vascular access, including central venous
access, peripheral venous access, and arterial access. When done
properly, ultrasound use decreases the incidence of complications,
including inadvertent arterial cannulation and pneumothorax. For any
vascular access, choose a linear or small parts probe with a
high-frequency range (Figure 64).
Static ultrasound images may be used to identify the structure to be cannulated and establish landmarks prior to the attempt. Dynamic imaging, however, allows real-time imaging of the needle entering the vein. To do this, the position of the vein is first obtained through the transverse view. Once the structure is centered in the transverse plane, the probe may be turned 90 degrees. A longitudinal view of the same vessel is now visible. In this way, the needle tip can be visualized entering the vein, and the wire is seen advancing through it. This technique does require some practice as it is important to keep the needle within the plane of the probe.
To use the transverse approach, orient the vein in the center of the probe just distal to the puncture site. Keep the probe marker on the right to avoid problems with orientation on the screen. Another tip is to touch the right side of the probe and see the image change on the right side of the screen. When gentle pressure is applied with the needle, its position should be apparent in the image as the structures just under the needle are displaced slightly posteriorly. Adjust the position of the needle as necessary to ensure entry just above the vein. This approach is useful to demonstrate the position of the needle in the coronal plane, but does not show the depth of the needle well.
The longitudinal approach, when used in conjunction with an echogenic-tipped needle, shows the depth of the tip in relation to the vein. The coronal plane orientation, however, is lost. This may be compensated for by keeping the entire needle within the plane of the probe. For best results, use a slightly more vertical approach–visualizing the tip of the needle from the moment it enters the skin to the moment it enters the vessel. Take care not to lose visualization of the tip. If the tip is not visible, gently sweep the needle from left to right until it is seen passing under the probe. Adjusting only the needle position, not the probe position, is ideal if the vessel is well seen under the probe.
Internal Jugular Access
Place
the probe in a transverse position over the carotid pulse on either
side of the lower neck, applying little pressure (Figure 65). Then
adjust the probe position until visualizing two roughly circular
hypoechoic structures. These should represent the internal jugular vein
and the carotid artery. The internal jugular vein is usually more
superficial and more lateral than the carotid, but its position may
change based on individual anatomy and head position. Application of
gentle pressure causes the vein to collapse while the artery should
remain patent. Color Doppler may also be used to visualize pulsations
in the artery, which will be absent in the vein. Then introduce the
needle directly into the vein under direct visualization (Figure 66).
The probe may also be turned in a longitudinal plane over the vein
(Figure 67) for an attempt at cannulation (Figure 68).
 |  |
 |  |
Femoral Vein or Artery Access
Place the probe in a
transverse position just distal to the inguinal ligament midway between
the pubic bone and the iliac crest. Move the probe medially until two
roughly circular hypoechoic structures are visible. These represent the
femoral vein and artery. With gentle pressure, the femoral vein
collapses while the artery remains patent. The desired structure is
centered and cannulation may be performed either in longitudinal or
transverse approach.
Peripheral Venous Access
For
this approach, place a tourniquet high on the arm. Employing a
transverse position of the probe, the depth of the image is set low as
only a vein less than 1 cm from the surface is usable with a peripheral
cannula (Figure 69). Use as little pressure as possible since a
collapsed vein will not be visible on the screen.
Veins collapse with gentle pressure, but arteries should not. The vein may then be cannulated, ideally under direct visualization.
References
- Townsend CM, Beauchamp RD, Evers BM, Mattox KL. Sabiston Textbook of Surgery, 18th ed. Philadelphia, PA: Saunders Elsevier; 2008.
- Halperin JL, Olin JW. Diseases of the aorta. In: Fuster V, Alexander RW, O’Rourke RA, Roberts R, King SB, Prystowsky EN, eds. Hurst’s the Heart, Vol 2, 11th ed. McGraw Hill Medical Publishing Division; 2004:2305
- Jones R, Blaivas M. The Handbook of Ultrasound in Trauma and Critical Illness. Columbus, OH: Ohio Chapter of ACEP; 2003.
- Ma OJ, Mateer JR, Blaivas M. Emergency Ultrasound, 2nd ed. New York, NY: McGraw Hill; 2008: 109-148.
- Zimmer EZ, Bronshtein M. Transvaginal scanning in pregnancy. In: Bronshtein M, Zimmer EZ, eds. Transvaginal Sonography of the Normal and Abnormal Fetus. New York, NY: Parthenon Publishing; 2001:48-50.
- DiSantis DJ, Scatarige JC, Kemp G, Given FT, Hsiu JG, Cramer MS. A prospective evaluation of transvaginal sonography for detection of ovarian disease. Am J Roentgenol. 1993;161:91-94.
- Lyons E, Levi C, Dashefsky S. The first trimester. In: Rumack C, Wilson S, Carboneau J, eds. Diagnostic Ultrasound. Vol. 2. St. Louis, MO: Mosby-Year Book, Inc.; 1998: 975-1011.
- Weston M. The first trimester. In: Dewbury K, Meire H, Cosgrove D, eds. Clinical Ultrasound: A Comprehensive Text. Vol. 3. London, UK: Churchhill Livingstone; 2001:151-187.
- Rottem S, Thaler I, Goldstein SR, Timor-Tritsch IE, Brandes JM. Transvaginal sonographic technique: targeted organ scanning without resorting to "planes." J Clin Ultrasound. 1990;18:243-247.
Acknowledgements
All
images contained in this portal are used with permission of the
Department of Emergency Medicine, Hennepin County Medical Center.
Thanks to Ben Dolan for his artistic contributions to this portal.