Volume I:
First Thirty Minutes
- Section 1
  Acute Care Algorithm/ Treatment Plans/ Acronyms
- Section 2
  Universal Approach
  - CALS Universal Approach To Emergency Advanced Life Support
- Section 3
  Steps 1-6
- Section 4
  Preliminary Impression/Focused Clinical Pathways
Volume II:
Resuscitation Procedures
Volume III:
Definitive Care

Ultrasound 1: Emergency Ultrasound Applications Portal

Ultrasound in Trauma
Bedside ultrasound has become the initial imaging test of choice for trauma care and is part of the Advanced Trauma Life Support (ATLS) protocol. Ultrasound is highly effective because it can be performed simultaneously with other resuscitative procedures, providing vital information without the time delay caused by radiographs or computed tomography (CT).

Due to distracting injuries, altered mental status, and other factors, physical exam may be unreliable in the trauma setting. Bedside ultrasound permits clinicians to identify free fluid (usually blood) that may occur without obvious physical signs in the pericardial, pleural, or peritoneal spaces, allowing early recognition of bleeding into all regions of the torso, except the retroperitoneum. Bedside ultrasound has also been proven to be useful in the setting of both blunt and penetrating torso trauma.^{1, 2}

Using bedside ultrasound, clinicians may quickly determine the etiology of hypotension in unstable trauma patients as well as recognize occult internal bleeding prior to decompensation in stable trauma patients.

The FAST Exam
Focused Assessment with Sonography for Trauma (FAST) has become synonymous with beside ultrasound in trauma cases.^{3, 4} The FAST exam is usually performed immediately after the primary survey. FAST helps to immediately narrow the differential diagnosis during trauma resuscitation. Some trauma centers have recently begun performing an extended FAST (EFAST) exam, using bedside ultrasound to look for a pneumothorax and hemothorax in trauma patients.^5-7 Bedside ultrasound has been shown to be equivalent to, or better than, chest radiography for identifying a hemothorax or pneumothorax in multiple-trauma patients.^{5, 6, 8, 9}

Immediate life-threatening injuries cause bleeding. Although ultrasound is not 100% sensitive for identifying all bleeding, it is highly effective for recognizing intraperitoneal bleeding that causes shock in hypotensive patients who require emergent laparotomy.^{10, 11} Bedside ultrasound is also highly effective for diagnosing cardiac injuries from penetrating trauma.^{12, 13}

Common Injuries and Indications for Ultrasound in Trauma
Penetrating Cardiac Trauma
Bedside ultrasound significantly decreases mortality in patients with penetrating cardiac injuries.13 Most patients with stab wounds to the heart do not suffer significant blood loss because the pericardium seals the wound, creating a pericardial effusion. Cardiac tamponade will eventually develop, but in most cases there is an asymptomatic period of several minutes or hours. When symptoms of cardiac tamponade develop, clinical decompensation occurs rapidly, resulting in cardiac arrest. Even after tamponade develops, the classic signs of Beck’s triad are not commonly present and are difficult to determine by physical exam alone. Therefore, try to identify a developing pericardial effusion as early as possible, ideally before cardiac tamponade or cardiac arrest occurs. To accomplish this, use bedside ultrasound liberally and screen all patients with penetrating chest injury for pericardial effusion. An effusion is usually easily seen as a rim of dark fluid bounded by the pericardium. Clot may also be present and is slightly more echogenic than blood. If pericardial effusion is present, assume cardiac injury until proven otherwise and dispatch the patient directly to the operating room for a pericardial window or sternotomy.

Blunt Cardiac Trauma
Significant blunt cardiac injury is relatively uncommon. Most patients who suffer severe cardiac injury, such as rupture of the free wall, probably die at the scene.

Although blunt cardiac injury is rare, perform prompt cardiac ultrasound in all patients with significant blunt chest trauma, especially those who are hypotensive.¹⁴ Cardiac rupture causes a pericardial effusion, which is easily recognizable during the FAST exam. Severe global ventricular dysfunction may also be noted, but this is usually the result of severe acidosis from hypovolemic shock.

Blunt Abdominal Trauma
Intraperitoneal bleeding after blunt abdominal trauma is common and is usually the result of a spleen or liver injury and is difficult to diagnose on physical exam. The FAST exam is effective for early recognition of intraperitoneal blood since FAST is rapid, safe, sensitive, and can be repeated if the patient’s status changes.

The volume of intraperitoneal blood that can be detected using the FAST exam depends on the skill of the operator and views obtained. To optimize sensitivity to detect the smallest amount of free fluid possible, obtaining good images of multiple intraperitoneal sites is important.¹⁵ A high-quality FAST exam can probably reliably detect about 200 mL of free intraperitoneal fluid. If quality images of the pelvis are obtained (which requires more technical skill), even smaller volumes may be detected. Placing a patient in the Trendelenburg position improves the sensitivity for detecting free fluid in the Morison's pouch view.¹⁶Trendelenburg positioning is reasonable when the pelvic view is indeterminate or difficult to visualize. Overall, the FAST exam is about 90% sensitive for detecting any amount of intraperitoneal free fluid.¹ Sensitivity is greatly increased by performing serial FAST exams in patients with high suspicion for intra-abdominal injury. In unstable patients, a positive FAST exam mandates exploratory laparotomy. In stable patients, CT scanning may be performed to focus further management.

Penetrating Abdominal Trauma
As in blunt trauma, the FAST exam can be used to detect intraperitoneal bleeding in patients with penetrating trauma.^1-2,10 In addition, the FAST exam can be used to help prioritize initial management in patients with multiple penetrating injuries or unknown missile trajectory.¹⁷ Within minutes after patient arrival, the FAST exam allows clinicians to determine whether to concentrate initial efforts on a cardiac, chest, or intraperitoneal injury or whether to address multiple sites of injury simultaneously.

Not all intraperitoneal injuries can be detected using ultrasound. Bowel injuries are common in penetrating trauma, and the FAST exam does not detect most bowel injuries.

Chest Trauma With Hemothorax
Evaluation for chest hemothorax is now a routine part of the FAST exam.¹⁸ Hemothorax—common in both blunt and penetrating trauma—can usually be managed with simple chest tube placement. A hemothorax may be difficult to recognize by physical exam and is often missed on chest radiograph. About 200 mL of pleural fluid is required before it can be detected on a plain chest radiograph.¹⁹ Even a large hemothorax can be missed on supine chest radiograph. Ultrasound is much more sensitive for detecting pleural fluid, and can identify as little as 20 mL in the pleural space.²⁰ Blood appears as a dark triangle above the diaphragm.^a

Chest radiographs are still necessary to evaluate the mediastinum, lung parenchyma, and several other anatomic features in trauma patients. Ultrasound can be used during the initial minutes of the trauma evaluation to determine whether urgent chest tube placement is needed. A chest radiograph can then be obtained for the usual reasons and to check chest tube placement. This approach saves valuable time when managing an unstable, multiple-trauma patient.^{9, 18}

Chest Trauma With Pneumothorax
Pneumothorax is common after blunt and penetrating trauma, and more than half of pneumothoraces are missed on supine chest radiograph.²¹ Bedside ultrasound is more sensitive (and quicker⁹) than chest radiography for detecting a pneumothorax.^{6, 21-23} Using ultrasound to look for occult pneumothoraces is most important in situations where missing a small pneumothorax could result in significant deterioration, positive pressure ventilation (PPV), or helicopter transport. Consider using ultrasound to prompt early chest tube placement in unstable trauma patients with multiple severe injuries.

Other Uses of the FAST Exam
The FAST exam aids in diagnosis of a variety of conditions outside trauma. Intra-abdominal fluid from many etiologies, including ruptured ectopic pregnancy, intra-abdominal rupture of abdominal aortic aneurysm (AAA), ascites, and ruptured hemorrhagic ovarian cyst may be easily identified. Similarly, pleural effusions (due to pneumonia, malignancy, and pulmonary edema) as well as spontaneous and iatrogenic pneumothoraces may be seen. A cardiac window may be utilized to visualize a pericardial effusion caused by malignancy, uremia, pericarditis, or many other etiologies. When used as such, ultrasound can greatly enhance the physical exam.

Abdominal Aortic Aneurysm
AAA is relatively common in patients > 50-years-old.^24-26 Misdiagnosis is also common because patients usually have no previous diagnosis, may present with no symptoms (or nonspecific complaints), and have normal vital signs.^27-29 Patients do not usually know that they have an aneurysm. Most patients appear initially well until rupture occurs.^{28,
30, 31-33} Rapid diagnosis and early surgical intervention prior to and after rupture clearly decreases mortality.^34-39

Bedside ultrasound has been shown to be nearly 100% accurate for detecting or ruling out an AAA,^{27, 29, 40-43} decreasing time to diagnosis and operative intervention while greatly improving survival.³⁹ The main indication for bedside aortic ultrasound is to rapidly identify patients with a ruptured AAA. Administer immediate bedside ultrasound exam to all patients with signs or symptoms potentially attributable to a ruptured AAA.

Reasonable indications for bedside aortic ultrasound include all patients > 50-years-old with the following signs or symptoms:

Classic triad of ruptured AAA
- abdominal, back, or flank pain
- palpable abdominal mass
- hypotension
Pain consistent with ruptured AAA
Unexplained hypotension, dizziness, or syncope
Cardiac arrest

Diagnosis prior to rupture is advantageous since early recognition and repair carries much lower mortality.^b Delayed or missed diagnosis occurs because the symptoms may mimic other common conditions such as renal colic, diverticulitis, gastrointestinal hemorrhage, sepsis, or acute coronary syndrome.^{28, 32, 33, 44}

Classic Triad of Ruptured AAA
Unfortunately, this triad (as described above) is usually not present,⁴³ (although may be found in < 25% of cases).^{28, 31, 33, 44, 45} Pain is the most consistent symptom (present in > 80% of patients)^{28, 31, 33} as well as the most common reason patients seek medical care. Patients often present with referred pain to the scrotum, buttocks, thighs, shoulders, chest, or other locations. ²⁵ When patients present with non-specific pain and stable vital signs, it is common to miss or delay diagnosis. Do not consider any patient stable with known or suspected AAA rupture, regardless of initial vital signs.³²

Abdominal palpation for diagnosis of AAA is unreliable and is not present in many cases, even in thin patients. Nonetheless, perform palpation as part of your exam, and if positive, should again prompt ultrasonographic confirmation. Although not universally present, hypotension is present in ≥ 50% of patients with ruptured AAA.^{28, 30, 31-33, 53} Most aneurysms rupture into the retroperitoneum, resulting in a transient tamponade effect. At time of presentation, 30% to 50% of patients have a normal blood pressure. ^{28, 30, 31-33, 53}

Relative hypotension, orthostatic hypotension, dizziness, or syncope may be precursors to overt hypotension and are indications for aortic sonography. Relative hypotension occurs in patients with baseline hypertension who have a decrease in blood pressure but still have values within normal range. These patients may present with altered mental status, vague weakness, dizziness, or syncope. Maintain a high index of suspicion for ruptured AAA in such patients.

Altered mental status secondary to hypotension can make it difficult to obtain a history of abdominal, back, or flank pain. Therefore, patients may present with unexplained hypotension and no other clue of a ruptured AAA.

Cardiac arrest is fairly common.³⁸ Cardiac arrest with pulseless electrical activity (PEA) often represents a state of severe hypotension and may be reversible if the cause is rapidly identified and aggressively treated.⁵⁴ Some physicians argue that patients who have a cardiac arrest from a ruptured AAA have a minuscule chance of survival and that surgical repair is a waste of resources,⁵¹ but this view is not supported by current data.^c

Focused Bedside Echocardiography
The primary indications for application of limited bedside echocardiography in the emergency department (ED) or critical care setting are cardiac arrest, suspected pericardial effusion or massive pulmonary embolism (PE), assessment of left ventricular (LV) function, unexplained hypotension, estimation of central venous pressure (CVP), and evaluation of external cardiac pacing.⁵⁵ Bedside echocardiography also a component of the FAST exam in the setting of known trauma.

Cardiac Arrest
During cardiac arrest and resuscitation, bedside echocardiography allows clinicians to directly visualize the heart to determine the presence and amount of mechanical cardiac function. Bedside echocardiography can quickly determine if a patient with PEA has true electromechanical dissociation (EMD) with cardiac standstill or pseudo-EMD, mechanical cardiac contractions too weak to create a palpable blood pressure.⁵⁶ Ultrasound is also useful in differentiating between asystole and fine ventricular fibrillation.⁵⁷ The most common causes of PEA are hypovolemia, hypoxia, acidosis, hypo/hyperkalemia, hypoglycemia, hypothermia, drug overdose, cardiac tamponade, tension pneumothorax, massive myocardial infarction, massive PE, and trauma.⁵⁸ Many of these conditions can be rapidly detected with bedside cardiac ultrasound.

Hypovolemia
Patients in cardiac arrest from severe hypovolemia have a small, empty- appearing heart (Figure 1).⁵⁹ Both the right and left ventricles (RV and LV) are poorly filled and the RV is almost completely collapsed. The LV is hyperdynamic and vigorously beating. The inferior vena cava (IVC) is collapsed in both expiration and inspiration (Figure 2).

Severe LV dysfunction from massive myocardial infarction, acidosis, drug overdose, hypothermia, or electrolyte abnormality is characterized by global ventricular hypokinesis, absent or incomplete valve closure, or accumulation of an intracardiac hyperechoic clot. The IVC is usually dilated and poorly compliant during inspiration, indicative of elevated right-sided filling pressures (Figure 3).

Pericardial Effusion
A pericardial effusion usually shows as anechoic or black, fluid collection encircling the heart (Figure 4). The subcostal view is best for detection of pericardial effusion. Evidence of cardiac tamponade is diastolic collapse of any heart chamber in the presence of a pericardial effusion, most frequently the right atrium and/or RV.⁵⁷ Other signs of tamponade are paradoxical movement of the interventricular septum and engorgement and stiffening of the IVC.⁶⁰ Paradoxical interventricular movement may be difficult to visualize but evaluation of the IVC is straightforward. Again, the enlarged and noncompliant IVC is due to elevated right heart filling pressures and the backup of blood into the IVC as it returns to the heart.

Pulmonary Embolism
Limited echocardiography is useful for making a diagnosis of massive PE.^61-63 In patients presenting with a massive PE, the RV is obviously enlarged with a thin wall and is often bulging into the left heart (Figure 5). This is due to outflow obstruction and increased pressure in the RV. There may be evidence of right heart failure with RV wall hypokinesis and paradoxical interventricular septal movement. There is an engorged IVC with minimal respiratory compliance changes. Many chronic clinical conditions cause RV strain, including chronic obstructive pulmonary disease (COPD), pulmonary hypertension, and pulmonary stenosis. Use bedside ultrasound in correlation with the clinical scenario to help direct the diagnostic and therapeutic course of a patient.

Estimate of Left Ventricular Function
Bedside echocardiography can be used for direct visualization of LV function and estimation of the ejection fraction (EF). Assess LV function in broad terms: normal EF >55%, depressed EF 30% to 50%, or severely depressed EF <30%. Global function is normal if all walls of the myometrium uniformly contract and move significantly from diastole to systole. A hypokinetic LV will have minimal movement between diastole to systole and may have gross wall motion abnormalities. LV dysfunction is often coupled with a dilated, poorly pliable IVC.

Shock
Unexplained hypotension, or shock, is a common presentation in the ED.⁵⁵ Bedside echocardiography in undifferentiated shock allows real-time assessment of global cardiac function, chamber size, and gross estimation of CVP. This helps to assign hypotensive patients to a specific hemodynamic category: cardiogenic shock (from severe LV dysfunction, cardiac tamponade, or PE), hypovolemic shock, or septic shock.⁶⁰

As discussed, hypotension from cardiogenic shock is evident by global wall motion abnormalities and hypokinesis. Hypotension from a massive PE shows a large RV with thin walls and a concomitant hyperdynamic LV. Hypovolemic shock causes low filling pressures and subsequently a contracted empty-appearing RV. The LV is also poorly filled and usually has normal or hyperdynamic function. The IVC may be difficult to visualize or be very small and easily collapsible with significant hypovolemia. This is opposite to the appearance of the IVC in cardiogenic shock, cardiac tamponade, or a large PE. In patients with sepsis, the global cardiac function is normal or hyperdynamic, while the IVC is small and easily collapsible during inspiration.

CVP Estimate
An estimate of CVP may be obtained through direct visualization of the IVC as blood returns to the right atrium. Assessment of the size and respiratory variations of the proximal IVC cannot provide the absolute CVP but can determine if the CVP is very low or very high. In general a large IVC correlates with a higher CVP (Figure 2), and a small IVC correlates with a lower CVP (Figure 3).⁵⁵ There is usually significant respiratory variation in the size of the IVC. During inspiration, negative intrathoracic pressure draws blood out of the IVC into the right atrium causing the IVC to collapse. Complete collapse of the IVC during inspiration is consistent with a low CVP, while the lack of significant size variation during inspiration is consistent with a high CVP. This amounts to a non-invasive CVP measurement and may be helpful in patients with hypotension and uncertain volume status.⁶⁴ Keep in mind that PPV causes dilation of the IVC, making these measurements less useful after a patient is intubated.

Transcutaneous Pacing
The final primary indication for bedside echocardiography is the assessment of ventricular capture in transcutaneous pacing (TCP).^65-67 A real-time cardiac ultrasound during TCP can determine the effectiveness of subsequent cardiac contractions. If there are ineffective cardiac contractions with electric capture, quickly make management changes to correct this effective state of PEA.

Emergency cardiac echocardiography is a rapid, non-invasive, and real-time method to provide critical information about cardiac structure and function. It should be a goal-directed examination to answer defined clinical questions. When learning bedside echocardiography, focus on the standard views. These allow quick detection of pericardial effusions and cardiac tamponade as well as assessment of global cardiac function. Since ultrasound has no contraindications and does not expose patients to ionizing radiation,⁵⁵it can be repeated many times during a patient’s stay in the ED, critical resuscitation, and diagnostic and therapeutic course. No other diagnostic imaging modality can provide this level of continual data about cardiac function.

First Trimester Pregnancy
Introduction
Ultrasound is the primary imaging modality used in pregnancy.^{68, 69} In first trimester patients who present with vaginal bleeding or abdominal pain, ultrasound can be used to distinguish ectopic pregnancy from threatened abortion or embryonic demise. The primary goal of emergency sonography of the pelvis during the first trimester is to identify an intrauterine pregnancy, which essentially excludes the diagnosis of ectopic pregnancy.⁷⁰ Sonography can immediately establish one of these diagnoses in most patients with first trimester complaints.⁷¹

Secondary objectives are to detect extrauterine signs of an ectopic pregnancy, estimate the viability of an intrauterine pregnancy, and characterize other causes of pelvic pain and vaginal bleeding. In addition, sonographic detection of free fluid outside of the pelvis can help to expedite the care of a patient with a ruptured ectopic pregnancy.⁷²Emergency bedside sonography is not intended to define the entire spectrum of pelvic pathology in early pregnancy. A formal pelvic ultrasound, by medical imaging or obstetric specialists, is indicated after an initial emergency bedside screening examination.

Indications
Abdominal or pelvic pain and vaginal bleeding are common complaints during early pregnancy. Challenges to emergency or acute care physicians include making the diagnosis of pregnancy, using serum beta-hCG or a urine pregnancy test, and then using available diagnostic tools to determine the etiology of the patient’s complaint.

Any patient at risk for complications of early pregnancy is a candidate for pelvic sonography. Symptoms and physical examination findings include pelvic or abdominal pain or tenderness, vaginal bleeding, dizziness, syncope, a pelvic mass, or uterine size that does not correlate with gestational age. Risk factors for ectopic pregnancy include pelvic inflammatory disease (PID), tubal ligation, tubal surgery, increased maternal age, intrauterine contraceptive devices, prior ectopic pregnancy, and history of infertility.⁷³ Most patients with an ectopic pregnancy present with abdominal or pelvic pain, vaginal bleeding, or dizziness, but some patients are relatively asymptomatic. No specific sign or symptom is absolute. Maintain a high index of suspicion so that subtle presentations are not overlooked.

Administer an immediate abdominal and pelvic ultrasound examination to any woman of childbearing age who presents with shock of unknown etiology, even before a pregnancy test has been completed.⁷²

Emergency pelvic sonography is useful for the diagnosis of multiple pregnancy, pregnancy loss, and ovarian torsion. These common diagnoses can be challenging and are covered briefly. Pelvic sonography is used to evaluate pelvic mass and gestational trophoblastic disease in the first trimester of pregnancy, but these diagnoses are beyond the realm of this course and are not covered.

Normal Pregnancy
A normal intrauterine pregnancy is the most common sonographic finding during the first trimester. Even novice sonographers can use pelvic ultrasound effectively because identifying an intrauterine pregnancy is simple and this finding virtually eliminates the possibility of an ectopic pregnancy.⁷⁴ About 70% of patients who present with abdominal pain or vaginal bleeding in the first trimester have an intrauterine pregnancy visualized with bedside ultrasound and do not require further testing.⁷⁵ Take care when using sonography between 3 and 5 weeks gestational age because it is easy to confuse sonographic signs of an early intrauterine pregnancy with those of an ectopic pregnancy.

Both transvaginal and transabdominal sonography can be used to detect an early intrauterine pregnancy. Transvaginal ultrasound can identify an intrauterine pregnancy at about 5 weeks gestational age (3 weeks post-conception), about 7 to 10 days earlier than transabdominal ultrasound.

Transvaginal sonography is now the standard modality for evaluating early pregnancy. Using transvaginal sonography, a gestational sac can be clearly identified at about 5 weeks. In most patients, this corresponds with beta-hCG levels of 1000 to 2000 mIU/mL and in all patients with levels above 2000 mIU/mL.⁷⁶ A gestational sac is characterized by a sonolucent center (chorionic sac) surrounded by a thick symmetric echogenic ring, known as the chorionic rim. This finding is seen in most intrauterine pregnancies but can also be seen surrounding a pseudogestational sac associated with an ectopic pregnancy.⁷⁷ Identification of a simple gestational sac should not be used as definitive evidence of an intrauterine pregnancy.

Many authors consider a clear double decidual sign as the first definitive evidence of an intrauterine pregnancy.^77-79The double decidual sign is two concentric echogenic rings surrounding a gestational sac (Figure 6). The inner ring is the same structure as the chorionic ring and is called the decidua capsularis. The outer ring is called the decidua vera, derived from the stimulated endometrium of the uterus, while the thin hypoechoic layer between them is the endometrial canal.^79-81 A gestational sac with a vague or absent double decidual sign is not diagnostic of an intrauterine pregnancy and may be a pseudogestational sac. If two clear rings are seen, an intrauterine pregnancy is likely. Unfortunately, the double decidual sign is present in only about half of all intrauterine pregnancies and is not 100% accurate.⁸²

The yolk sac is the first structure that can be seen inside the gestational sac. Some authors consider the yolk sac the first definitive evidence of intrauterine pregnancy.^{78, 83} It is probably prudent for inexperienced sonographers to visualize the yolk sac before making a diagnosis of an intrauterine pregnancy, avoiding misinterpretation of more subtle findings like the double decidual sign. The yolk sac is a symmetric circular echogenic structure at the edge of the gestational sac (Figure 7). The yolk sac can first be seen by transvaginal sonography at about 5 to 6 weeks and then shrinks and disappears by about 12 weeks.⁸⁴

The embryo appears as a thickening or small mass that is seen at the margin of the yolk sac between 5 and 6 weeks. The normal embryo grows rapidly, about 1 mm per day. The embryo can first be seen when it is only 2 to 3 mm and cardiac activity may not be detectable initially. By 6 weeks, the embryo is a distinct structure separate from the yolk sac.

Cardiac activity should be detected within the embryo at about 6 weeks. Any embryo measuring greater than 5 mm should have cardiac activity when transvaginal sonography is used (Figure 8). At 7 weeks, the embryo is about 12 mm and the head of the embryo is clearly distinguished. At 8 weeks, the head of the embryo is about the same size as the yolk sac and limb buds begin to appear. At 8 weeks and beyond, a thin echogenic line, the amnionic sac, may be seen surrounding the embryo.

At 10 weeks, organogenesis is complete and the embryo is now referred to as a fetus (Figure 9). Between 10 weeks and the end of the first trimester, the contours of the fetus become much more obvious, and discrete structures such as limbs, organ detail, and the face can be visualized.

When an embryo is visible, at about 6 weeks, measurement of the crown-rump length (CRL) of the embryo should be used to date the pregnancy (Figure 10).⁸³ When measuring CRL, it is important to measure the maximal embryo length, excluding the yolk sac. Errors can occur when the calipers are not carefully placed at the margins of the embryo. Also, the embryo can flex and extend slightly, changing the measurement. Nevertheless, gestational age determination by CRL is accurate to within 5 to 7 days.⁸⁵

Measurement of the biparietal diameter (BPD) of the fetal skull is used for pregnancy dating at the end of the first trimester and during the second trimester. The BPD is a transverse measurement of the diameter of the skull at the level of the thalamus. The calipers should be positioned from the leading edge of the skull (outer table) on the near side to the leading edge of the skull (inner table) on the far side (Figure 11). Errors can be made by measuring the wrong part of the skull or if the image plane is not a true transaxial section through the fetal head. Pregnancy dating by BPD is also very accurate, especially prior to 20 weeks gestation.⁷⁷

Multiple Pregnancy
Patients occasionally present with a fundal height greater than their predicted gestational age based on last menstrual period. These patients should be evaluated with pelvic ultrasound to assess accuracy of dates using CRL and BPD. Often these measurements reveal inaccuracy in the patient’s estimated date of conception. Occasionally, however, a multiple pregnancy is visualized explaining the discrepancy between the measured fundal height and estimated date of conception. Multiple pregnancies are relatively easy to visualize at approximately 6 weeks gestation and later, seen as two or more discrete embryos (Figure 12). It is important to scan through the entire uterus in both the sagittal and transverse planes in order to detect multiple pregnancies.

Ectopic Pregnancy
In the presence of a positive urine pregnancy test, absence of an intrauterine pregnancy is an ectopic pregnancy until proven otherwise. A live extrauterine embryo with cardiac activity can be seen with transvaginal sonography in about 15% to 20% of ectopic pregnancies.^86,
87An extrauterine gestational sac containing an embryo or yolk sac is also diagnostic and is seen in a significant percentage of ectopic pregnancies (Figure 13).⁸⁷

Several nonspecific sonographic findings are not diagnostic but are highly suggestive of an ectopic pregnancy in pregnant patients with an empty uterus. Some findings are subtle and may be easily missed, especially if transvaginal sonography is not available or an inexperienced sonographer performs the scan. Therefore, emergency physicians should obtain a formal ultrasound if no intrauterine pregnancy or ectopic pregnancy is identified with emergency bedside sonography.

Free fluid in the posterior pelvic cul-de-sac or in other intraperitoneal sites is highly suggestive of ectopic pregnancy (Figure 14).^88-90 Transvaginal sonography is sensitive for detecting free fluid in the posterior cul-de-sac.⁸⁰ Only about one-third of ectopic pregnancies have no free fluid in the cul-de-sac.⁸⁵ Also, free fluid is the only abnormal sonographic finding in about 15% of ectopic pregnancies.⁹⁰ The greater the volume of free intraperitoneal fluid, the greater the likelihood of ectopic pregnancy.⁷⁷ In fact, patients with a moderate to large amount of free pelvic fluid have ~86% chance of ectopic pregnancy and those with hepatorenal free fluid have ~100% chance of ectopic pregnancy.⁸⁹ Although a large amount of fluid predicts ectopic pregnancy, it is not a reliable indicator of tubal rupture. Only ~60% of those with a large amount of free fluid have a ruptured tube.^{88, 91} Free fluid may be due to leaking of blood from the end of the fallopian tube, which can occur slowly.

Echogenic fluid more likely represents blood, and this increases the chances of ectopic pregnancy. If bleeding is brisk, clots may be seen in the pelvic cul-de-sac instead of fluid. Although a small amount of hypoechoic free pelvic fluid may be normal, consider this finding suspicious in a pregnant patient with an empty uterus.^{33, 40, 43, 92} The definition of “small amount” is fluid that is confined to the cul-de-sac and covers less than one-third of the inferior posterior uterus. As stated, anything more than a small amount is almost always associated with an ectopic pregnancy.^{40, 43, 53}

Perform abdominal sonography of the hepatorenal space (Morison’s pouch) on every patient with a possible ectopic pregnancy.^7,8 Free fluid in the hepatorenal space (Figure 15), or elsewhere outside the pelvis, is evidence of a large amount of intraperitoneal fluid.²⁷ In a pregnant woman with an empty uterus, this must be considered bleeding secondary to ectopic pregnancy. Finding free fluid in the hepatorenal space with emergency bedside sonography reduces the time to diagnosis and treatment of ectopic pregnancy.¹¹ A finding of hepatorenal free fluid “should give the surgeon a greater sense of urgency.”⁸

A tubal ring is nearly diagnostic of ectopic pregnancy.^{19, 20, 23, 28} A tubal ring is a concentric hypoechoic structure found in the adnexa (Figure 16). It is created by the trophoblast of the ectopic pregnancy surrounding the chorionic sac and is the equivalent to a gestational sac.⁸ A tubal ring has a different sonographic appearance than a corpus luteum cyst or other ovarian cysts because it has a relatively thick and brightly echogenic, round, symmetric wall. Ovarian cysts have walls of varying thickness and are surrounded by normal ovarian follicles. With transvaginal sonography, it may be possible to identify a tubal ring in more than 60% of ectopic pregnancies.^{19, 20} When a tubal ring is seen, the likelihood of ectopic pregnancy is > 95%.²⁰

The most common sonographic finding in ectopic pregnancy is a complex adnexal mass (Figure 17).²⁹ A complex adnexal mass may represent a tubal hematoma, ectopic trophoblastic tissue, or distorted contents of an ectopic gestational sac.^{7, 19, 20, 23, 34} A complex mass contains a mixture of cystic and solid components. This is a sensitive sonographic sign of ectopic pregnancy. When an experienced sonographer performs a transvaginal scan, it may be seen in up to 85% of cases.²⁰ However, a complex mass may be subtle and easily missed.⁷

Several sonographic signs may help to differentiate a complex mass from the surrounding pelvic structures. Identifying the ovaries and then searching between the ovaries and the uterus is the best technique for locating an adnexal mass. To differentiate a mass from other pelvic structures, examiners should press down on the patient’s lower abdomen with their free hand during transvaginal scanning, in a manner similar to performing a bimanual pelvic examination. This causes pelvic structures to move in relation to one another, and examiners can recognize a mass as a separate structure, moving independently from the ovary and bowel. Also, if the transvaginal probe is held very still, peristalsis of the bowel can be seen, differentiating the mass from other pelvic structures.

Fetal Demise
Several sonographic signs can reliably predict embryonic demise. The earliest sign is a gestational sac without a yolk sac or embryo (Figure 18). For the purposes of emergency bedside transvaginal sonography, an empty gestational sac > 20 mm is a good predictor of embryonic demise; this is referred to as a blighted ovum.

Another good indicator of embryonic demise is lack of embryonic cardiac activity. With transvaginal sonography, cardiac activity should be seen in all embryos > 5 mm long by CRL.^{77, 80, 93, 94} With transabdominal sonography, cardiac activity should be seen in all embryos > 10 mm long.⁷⁷When searching for embryonic cardiac activity, be sure that the embryo is clearly seen. This is easier at 7 to 8 weeks gestation, when the embryonic head and torso can be identified.

Embryonic bradycardia predicts a poor prognosis.^{95, 96} The normal heart rate for an embryo longer than 5 mm by CRL (6.3 weeks gestational age) is > 120 beats per minute (bpm).⁹⁵ The lower the HR below 120 bpm, the lower the predicted survival rate of the embryo.

In all cases, interpret findings of embryonic demise conservatively and give the pregnancy the benefit of the doubt. Ordering a formal ultrasound and obtaining an obstetrics consult is prudent when diagnosis is unclear.

The uterus should be empty after a completed spontaneous abortion. A small amount of blood or clot may be present. Patients with intrauterine echogenic material or a thickened midline stripe (> 10 mm wide) after spontaneous abortion probably have retained products of conception.^97-99 When curettage is performed, chorionic villi are identified in about 70% of cases.⁹⁸ Many patients with retained products do well with expectant management but may require curettage. Monitor closely for bleeding and infection.⁹²

Adnexal Torsion
Most cases of adnexal torsion occur in the presence of an enlarged ovary or an ovarian mass. The normal ovary measures between 2 cm and 3 cm in diameter (Figure 19). An ovary larger than 5 cm in diameter is abnormal and should raise suspicion for torsion. Finding an ovary normal in size and appearance makes the diagnosis of adnexal torsion unlikely. However, if the diagnosis is suspected, a formal ultrasound is required.

Second and Third Trimester Pregnancy
In patients with bleeding in the second or third trimesters of pregnancy, use bedside ultrasound primarily to evaluate viability of the fetus and look for abnormalities of the placenta. Interpret results of any bedside ultrasound given in the second or third trimesters of pregnancy with the assistance of an obstetrician.

Viability of the fetus is determined by cardiac activity. If the fetus has no heartbeat, fetal demise has occurred, and further intervention will likely not succeed. If cardiac activity is present but slow, presume the fetus to be in significant distress.

Viability of the fetus is also determined by gestational age. If a patient is uncertain of her last menstrual period or her estimated date of confinement and there is no access to medical records, ultrasound of the fetus provides an estimate of gestational age. The two preferred methods for this are BPD and femur length. Obtain a transverse view of the fetal head demonstrating the third ventricle and the thalami. Measurement should be of a diameter that crosses through all these structures. Measure from the outer aspect of the near skull to the inner wall of the far skull (Figure 20). A femur length should include only ossified portions of the femur (Figure 21).

Tables for the normal range of heart rate, BPD, and femur length for given gestational ages are widely available on the internet. Calculators are usually preloaded into commercially available ultrasound machines. Obtain this information and convey promptly to a consulting obstetrician to determine need for transfer, surgical intervention, or further monitoring.

The primary emergent differential in late pregnancy vaginal bleeding is placenta previa versus placental abruption. Placenta previa occurs when the placental edge is too close to the cervix. As the pregnancy progresses and the cervix changes shape, the placenta is pulled away and causes bleeding. Typically this bleeding is painless. If placenta previa is suspected, digital exam of the cervix is absolutely contraindicated. Placental abruption, in contrast, is hemorrhage that occurs between the placenta and the uterine wall. It is usually, but not always, painful. Abruption may also present with abdominal pain only, without external vaginal bleeding. (Vol III—OB7 Bleeding in the Second Half of Pregnancy)

The role of ultrasound in evaluating the placenta is primarily to rule out placenta previa. Using an abdominal probe in a longitudinal position over the lower portion of the abdomen, visualize the lowest portion of the placenta in relationship to the cervix. If the placenta overlies the cervix, this is indicative of placenta previa (Figures 22, 23, 24).

Placental abruption might be seen as a collection of fluid between the placenta and the uterine wall, but the echogenicity of the fluid can vary from hyperechoic to hypoechoic. Ultrasound, however, cannot rule out placental abruption because the abruption may have been decompressed externally and a hematoma may not be visible. If no placenta previa is seen, presume vaginal bleeding in late pregnancy to be abruption. Immediate involvement of an obstetrician in the decision-making process is warranted in suspected placenta previa or placental abruption.

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Acknowledgement

All images contained in this portal are used with permission of the Department of Emergency Medicine, Hennepin County Medical Center.

Ultrasound 1: Emergency Ultrasound Applications Portal

References

Edition 13-October 2011