Markovchick Vincent J., Pons Peter T., Bakes Katherine M.(ed.) Emergency medicine secrets. 5th ed

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Jason S. Haukoos, MD, MSc

SHOCK

CHAPTER 4

1. Deﬁne shock.

A clinical syndrome characterized by widespread inadequate oxygenation and supply of

nutrients to tissues and organs resulting in cellular dysfunction.

2. How common is shock?

Although the prevalence is not precisely known, it is thought that shock constitutes

approximately 1% of all ED visits.

3. What is the overall mortality rate of patients who develop shock?

The mortality rate exceeds 20% for patients across all categories of shock.

4. List the ﬁve categories of shock and provide examples of each.

Hypovolemic: Examples: Trauma; gastrointestinal bleeding; ruptured ectopic

pregnancy; ruptured abdominal aortic aneurysm; and diabetic ketoacidosis.

Cardiogenic: Examples: acute myocardial infarction; cardiomyopathy; and valvular

dysfunction.

Distributive: Examples: sepsis; anaphylaxis; and spinal cord injury.

Obstructive: Examples: pulmonary embolism; cardiac tamponade; and tension

pneumothorax.

Toxic/Metabolic: Examples: carbon monoxide; cyanide; b-blocker; calcium channel

blocker; adrenal insufﬁciency; and thyroid storm.

5. How do you identify a patient in shock?

The successful treatment of an acutely ill patient with a high risk of death is predicated

on early recognition and treatment. A patient in shock will generally appear ill. Shock is a

clinical syndrome that reﬂects hypoperfusion. A brief focused history and targeted

physical examination will help determine if shock is present and its underlying etiology.

Examples of system-based symptoms and signs include:

Central nervous system: altered mental status.

Cardiovascular: decreased cardiac output; tachycardia; hypotension; and weak rapid

pulses.

Pulmonary: tachypnea; and hyperpnea.

Renal: decreased urine output.

Skin: delayed capillary reﬁll; cool and mottled in the setting of hypovolemic or

cardiogenic shock, and warm and moist in the setting of distributive shock.

6. How should urine output be used during resuscitation of a patient in

shock?

Patients in shock should have a Foley catheter placed to accurately measure urine

output. Urine output is an excellent indicator of organ perfusion, assuming the patient

had normal renal function at baseline. A normal urine output is .1.0 mL/kg/hour, a

reduced urine output ranges from 0.5 to 1.0 mL/kg/hour, and a severely reduced urine

output is ,0.5 mL/kg/hour. During resuscitation, targeted therapy should additionally

focus on improving or normalizing urine output.

Chapter 4 SHOCK 29

7. Describe compensated and decompensated shock.

Shock initiates a sequence of stress responses intended to preserve perfusion to vital organs.

Compensated shock occurs soon after the onset of shock and is marked by the maintenance

of tissue perfusion pressures. Such patients typically have evidence of a stress response

(e.g., tachycardia and tachypnea) but also have a normal or high blood pressure and normal

or mildly elevated serum lactate concentrations. If left untreated, compensated shock will

progress to decompensated shock, which is characterized by profound global tissue

hypoperfusion, elevated serum lactate concentration, and hypotension.

8. What is the initial management of a patient who presents in shock?

Management of patients in shock begins with the ABCs (i.e., airway, breathing, and

circulation). Due to poor delivery and uptake of oxygen, all patients should be placed on either

15 L of oxygen by nonrebreather mask or intubated. Simultaneously, all patients should have

large-bore intravenous access and be placed on a cardiac monitor.

9. Deﬁne oxygen delivery.

5 CaO

3 CO

, oxygen delivery

CaO

, arterial oxygen concentration

CO, cardiac output

CaO

5 (1.34 3 Hgb 3 SaO

) 1 (0.003 3 PaO

)

Hgb, hemoglobin

SaO

, arterial oxygen saturation

PaO

, arterial oxygen partial pressure

Oxygen delivery is the product of the cardiac output and arterial oxygen concentration.

Arterial oxygen concentration is deﬁned by the hemoglobin level, the arterial oxygen saturation,

and the arterial oxygen partial pressure. Maximizing cardiac output, hemoglobin, arterial oxygen

saturation, and the arterial partial pressure of oxygen will maximize oxygen delivery.

10. How useful are vital signs in assessing and treating someone in shock?

Vital signs are vital. Heart rate, respiratory rate, blood pressure, and pulse oximetry should

be monitored closely in patients in shock. Physiologic compensation and decompensation

(see Question 7) are commonly reﬂected in a patient’s vital signs. Additionally, normalization

of abnormal vital signs is one indicator of a patient’s response to resuscitation.

11. If a patient has normal vital signs, should I be reassured?

No. A patient’s heart rate and blood pressure may be normal in the setting of severe illness. In

the setting of shock, heart rate and blood pressure correlate poorly with cardiac output and

often underestimate the severity of systemic hypoperfusion.

12. Are orthostatic vital signs a sensitive indicator of hypovolemia? What

determines a positive orthostatic test?

To know what is abnormal, you ﬁrst must know what is normal. Studies on healthy euvolemic

people showed an average increase in pulse of 13 to 18 beats per minute with a large

standard deviation. A pulse increase of 20 beats per minute as a determinant for hypovolemia

is nonspeciﬁc because many normal individuals fall within this range. However, an increase of

30 beats per minute in heart rate is more speciﬁc. A 20% volume loss is required to produce

this change in heart rate, making this an insensitive test at best. The development of

symptoms (e.g., lightheadedness on standing) does not occur in healthy euvolemic individuals

upon standing and should be considered abnormal. Patients in shock should not be allowed to

stand to assess changes in vital signs.

Chapter 4 SHOCK30

13. Are there other signs that are helpful in assessing an acutely ill patient?

Yes. Besides vital signs, components of the physical examination (e.g., level of consciousness,

capillary reﬁll, and urinary output), you should pay close attention to the patient’s serum

lactate, central venous pressure (CVP), and central venous (ScvO

) or mixed venous (SvO

)

oxygen saturation.

14. How should I use and interpret a serum lactate?

Serum lactate is a commonly used marker to assess the extent of systemic hypoperfusion and

the degree to which a patient may be responding to resuscitation. In fact, it is an early marker of

systemic hypoperfusion and is often elevated prior to overt changes in a patient’s vital signs.

Therefore, liberal use of this marker may help identify patients earlier in their disease processes.

A serum lactate concentration .4 mEq/L is associated with the highest mortality rates.

15. What is the Lactate Clearance Index, and how can it be used during

resuscitation of a patient in shock?

The Lactate Clearance Index refers to measuring serum lactate concentrations at two or more

times during the course of the resuscitation. If after 1 hour of the beginning of resuscitation

efforts, the serum lactate concentration has not decreased by 50%, additional steps should be

undertaken to improve systemic perfusion.

16. What is a normal CVP and how is it measured?

A normal CVP ranges from 5 to 10 cm H

O. Central venous pressure is measured by attaching

an electronic pressure transducer or a water manometer to the end of an intravenous line

placed into the central venous system. The zero reference point for measuring a CVP is at the

point that bisects the fourth intercostals space and the midaxillary line in a supine patient,

corresponding to the position of the right atrium.

17. How is CVP used during resuscitation of a patient in shock?

The guiding principal for using the CVP is to normalize or supranormalize its value. The target

CVP should range from 10 to 15 cm H

O to maximize cardiac preload. In many shock states,

the heart becomes stiff and its function depressed. A supranormal CVP thus allows for

improved cardiac ﬁlling.

18. What is venous oxygen saturation, and what is the difference between a

ScvO

and SvO

Venous oxygen saturation provides a measure of tissue oxygenation (i.e., the balance between

oxygen supply [DO

] and demand [VO

]). SvO

is measured using a pulmonary artery catheter

and includes deoxygenated blood returning to the heart from the body, as well as

deoxygenated blood from the heart via the coronary sinus. It normally ranges between 65%

and 75%. ScvO

, on the other hand, is measured using a central venous catheter and

consistently overestimates (albeit to a small degree) venous oxygen saturation because it does

not include sampling of blood mixed with blood returning from the heart.

19. How do I use a ScvO

or a SvO

during resuscitation?

An ScvO

,65% suggests decreased oxygen supply or increased demand. In response,

attempt to improve oxygen delivery by increasing arterial oxygen saturation (SaO

) and/or

arterial oxygen partial pressure (PaO

) via oxygen supplementation; hemoglobin concentration

via transfusion; and/or cardiac output via inotropic support.

20. What is early goal-directed therapy?

Goal-directed therapy refers to the practice of resuscitating patients to deﬁned physiological

endpoints (e.g., mean arterial pressure, CVP, urine output, serum lactate concentration,

cardiac output, hemoglobin level, and SvO

), indicating that systemic tissue perfusion and

vital organ function have been restored. This has only been rigorously studied in patients with

sepsis; however, it has recently been evaluated in postcardiac arrest. It is likely that early

Chapter 4 SHOCK 31

goal-directed therapies will be evaluated in other forms of shock in the future, thus guiding

emergency physicians’ abilities to improve resuscitation endpoints and survival.

21. List the primary resuscitation goals in patients suffering from shock.

Maximize oxygenation.

Establish adequate ventilation.

Improve hemodynamic dysfunction.

Treat the underlying etiology.

22. What is the Trendelenburg position? What purpose(s) does it serve?

Trendelenburg refers to the patient placed in a supine, approximately 45-degree, head-down

position. The purposes of this position have been reported to include improving blood

pressure, redistributing circulating blood volume, placing central lines, and improving the

sensitivity of abdominal ultrasound for intra-abdominal ﬂuid. Although commonly used for the

purpose of improving hemodynamic parameters, several studies have not demonstrated its

utility in signiﬁcantly improving blood pressure or redistribution of blood volume.

23. Deﬁne systemic inﬂammatory response syndrome (SIRS).

SIRS is deﬁned by two or more of the following:

Temperature .38°C or 36°C.

Heart rate .90 beats per minute.

Respiratory rate .20 breaths per minute or partial pressure of carbon dioxide (PaCO

)

,32 mm Hg.

Serum white blood cell count .12,000 mm

or ,4,000 mm

or 10% band forms.

It is important to note that this deﬁnition, although standardized, is not speciﬁc for

deﬁning serious illness. Although most commonly related to sepsis, SIRS may result from a

variety of noninfectious insults, including trauma, burns, pancreatitis, and overdose.

24. Deﬁne sepsis, severe sepsis, and septic shock, and discuss their speciﬁc

therapies.

See Chapter 47.

25. How do I treat cardiogenic shock?

The treatment of cardiogenic shock should focus on improving myocardial contractility and

overall pump function. Provide oxygen and ventilatory support, including the judicious use of

noninvasive positive-pressure ventilation when pulmonary edema is present. Initiate inotropic

support using dobutamine or dopamine, and identify the etiology and administer speciﬁc

treatment (e.g., thrombolysis or percutaneous coronary intervention in the setting of acute

coronary syndrome). Consider intra-aortic balloon counterpulsation or cardiopulmonary

bypass for patients with refractory shock.

26. Explain the mechanism of dobutamine.

Dobutamine is a synthetic catecholamine with primarily b

-receptor (cardiac stimulation) and

mild b

-receptor (vasodilation) agonism.

27. Explain the mechanism of dopamine.

Dopamine is an endogenous catecholamine that when administered intravenously produces a

dose-dependent activation of adrenergic and dopaminergic receptors. When given in low doses

(e.g., 5 mg/kg/min), dopamine preferentially activates dopaminergic receptors, producing

vasodilatation in renal, mesenteric, and cerebral circulations. When given in intermediate doses

(e.g., 5 to 10 mg/kg/min), dopamine stimulates b-receptors, thus increasing cardiac output.

When given in high doses (e.g., .10 mg/kg/min), dopamine activates a-receptors, producing a

dose-dependent increase in systemic vascular resistance. It is important to note that dopamine

has modest inotropic characteristics when compared to dobutamine and that tachyphylaxis

may result from its use if used for a prolonged period of time.

Chapter 4 SHOCK32

28. How do I treat shock due to anaphylaxis?

See Chapter 18.

29. Explain the mechanism of epinephrine.

Similar to dopamine, epinephrine is a primary b-receptor agonist at low doses and an

a-receptor agonist at high doses. However, epinephrine is signiﬁcantly more potent than

dopamine.

30. How do I treat shock due to pulmonary embolism (PE)?

Massive PE causes shock by reducing the cross-sectional area of the pulmonary outﬂow tract,

thus increasing right-sided heart pressures, reducing blood ﬂow to the left side of the heart,

all of which results in a hemodynamic compromised state. Treatment centers on provision of

oxygenation and ventilation, hemodynamic support using crystalloids and vasopressors, as

necessary, and use of thrombolytics or surgical embolectomy in the setting of refractory

shock.

31. How do I treat shock due to cardiac tamponade?

As always, ensure adequate oxygenation and ventilation. Similar to other forms of obstructive

shock (e.g., PE), administration of intravenous ﬂuids may help overcome increased cardiac

ﬁlling pressures. However, the principal therapies for cardiac tamponade are

pericardiocentesis or pericardiotomy.

32. What is neurogenic shock and how is it treated?

Neurogenic shock is a form of distributive shock resulting from spinal cord injury in which

central or peripheral sympathetic tone is lost. Such patients are commonly hypotensive with

either a normal or low heart rate. Administer intravenous ﬂuids to normalize intravascular

volume. If hypotension persists, several vasopressor options exist, although intravenous

phenylephrine (0.15 to 0.75 mg/kg/min) is considered the classic ﬁrst-line agent.

33. Explain the mechanism of phenylephrine.

Phenylephrine is a pure and potent a-agonist. Administration of this agent can induce a reﬂex

bradycardia, resulting in decreased cardiac output.

KEY POINTS: SHOCK

1. Shock is deﬁned as a clinical syndrome characterized by widespread inadequate

oxygenation and supply of nutrients to tissues and organs, resulting in cellular dysfunction.

2. The ﬁve categories of shock are hypovolemic, cardiogenic, distributive, obstructive, and

toxic/metabolic.

3. Serum lactate is a commonly used marker to assess the extent of systemic hypoperfusion

and the response to resuscitation.

4. The primary resuscitation goals in patients suffering from shock are to maximize oxygen-

ation, establish adequate ventilation, improve hemodynamic distribution, and treat the under-

lying cause.

Chapter 4 SHOCK 33

BIBLIOGRAPHY

1. Abramson D, Scalea TM, Hitchcock R, et al: Lactate clearance and survival following injury. J Trauma 35:

584–588, 1993.

2. Bell RM, Krantz BE: Initial assessment. In Mattox KL, Feliciano DV, Moore EE, editors: Trauma, ed 4,,

New York, 2000, McGraw-Hill, pp 153–170.

3. Bone R: American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference:

deﬁnitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Crit Care Med

20:864–874, 1992.

4. Gaieski DF, Band RA, Abella BS, et al: Early goal-directed hemodynamic optimization combined with therapeutic

hypothermia in comatose survivors of out-of-hospital cardiac arrest. Resuscitation 80:418–424, 2009.

5. Kline JA: Shock. In Marx J, editor: Rosen’s emergency medicine: concepts and clinical practice, ed 5,

St. Louis, 2002, Mosby, pp 33–47.

6. Marino PL: The ICU book, ed 2, Baltimore, 1998, Williams & Wilkins.

7. Nguyen HB, Rivers EP, Knoblich BP, et al: Early lactate clearance is associated with improved outcome

in severe sepsis and septic shock. Crit Care Med 32:1637–1642, 2004.

8. Rivers EP, Amponsah D: Shock. In Wolfson AB, editor: Harwood-Nuss’ clinical practice of emergency

medicine, ed 4, Philadelphia, 2005, Lippincott Williams & Wilkins, pp 36–43.

9. Rivers EP, Nguyen B, Havstad S, et al: Early goal-directed therapy in the treatment of severe sepsis and septic

shock. N Engl J Med 8:1368–1377, 2001.

10. Shapiro NI, Howell MD, Talmor D, et al: Serum lactate as a predictor of mortality in emergency department

patients with infection. Ann Emerg Med 45:524–528, 2005.

CHAPTER 5

EMERGENCY ULTRASOUND

John L. Kendall, MD, FACEP, and Catherine Erickson, MD

1. What is ED ultrasound all about?

An ultrasound probe in the hands of the clinician has historically been considered the

stethoscope of the 21st century. Extending beyond this deﬁnition, the technology of

ultrasound is increasingly considered to be an integral part of the evaluation and

management of ED patients.

2. Why should ultrasound be performed in the ED?

Focused ultrasound examinations performed by ED physicians allow for more timely,

less invasive, and safer evaluations of patients. Ectopic pregnancy and biliary colic may

be evaluated rapidly, intra-abdominal traumatic hemorrhage may be diagnosed without

the invasiveness of diagnostic peritoneal lavage or the delay of a computed tomography

(CT) scan, and patients with major trauma or suspected abdominal aortic aneurysm

(AAA) may be evaluated quickly in the safety of the ED.

3. How does emergency ultrasound differ from ultrasound performed by the

radiology department?

Emergency ultrasound is meant to be a focused, goal-directed examination. Speciﬁc

ﬁndings, such as the presence of intraperitoneal ﬂuid in blunt abdominal trauma;

intrauterine pregnancy (IUP) in suspected ectopic pregnancy; gallstones, wall thickness,

or sonographic Murphy’s sign in right upper quadrant pain; aortic dilation in suspected

AAA; and pericardial ﬂuid in patients with possible pericardial tamponade, are used to

guide patient care. In contrast, a radiologist-performed ultrasound is more

comprehensive in that all structures viewed are evaluated.

4. How about some basic ultrasonography physics?

Ultrasound images are generated as sound waves at various frequencies (MHz) that

reﬂect off tissue interfaces. The higher the ultrasound frequency, the greater the

resolution but at the expense of reduced tissue penetration. Dense tissues, such as

bone or gallstones, appear bright because most of the ultrasound energy is absorbed

or reﬂected. Solid organs, such as the liver or spleen, show a gray scale of tissue

architecture. All of the ultrasound energy passes through ﬂuid or blood, leaving a black

(anechoic) area on the screen. Ultrasound energy does not propagate well through air.

Thus, lung, hollow viscous structures, and air trapped within soft tissues are difﬁcult to

visualize. In general, abdominal and cardiac examinations utilize a 3.5- to 5-MHz probe,

transvaginal ultrasound examinations a 7.5- to 10-MHz probe, and vascular studies a

10- to 12-MHz specialized probe.

5. Describe the basics of the trauma ultrasound examination.

The trauma ultrasound examination (also known as the focused assessment with

sonography for trauma [FAST]) is done rapidly at the patient’s bedside during the

secondary survey. The primary goal is to detect free intraperitoneal ﬂuid, which appears

as anechoic areas within the peritoneal cavity. Sites in the abdomen that are evaluated

are the potential spaces that occur at dependent sites within the peritoneal cavity. These

include the hepatorenal recess or Morison’s pouch (Fig. 5-1), splenorenal recess,

retrovesicular recess (pouch of Douglas in females), and both pericolic gutters. Oblique

Chapter 5 EMERGENCY ULTRASOUND 35

views of the right and left chest are

obtained to search for hemothorax, and

a subxiphoid or left parasternal cardiac

image is obtained to locate pericardial

effusion (Fig. 5-2).

6. Where is the best place to look

for intraperitoneal ﬂuid?

The sonographic examination should

include all sites previously mentioned.

The sensitivity increases from

approximately 60% if one site is

viewed to almost 90% if all are used.

7. How does ultrasound compare

with traditional means of

evaluating the traumatic

abdomen?

Physical examination is only 50% to

60% sensitive for detecting abdominal

injuries after blunt trauma. Diagnostic

peritoneal lavage is 95% sensitive but

is not speciﬁc, resulting in unnecessary

laparotomies. CT is sensitive for

detecting abdominal injuries (.95%)

but is costly, is time consuming, and

requires the patient to leave the ED.

Prospective studies of ultrasound

showed an 83% to 90% sensitivity for

the detection of hemoperitoneum, with

sensitivity approaching 100% in

patients who were hypotensive from an abdominal source. The accuracy of ultrasound to

detect the underlying parenchymal lesion varies widely.

8. How should I use ultrasound in my evaluation of blunt trauma patients?

Consider patient scenarios based on vital signs and ultrasound ﬁndings:

a. Stable vital signs, negative ultrasound

b. Stable vital signs, positive ultrasound

c. Unstable vital signs, negative ultrasound

d. Unstable vital signs, positive ultrasound

KEY POINTS: PRIMARY CHARACTERISTICS

OF THE EMERGENCY ULTRASOUND EXAMINATION

1. Performed for a deﬁned indication

2. Focused, not complete

3. Easily learned and quickly performed

4. Directed toward one or two easily recognizable ﬁndings

5. Directly impacts clinical decision making

6. Performed at the bedside

Figure 5-2. Subxiphoid cardiac view shows a

pericardial effusion.

Figure 5-1. View of Morison’s pouch showing

intraperitoneal ﬂuid.

Chapter 5 EMERGENCY ULTRASOUND36

Patients with stable vital signs and a negative ultrasound who have no other signiﬁcant

injuries, have normal mental status, and are not intoxicated can be managed with observation,

serial physical examinations, and serial ultrasound studies. Patients with stable vital signs and

a positive ultrasound warrant an abdominal CT scan. If the vital signs are unstable and

ultrasound is negative or indeterminate, a bedside diagnostic peritoneal lavage can be done

and other etiologies of hypotension considered. If the vital signs are unstable and the

ultrasound is positive for free ﬂuid, the patient should go directly to laparotomy.

9. Can I tell how much intraperitoneal ﬂuid is present based on the ultrasound

image?

No, conﬂicting data exist. No study has yet shown an accurate means of quantifying the

amount of intraperitoneal ﬂuid that is present based on its sonographic appearance.

10. What are some of the pitfalls I may encounter during a trauma ultrasound

examination of the abdomen?

Although relatively rare, one of the

more concerning aspects of emergency

ultrasound is the false-negative study.

In terms of abdominal trauma, clotted

blood is the ﬁnding that mimics a

negative study the closest. An example

of clotted blood found in Morison’s

pouch is shown in Fig. 5-3. It initially

was interpreted to be liver parenchyma

because of a similar echogenic pattern.

False-positive ﬁndings that simulate

hemoperitoneum can occur in the

setting of ascites, urine from a ruptured

bladder, bowel contents from bowel

perforation, perinephric fat, and

ﬂuid-ﬁlled stomach or bowel.

11. What is the sonographic appearance of the gallbladder and related

structures?

The gallbladder is cystic, so the

sonographic appearance is a pearlike

structure that is anechoic. Surrounding

this anechoic area is a ring of

midechogenicity that corresponds to the

gallbladder wall. Normally, it is less than

4 mm wide, but can be thicker

immediately after eating or if in

edematous states, such as liver failure,

ascites, congestive heart failure, renal

disease, or AIDS. Stones are typically

circular in nature, can be of any size, and

are bright, or hyperechoic, on their

proximal side. Ultrasound does not

penetrate stones well, so distal to the

stone there is a shadow (Fig. 5-4). This

also is called the headlight sign,

signifying the presence of a calciﬁed

gallstone. Sludge is a collection of the precipitants of bile that layers within the gallbladder and

appears sonographically as mildly echogenic material without any shadowing.

Figure 5-3. Clotted blood in Morison’s pouch.

Figure 5-4. Long-axis view of the gallbladder

shows a gallstone. The gallstone is represented

by an echogenic proximal surface and distal

attenuation shadow.

Chapter 5 EMERGENCY ULTRASOUND 37

12. What ﬁndings are suggestive of acute cholecystitis?

The primary ﬁndings of the emergency gallbladder ultrasound are the presence of gallstones

and a sonographic Murphy’s sign (deﬁned as maximal tenderness over an ultrasound-detected

gallbladder). The presence of these primary ﬁndings has a 92% positive predictive value and a

95% negative predictive value for the presence of cholecystitis. Other ﬁndings, such as wall

thickening (.4 mm), ductal dilation (.6 mm), pericholecystic ﬂuid, sludge, and an

emphysematous gallbladder, are considered to be secondary ﬁndings and are less reliably

seen by emergency sonographers. Ultrasound is insensitive at detecting choledocholithiasis.

13. What are the indications for pelvic ultrasonography in the ED?

Ultrasonography is the imaging study of choice for evaluating abdominal pain or bleeding in

pregnant patients in the ﬁrst or second trimester. The goal of ED ultrasound is to establish the

presence of an IUP, so as to effectively rule out an ectopic pregnancy. Ectopic pregnancy is

the second leading cause overall of maternal mortality and the number one cause of maternal

mortality during the ﬁrst trimester.

14. How early can an IUP be detected using ultrasound? What value of b-human

chorionic gonadotropin (HCG) does this correspond to?

An IUP may be detectable as early as 4.5 weeks by transvaginal ultrasound at a b-HCG level

of 1,000 to 2,000 mIU/mL (6 weeks or greater with a b-HCG of 5,000 mIU/mL using

transabdominal ultrasound). The discriminatory zone, or level of b-HCG at which one would

expect to see evidence of an IUP, depends on the institution where the patient is being seen.

A gestational sac is seen at approximately 4-5 weeks gestational age and cardiac activity can

be measured as early as 6 weeks gestational age.

15. How sensitive is ultrasound for the evaluation of ectopic pregnancy?

Several studies have shown that 75% to 80% of patients have a diagnostic ultrasound

(i.e., either an IUP or a demonstrable ectopic pregnancy). The problem is that in the remaining

20% of patients with nondiagnostic ultrasounds, nearly one fourth have ectopic pregnancies.

This increase in ectopic pregnancy among patients with nondiagnostic ultrasound suggests

that this group should have thorough evaluation, including an obstetric-gynecologic

consultation in the ED.

16. Describe the pitfalls in pelvic ultrasonography.

For emergency physicians, the goal of pelvic ultrasonography is to determine whether an IUP

is present. It is not clear how well emergency physicians evaluate the adnexa, pelvic free ﬂuid,

or ovaries. Cornual pregnancies may be mistaken for an IUP, with an attendant risk of rupture

and hemorrhage. The question of heterotopic pregnancies (i.e., simultaneous IUP and ectopic

pregnancy) must be considered. In populations without risk factors for ectopic pregnancy, the

risk of a heterotopic gestation is approximately 1 in 30,000 pregnancies. The incidence

increases markedly, however, in patients with preexisting pelvic inﬂammatory disease or

scarring and is greatest for patients receiving medical fertility assistance, in whom the

incidence is estimated to be 1 in 100 to 1 in 400 pregnancies. A pseudosac can be seen in

20% of ectopic pregnancies. It is formed in response to the b-HCG produced by the abnormal

pregnancy. It consists of a single-ringed structure in the endometrial cavity, and it can be

mistaken for a true gestational sac, which consists of two concentric rings.

17. What other abdominal structures can be evaluated by emergency ultrasound?

Evaluation of the abdominal aorta can be useful in elderly patients who present with a pulsatile

abdominal mass, nontraumatic abdominal pain or ﬂank pain, hypotension of unknown cause,

or unexplained pulseless electrical activity. AAA is manifested by aortic diameter greater than

3 cm with most symptomatic aneurysms being greater than 5 cm (Fig. 5-5). Studies by

emergency physicians showed sensitivity of 100% and a speciﬁcity of 98% for the detection

of AAA. Studies showed a 90% correlation of ultrasound-determined aortic diameter to

pathologic specimens.