Chapter 16: Surgeon Performed Ultrasound in Acute Care Surgery

Ultrasound is routinely incorporated into the work-up of patients with a variety of trauma, critical care, or emergency surgical disorders.^1,2,3,4,5,6 Despite advances in other superior imaging modalities such as multidetector-row computed tomography (MDCT), the ability to acquire real-time data with ultrasound allows the surgeon to make critical decisions expeditiously with minimal risk of complications. Surgeons are personally capable of obtaining good quality images and interpreting the examination independently.^7,8,9 Presently, medical students, surgical residents and fellows have become familiar with the management of trauma patients and those with emergency general surgery problems using ultrasound as they have multiple opportunities to learn the technique of bedside ultrasound examination.¹⁰ Similarly, the management of critically ill patients including resuscitation, hemodynamic monitoring, and procedural guidance has drastically changed in the past few decades as the ultrasound examination is more commonly performed.^{11,12,13,14,15} These critical care ultrasound studies can be completed at the bedside and avoid transporting patients from the intensive care unit (ICU). In addition to basic techniques to identify free fluid in the abdominal cavity, surgical intensivists have successfully applied the advanced echocardiographic examination to guide the resuscitation of critically ill patients.^16,17,18 This chapter reviews the indications, techniques, and currently available data for ultrasound examinations in trauma, emergency general surgery, and critical care patients.

Ultrasonography is operator-dependent. Therefore, an understanding of select principles of ultrasound physics is necessary so that images may be acquired rapidly and interpreted correctly. Knowledge of these basic principles enables the acute care surgeon to select the appropriate transducer, optimize resolution of the image, and recognize artifacts. Some basic terms and principles of physics relative to ultrasound imaging in the acute setting are defined in Tables 16-1, 16-2, 16-3.

In general, an ultrasound system includes the following components: (1) a transmitter that controls electrical signals sent to the transducer; (2) a receiver or image processor that admits the electrical signal; (3) a transducer containing piezoelectric crystals to interconvert electrical and acoustic energy; (4) a monitor to display the ultrasound image; and (5) an image recorder or printer.^19,20 The ultrasound images that are obtained depend on the orientation of the transducer or probe relative to the structure or organ being imaged, with each transducer having an indicator that directs its orientation to the screen. The indicators on most probes are oriented such that placing the indicator cephalad in a coronal or sagittal plane or to the left in the transverse plane will orient the image correctly. This left to right convention is typically reversed in cardiac imaging presets that are employed in focused echocardiography examinations. As the image may be purposefully reversed by a machine adjustment, the surgeon should confirm the orientation of the probe by adding ultrasound gel to the probe’s footprint and gently rubbing it to visualize where the motion is detected on the screen (Fig. 16-1). This should allow the surgeon to determine how the indicator will orient the image. The orientations or scanning planes are described in Table 16-4.²¹

Although diagnostic ultrasound uses transducer frequencies ranging from 1 to 30 MHz (megahertz = 1 million cycles/s), medical diagnostic imaging most often uses frequencies between 2.5 and 10 MHz (Table 16-5). Accordingly, transducers are chosen on the basis of the depth of the structure or organ to be imaged. High-frequency transducers (≥5 MHz) provide excellent resolution for imaging superficial structures such as a thyroid nodule or an abscess in the soft tissue of an extremity. Lower-frequency transducers emit waves that penetrate deeply into tissue and are preferred for visualizing organs such as the liver or spleen.^19,22,23

Since the 1980s, ultrasound has been used to detect free fluid such as blood in the pericardial and intraperitoneal spaces in acutely injured patients.^24,25 This simple, rapid, and accurate ultrasound technique was adopted in the United States in the 1990s and subsequently named the focused assessment with sonography for trauma (FAST).²⁶ The application of ultrasound has expanded to other areas of the body to identify injuries and help to direct the management in the prehospital setting and in the emergency room.

Technique of FAST—General Principles

The FAST examination is performed by a trauma team member (trauma surgeon, emergency medicine physician, trainee, or advanced practice provider) (Fig. 16-2). Although a designated examiner typically performs the FAST examination, the care provider who conducts the primary and secondary survey may also complete the FAST sequentially. The patient’s chest and abdomen are exposed during the primary survey. Trauma patients are normally placed in the supine position during the primary and secondary survey of the advanced trauma life support algorithm.²⁷ Therefore, dependent portions in the abdominal cavity should be scanned to identify abnormal hypoechoic areas (ie, free fluid). In many institutions, a small size portable ultrasound machine is attached to the bedside tower in the emergency room (Fig. 16-3). For the FAST examination, either a sector- or convex-shaped transducer (low-frequency: 2.5–5.0 MHz) is used to visualize the pericardial space and relatively deep regions in the abdominal cavity. A linear-shaped transducer (high-frequency: ≥7.5 MHz) is not suitable for this reason (Fig. 16-4). Before starting the examination, the image settings including depth or gain should be adjusted. Recording of real-time images is required for review to ensure quality of the FAST examination. The entire examination should not require more than 5 minutes, even in the hands of trainees. The goal of the FAST examination is to detect or exclude fluid in the pericardial space and abdominal cavity.

Pericardial Examination

The FAST examination typically starts with visualizing the heart so that the image settings, such as gain or depth, can be optimized (with a known fluid-filled structure). The intracardiac blood should be anechoic, and the posterior heart should be visualized on the screen. First, a transducer is placed in the subxiphoid region for a sagittal or transverse view of the heart. The transducer should be directed toward the head of the patient under the xiphoid process. In this position, the heart will be visualized beneath the left lobe of the liver. This sagittal view enables the examiner to view simultaneously the inferior vena cava and was prescribed in the original description of the FAST examination. A transverse view allows the provider to visualize more pericardial surface area, although more pressure is applied with consequent pain. A pericardial effusion is seen as an anechoic area around the heart (Fig. 16-5). Both the anterior and posterior wall of the heart should be visualized as a small effusion can otherwise be missed. For patients with severe injury to the chest and/or abdominal wall, subcutaneous emphysema, a narrow costal angle or a thick thoracoabdominal wall, appropriate views may not be obtainable through this window. Alternate views include the apical view or parasternal view in which the transducer is placed adjacent to the left nipple or along the sternum in the second intercostal space.

Abdominal Examination

There are three dependent spaces that are scanned in the abdominal portion of the FAST examination as follows: the hepatorenal recess (Morison’s pouch), the splenorenal recess and the pelvis around the bladder. To obtain a longitudinal view in the hepatorenal recess, the transducer is placed in the right upper quadrant (RUQ) of the abdomen. Although this view is often called the “RUQ view,” optimal views typically are obtained in the right mid-to-posterior axillary line at the level of the 9th to 12th ribs. The right lobe of the liver and the right kidney should be visualized in the same view (Fig. 16-6). Fanning the transducer to visualize the right kidney from one side to the other is the key to preventing a false-negative examination, and free fluid can be identified between the liver and kidney. For patients with a significant amount of intraperitoneal fluid, this fluid may also be visualized above the anterior surface of liver. The longitudinal view of the splenorenal recess is obtained next in the left upper quadrant (LUQ). The transducer should be oriented more superiorly and posteriorly than the RUQ to visualize (Fig. 16-7). Trauma patients often present with a full stomach that can be misread as free fluid. Thus, it is imperative to visualize the spleen and the left kidney in the same image (Fig. 16-8). Finally, sagittal and transverse views are obtained in the pelvis. The transducer is placed a few centimeters above the pubic symphysis. The FAST examination is ideally performed before an indwelling urinary catheter is placed. Fluid inside (urine) and outside (blood) of the bladder is visualized as an anechoic area separated by the bladder wall (Fig. 16-9).

Data in Blunt Trauma Using the FAST Examination

The utility of the FAST examination has been examined most extensively in patients with blunt torso injury.^{2,7,28,29,30,31,32,33,34,35} Since the 1990s, many prospective and retrospective studies have been conducted in various patient populations. A significant disparity in data regarding the FAST examination is due to different inclusion criteria and outcomes of interest (intraperitoneal fluid vs any intra-abdominal injury). Accuracy of the FAST examination can be affected by several factors including hemodynamic stability (a likely surrogate for amount of fluid) or associated injuries.^36,37 Currently, the most appropriate indication for the use of the FAST examination is for hypotensive patients with blunt torso injuries. A large prospective study conducted by Rozycki et al. demonstrated that surgeon-performed FAST was 100% sensitive and 100% specific for detecting hemoperitoneum in hypotensive patients with blunt abdominal trauma.³⁸ Patients with a positive FAST examination (showing intra-abdominal free fluid) should be taken to the operating room emergently for exploratory laparotomy. In contrast, a negative FAST examination should not be used to rule out a serious intra-abdominal injury in patients with unstable vital signs. The patient should not be transported to the CT scanner, unless a repeat FAST is negative 15 minutes later. Another option is to perform a bedside diagnostic peritoneal aspiration (DPA) as a more sensitive test to determine the presence of intraperitoneal bleeding than the FAST examination. Further, it is known that the FAST examination may not be sensitive for intraperitoneal fluid in patients with pelvic fractures. Friese et al. reported that the sensitivity of the FAST examination performed by surgical residents for high-risk patients with pelvic fracture (age >55, systolic blood pressure [SBP] <100 mm Hg or unstable pattern fracture) was only 26.1% to detect intraperitoneal fluid.³⁶ Even for patients with a SBP < 100 mm Hg, the FAST examination was not reliable to rule out a hemoperitoneum (sensitivity 36.4%). Although several studies have been reported showing the utility of the FAST examination in detection of intraparenchymal injuries involving solid organs, the FAST examination has a low sensitivity to detect intra-abdominal injuries that are not associated with intra-abdominal fluid.^8,39,40 In the series by Chiu et al., 29% of patients with blunt abdominal injury had no hemoperitoneum.⁸ In these patients, the FAST examination was interpreted as negative, although CT imaging identified grade 2–3 splenic and hepatic injuries.

Pericardial fluid secondary to a cardiac injury is rarely seen in patients with blunt trauma. Therefore, there are scarce data regarding the accuracy of the FAST examination to detect this fluid in such patients. A series early in the 1990s had no patients with pericardial fluid after blunt trauma.³⁸ Press et al. focused on the cardiac component of the FAST examination in blunt trauma using institutional databases.⁴¹ Out of 29,236 patients with blunt trauma evaluated over 7 years, only 14 patients were identified with a hemopericardium and 3 patients with cardiac rupture, respectively. Further, the incidence of hemopericardium confirmed in the emergency cardiac ultrasound was 0.13%.

Data in Penetrating Trauma Using the FAST Examination

Patients with penetrating injury to the anterior chest can potentially sustain life-threatening injuries. A cardiac injury with an associated hemopericardium should be identified rapidly and accurately regardless of a patient’s hemodynamic stability, as early detection of these injuries improves the prognosis. Thus, using ultrasound for patients with penetrating wounds in the so-called “cardiac box” is another appropriate indication for the FAST examination. A prospective multicenter study by Rozycki et al. examining patients with a precordial or transthoracic wound at five Level 1 trauma centers suggested that a hemopericardium could be identified in all patients without any false-negative examinations (sensitivity 100%).⁴² Therefore, patients with a positive pericardial view should have an emergent sternotomy or thoracotomy based on the very high specificity (96.9%). These data were consistent with results from other series of the precordial FAST examination. A pitfall in interpreting the pericardial FAST examination for patients with a suspected penetrating cardiac injury is that pericardial blood can decompress into the thoracic cavity if there is an associated laceration of the pericardial sac.⁴³ In these cases, a patient could present with a hemothorax without evidence of hemopericardium on the FAST examination.

The utility of the FAST examination is limited in patients with penetrating abdominal trauma as compared to blunt trauma. Hemodynamically unstable patients with a penetrating injury require operative intervention regardless of the result of the FAST examination. Similarly, patients with peritonitis should be explored no matter what the FAST examination shows. Therefore, ultrasound examination is not included in the algorithm suggested by the Western Trauma Association based on a multicenter study to guide the management of patients with anterior abdominal stab wounds.⁴⁴ This is supported by multiple studies showing a low sensitivity of the FAST examination for intra-abdominal injuries.^45,46 While Rozycki et al. showed comparable sensitivity and specificity for the FAST examination in patients with penetrating wounds (sensitivity: 83.8%, specificity: 97.4%), subsequent studies consistently failed to replicate this accuracy.⁷ In the aforementioned multicenter study, the FAST examination was performed in half of hemodynamically stable and asymptomatic patients with abdominal stab wounds.⁴⁴ Of these, only 21% of patients who required therapeutic laparotomy had a positive FAST examination. Similarly, Soffer et al. conducted a prospective cohort study to include patients with both stab and gunshot wounds.⁴⁷ A majority of the FAST examinations were performed by trauma surgeons or surgical trainees. Sensitivities of the FAST examination for therapeutic laparotomy in patients with stab and gunshot wound were 47% and 49%, respectively. Approximately 40% of injuries to a hollow viscus, the most common injury identified at exploratory laparotomy, were missed by the FAST examination. Furthermore, authors have indicated that initial FAST findings rarely alter the management (3/177 cases). To date, there are no studies to report the role of the FAST examination in hemodynamically unstable patients with penetrating injury. For unstable patients with multicavitary penetrating injury (eg, thoracoabdominal injury), the FAST examination can be a useful tool to guide the surgeon to decide which cavity needs to be explored first.

Technique of E-FAST (Extended FAST)

Thoracic injuries are fairly common in multisystem blunt or penetrating trauma to the torso.⁴⁸ The ATLS protocol emphasizes the importance of identifying life-threatening thoracic injuries including pneumothorax and hemothorax during the primary and secondary survey.²⁷ Frequently, these injuries are missed on a physical examination as patients do not present with classic signs. Although a chest x-ray (CXR) is considered the gold standard to screen for these serious thoracic injuries, equipment or personnel may not be readily available in certain circumstances. Further, because of the patient’s position (supine) and other factors such as a backboard, foreign bodies, and/or associated injuries, the quality of the CXR may not be adequate for use as a screening tool. The application of thoracic ultrasound in trauma patients was reported as a part of ultrasound examination in the 1990s.⁴⁹ Initially, the thoracic component was not incorporated into the FAST examination; however, recent enthusiasm exists for this application of ultrasound in trauma patients. Thus, an extended FAST (E-FAST) examination is often performed in the trauma bay to detect thoracic injuries.

The E-FAST is normally performed as a continuation of the FAST examination. It is not necessary to change the position of the patient (supine) or the type of transducer (low-frequency sector or convex type). The primary goal in the thoracic part of the E-FAST examination is to detect air (pneumothorax) and/or fluid (hemothorax) in the thoracic cavity. After the pericardial and abdominal examination, the transducer is placed longitudinally in the mid-axillary line, a few costal spaces more cephalad than the area for the RUQ FAST examination. This view should include the right lobe of the liver and diaphragm which has respiratory excursion. A hemothorax is seen above the diaphragm as an anechoic area (Fig. 16-10). In patients with a moderate to large hemothorax, passively collapsed lung parenchyma is detected as a hypoechoic structure. This maneuver is repeated on the left side to scan the entire thoracic cavity. The transducer should be placed more posteriorly and cephalad to visualize the left hemidiaphragm. The reminder of the E-FAST examination can be performed with either the same low-frequency transducer or a high-frequency (7.5–10 MHz) linear transducer. When a low-frequency transducer is used, the depth of image needs to be adjusted to focus on more superficial structures of the anterior thoracic wall. Patients should be maintained in the supine position as the goal of this maneuver is to identify a pneumothorax located anteriorly. The transducer is placed in the midclavicular line longitudinally. In order to obtain an optimal view, the transducer should be placed in the intercostal spaces (superior, mid, and lower levels). In normal individuals, a “lung sliding” sign can be observed. This is the finding whereby the parietal and visceral pleurae (both hyperechoic linear structures) are moving in relation to each other. Similarly, “comet tails” are visualized in normal individuals due to artifacts generated by reverberation of the ultrasound waves. This sign is named for vertical, hyperechoic lines arising from the pleural line (Fig. 16-11). These two signs (sliding and comet tails) are not observed in patients with a pneumothorax, who have air between the parietal and visceral pleurae. If an ultrasound machine with an M-mode (motion mode) function is used, the cursor is placed perpendicular to the pleural line. While linear and granular patterns are seen above and below the pleural line, respectively, in normal lung (“seashore sign”), a linear pattern both above and below the pleural line, the so-called “barcode sign,” is appreciated in those with a pneumothorax (Fig. 16-12). An even more specific ultrasonographic sign for a pneumothorax is called the “lung point.” The transition zone between normal lung and the pneumothorax is apparent by the seashore (normal) and barcode signs (abnormal) aligning on M mode or the sliding lung (normal) adjacent to the nonsliding lung (abnormal) in B mode imaging (Fig. 16-13).

Data in Trauma Patients using the E-FAST

Application of thoracic ultrasound in the trauma setting has been described since the 1990s.^49,50 In an early series reported by Ma et al., thoracic ultrasound performed by emergency medicine physicians on 240 patients with both blunt and penetrating trauma had a sensitivity of 96.2%, a specificity of 100%, a positive predictive value of 100%, a negative predictive value of 99.5%, and an accuracy of 99.6% to detect a hemothorax confirmed by either tube thoracostomy or computed tomography.⁵⁰ Surgeon-performed ultrasound to detect a hemothorax had similar results (sensitivity: 97.5%, specificity: 99.7%) to that of the CXR, but with a significantly shorter examination time (1.30 ± 0.08 vs 14.18 ± 0.91 minutes, p < 0.0001).⁵¹ Other early studies that examined the sensitivity and specificity of the ultrasound for a hemothorax also showed promising results comparable to the CXR. The utility of ultrasound to detect a pneumothorax was demonstrated in the 1990s for patients in the ICU.⁵² Bedside ultrasound can be helpful to expedite care in patients with unstable vital signs. In trauma patients, Knudson et al. conducted a prospective study to evaluate surgeon-performed ultrasound to detect a pneumothorax.⁵³ As previously noted, the diagnosis of a pneumothorax was made based on the absence of the lung-sliding sign and/or the comet-tail artifact. Of note, a low-frequency (2.5–4 MHz) transducer was used in this study. In comparison with the CXR, ultrasound had a sensitivity of 92.3%, a specificity of 99.6%, a positive predictive value of 92.3%, a negative predictive value of 99.7%, and an accuracy of 99.3%.

Ultrasound-guided Resuscitation in the Emergency Department

The resuscitation of severely injured patients should be initiated immediately in the trauma bay. While damage-control resuscitation has been proposed for a decade, invasive hemodynamic monitoring devices to guide the resuscitation are not always available until the patient is transferred to the ICU. Two components of information that should be obtained using ultrasound are the intravascular volume status (preload) and contractility of the heart. The assessment of intravascular volume status can be estimated by measuring the diameter and collapsibility of the inferior vena cava (IVC) using ultrasound (Fig. 16-14).⁵⁴ In one study, non-cardiologists successfully visualized the IVC to measure the diameter in 89% of trauma and surgical patients.⁵⁵ The assessment of the intravascular volume depletion by a small IVC diameter (<1 cm) with significant collapsibility (>50% with respiration) was comparable to the central venous pressure measured with an intravenous catheter with regards to the examination of cardiac function. Murthi et al. compared the cardiac index (CI) obtained by the focused rapid echocardiography evaluation (FREE) to other relevant invasive hemodynamic monitoring methods (pulmonary artery catheter and arterial pressure waveform-based device).⁵⁶ Their data suggested that patient management was frequently changed based on the data derived from FREE. Further, there was good agreement between the CIs obtained in FREE and a pulmonary artery catheter. Of interest, the role of point-of-care bedside ultrasound for unstable trauma patients has been evaluated in a randomized control trial.⁵⁷ In this study, the limited transthoracic echocardiogram (LTTE) was performed by trained non-cardiologists (trauma surgeon, emergency medicine physician, surgical, and emergency medicine residents) in the trauma bay. In the LTTE, fluid status, contractility, and pericardial effusion were reported. The use of the LTTE was associated with significantly less volume of intravenous fluid administered, less time to the operating room, and a higher rate of admission to the ICU. In a subgroup of patients with a traumatic brain injury, a significantly lower mortality rate was noted in the LTTE group (14.7% vs 39.5%, p = 0.03).

Ultrasound in Prehospital, Mass Casualty, and Military Settings

With recent advances in technology, currently used ultrasound machines are often portable. In special environments such as prehospital settings, mass casualty incidents, or with military care, a smaller size, hand-carried ultrasound machine can be used to make rapid diagnoses in trauma patients.^{58,59,60,61,62} One of the goals of ultrasound examination in the out-of-hospital setting is to help triage patients. Although a smaller machine is used, the quality of images should be equivalent to those obtained in the conventional FAST/E-FAST examination in the emergency department. This will facilitate detection of free fluid in the pericardial and intra-abdominal spaces and a hemothorax and pneumothorax. In addition, ultrasound has been used for the evaluation of other types of injuries to the eye and extremities.^63,64

The impact of the prehospital FAST (PFAST) examination on the management of patients with blunt abdominal trauma was evaluated in a multicenter prospective study from Germany.⁶⁵ In 95% of patients, the prehospital time was not prolonged because of the PFAST examination (mean time was 2.4 minutes) and good or acceptable quality images could be obtained to establish a diagnosis in 93% of patients. Compared with the FAST examination or CT performed in the emergency room, the PFAST examination had a sensitivity of 93%, a specificity of 99%, and an accuracy of 99%. A mass casualty incident is another unique situation that requires rapid and accurate triage of a large number of trauma victims. The use of ultrasound in a mass casualty incident was initially reported by Sarkisian et al. in the early 1990s.⁵⁹ Following the Armenian earthquake in 1988, ultrasound examinations identified trauma-related pathology in 51 of 400 patients screened. The average study time was 4 minutes with no false positive and four false negative cases. Zhou et al. reported a sensitivity of 91.9%, a specificity of 96.9%, and an accuracy of 96.6% in detecting any intra-abdominal injury from a more recent experience of surgeon-performed ultrasound in a Chinese earthquake.⁶²

Similarly, there are a few studies to show the feasibility of ultrasound use for the triage of wounded soldiers and civilians in the combat setting.^66,67 The FAST examination was performed in 281 patients during the 1-month period of the Second Lebanese War.⁶⁷ Sensitivity, specificity, and accuracy of the FAST examination to detect intraperitoneal free fluid were 76.5%, 98.4%, and 94.0% in soldiers and 67.6%, 95.2%, and 91.6% in civilians, respectively. As further developments in telemedicine are expected to improve the accuracy of the ultrasound examination in the field, images obtained there can be reviewed by physicians at a support hospital.⁶⁸

In addition to a thorough history and physical examination, ultrasound is frequently used in the management of patients with acute abdominal pain. It is particularly helpful when the consulting surgeon personally performs ultrasound imaging to expedite the diagnosis.

Acute Biliary Disease

For patients with abdominal pain in the RUQ, acute biliary disease is always listed as part of the differential diagnosis. Ultrasound examination of the RUQ area can visualize the majority of biliary structures including the gallbladder and bile duct. Although MDCT is frequently obtained for patients with acute abdominal pain, ultrasound is still considered the imaging modality of choice for patients with suspected acute biliary disorders.^69,70 The diagnostic criteria for acute cholecystitis consist of clinical signs, physical findings, and laboratory results in a guideline based on an international consensus meeting.⁷¹ Ultrasound or other imaging modalities are used to confirm the diagnosis (Table 16-6 and Fig. 16-15). The sensitivity and specificity of ultrasound for acute cholecystitis have been reported previously in multiple studies.^72,73,74 In 1994, a systematic review by Shea et al. documented an 88% sensitivity (95% confidence interval, 0.74–1.00) and 80% specificity (95% confidence interval, 0.62–0.98) in evaluating patients with suspected acute cholecystitis.⁷⁵ Nearly two decades later, Kiewiet et al. included cholescintigraphy and magnetic resonance imaging to compare the sensitivity and specificity of ultrasound with other imaging modalities.⁷⁶ In a head-to-head comparison, the sensitivity of ultrasound (80% vs 94%, p < 0.001) as well as specificity (75% vs 89%, p < 0.001) was significantly lower than with cholescintigraphy. Nonetheless, because of its availability, low cost, and low risk profile, ultrasound is practically the diagnostic modality of choice.

Acute Appendicitis

The diagnosis of appendicitis has improved with increased and appropriate use of imaging.⁷⁷ Recent data suggest that the negative appendectomy rate has significantly decreased from 23.0% to 1.7% while the preoperative CT rate increased from 1% to 97.5%.⁷⁸ Previous studies comparing ultrasound and MDCT for adult patients with suspected appendicitis showed comparable sensitivities and specificities.^79,80 Limitations of ultrasound examination include the following: (1) operator dependence; (2) decreased accuracy in patients with a thick abdominal wall or overlying bowel gas; and (3) inability to identify other associated pathology. Although MDCT is currently the most commonly obtained study for adult patients with suspected appendicitis, the use of ultrasound is still indicated for pediatric or pregnant patients to avoid radiation exposure or intravenous contrast dye. The sonographic findings to suggest acute appendicitis are listed in Table 16-7 and in Fig. 16-16).⁸¹

Pyloric Stenosis

Ultrasound is more frequently used to make a diagnosis of surgical disorders in the pediatric population than in adults. Nausea and vomiting in infants can be caused by serious intra-abdominal conditions requiring surgical intervention such as pyloric stenosis. In addition to a history of nonbilious projectile vomiting and a palpable “olive” on a physical examination, ultrasound is considered the imaging test of choice to confirm the diagnosis.^82,83 A target sign is seen in the transverse view, while the length and thickness of the pyloric muscle are measured in a longitudinal view of the upper abdomen (Fig. 16-17). A muscle thickness more than 3 mm and length more than 15 mm are considered abnormal, although there are variations in diagnostic criteria.⁸² Malcom et al. demonstrated the feasibility of the point-of-care ultrasound by nonradiologists to diagnose pyloric stenosis in their case series.⁸³

Soft Tissue Infection and Abscess

A superficial soft tissue infection can be easily detected on clinical examination. In contrast, an ultrasound examination can be used as an adjunct to visualize a deep space infection, particularly an abscess involving the deep subcutaneous tissue (breast, gluteal area) or muscle (Fig. 16-18). A high-frequency linear transducer is placed over the suspected area. The depth of imaging should be adjusted based on the location (eg, forearm vs thigh), so that a fluid collection (anechoic to hypoechoic area) will not be missed. Further, percutaneous aspiration or incision and drainage can be guided by ultrasound images.⁸⁴

As previously noted, the use of ultrasound in the ICU allows surgeons to supplement the findings on physical examination to make diagnoses without the need to transport a critically ill patient to another area of the hospital. Further, diagnostic and therapeutic ultrasound examinations are noninvasive, rapid, and readily repeatable. Once a diagnosis has been made, ultrasound may allow the surgeon to use invasive techniques under image guidance to provide a life-saving treatment. Ultrasound guidance and direct visualization during procedures performed by surgeons can lead to decreased complications, shorter hospital length of stay, and decreased cost.⁸⁵

Training programs that teach ultrasound skills in critical care to surgeons should be rigorous and include competence-based testing. Didactic training, hands-on experience, and a partnership with an echocardiography department are essential to training programs to develop advanced ultrasound skills. Surgeons should also have a continuing medical education program and formal certification and a credentialing process when developing ultrasound skills.^86,87,88,89

Hemodynamic Monitoring

Focused echocardiography (ECHO) performed by bedside clinicians can be useful for the assessment and management of hemodynamically unstable patients. Training surgeons with previously limited ultrasound skills in focused echocardiography is feasible, as this examination is goal-directed, problem-oriented, limited in scope, and simple compared to traditional echocardiography. Also, it allows for time-sensitive and repeated assessments. Focused echocardiography can be used to rapidly diagnose causes of hemodynamic instability and/or acute respiratory failure. A surgeon’s goal in performing cardiac ultrasound in a hemodynamically unstable patient is to assess global left and right ventricular (LV/RV) systolic function, intravascular volume status and preload responsiveness, and the presence of pericardial effusion/tamponade physiology. Additionally, left ventricular diastolic measurements/assessments are possible, unlike with other common monitoring devices (such as a pulmonary artery flotation catheter) and may be extremely helpful. Typically, focused echocardiographic measurements are either qualitative (ie, good vs poor) or semiquantitative based on measuring techniques with substantial extrapolations in computation.

Several variations of the focused ECHO technique have been described, and their utility has been examined in critically ill surgical patients.⁹⁰ The first, referred to as the Focus Assessed Transthoracic Echo (FATE) examination is a two-dimensional and M-mode imaging examination, consisting of the most basic cardiac and pleural views. Two derivative examinations have been described in the surgical literature. Gunst et al. developed a bedside ECHO protocol (the BEAT examination: Bedside Echocardiographic Assessment in Trauma/Critical Care) to be used for the hemodynamic assessment of patients in the surgical ICU.⁵⁴ Each letter of “BEAT” corresponds to a component of the examination (B: beat-cardiac index; E: effusion-pericardial effusion; A: area-subjective cardiac function; T: tank-volume status). In their study, the BEAT examination could be completed rapidly. Of 85 BEAT examinations performed by either surgical trainees or trauma surgeons, the images obtained for the cardiac index calculation were considered of good quality in approximately 60%. In the IVC images for assessment of preload, 97% were of good quality. The cardiac index in the BEAT examination was significantly correlated with that obtained from a pulmonary artery catheter.¹⁶

Similarly, the focused FREE examination has been used to monitor the hemodynamic status of patients in the surgical ICU. The examiner is able to obtain/calculate information regarding cardiac function, volume status, afterload, and anatomy. Despite the prevalence of thoracoabdominal surgery and mechanical ventilation in their cohort, FREE examiners were successful in completing the study.⁵⁶

Technique

Focused echocardiographic examinations are performed using a low-frequency cardiac transducer (small footprint) with the depth set to 14–16 cm for adequate visualization of the heart. If available, the cardiac software package and presets should be used as opposed to the abdominal software package that is commonly used in the FAST examination. Cardiac goal-directed ultrasound uses four main views as follows: (1) the subcostal view allows for visualization of IVC size/collapse, right ventricular and left ventricular size and pericardial effusions; (2) the parasternal long-axis view evaluates LV systolic function and presence of effusions; (3) the parasternal short-axis view allows visualization of LV function at the mid-left ventricle; and (4) the apical four-chamber view can demonstrate a pericardial effusion and RV size and function. In most cases, these four views can be obtained for patients in the supine position. More favorable images can be obtained by placing the patient in the left lateral decubitus position as the heart moves more closely to the chest wall. In some patients, only a single view may be possible, but, even in these instances, valuable information can be obtained.

The assessment of volume status and preload responsiveness is performed as a part of the cardiac examination. The latter is perhaps the more relevant parameter and represents whether a patient would benefit from volume administration (by increasing stroke volume and cardiac output). Assessment of volume status via echocardiography is typically performed by obtaining a static image of the structure of interest. Determination of preload responsiveness requires the use of dynamic imaging that entails a before and after assessment (relative to administration of fluid or inspiration or another maneuver) of the structure or parameter of interest. The most commonly used structure to determine volume status and preload responsiveness is the IVC. The diameter of the IVC is measured both at the end of inspiration and expiration phase in the subcostal view. For better representation of the relevant anatomy, a longitudinal view at the junction of the right atrium and the IVC is visualized first. The measurement is taken within a few centimeters of the cavoatrial junction. The volume status and preload responsiveness are estimated based on the static IVC diameter as well as the collapsibility during the respiratory cycle (Table 16-8). Other echocardiographic techniques of preload responsiveness exist and are beyond the scope of this chapter.

Cardiac function can be determined by both qualitative and quantitative means, the former unique to echocardiography. Qualitative assessment implies visualizing the beating heart and ascribing its function as normal or abnormal (more specifically, as increased, decreased or normal contractility). This skill is learned quickly and provides information on the cardiac ejection fraction that is not possible with more traditional methods of hemodynamic assessment, including the use of pulmonary artery catheters. Most often, the parasternal short-axis view is used to acquire qualitative information regarding contractility, morphology, size, and wall motion abnormality of the LV. The LV and RV are visualized simultaneously in the apical four-chamber views for the assessment of the right-sided cardiac function (Fig. 16-19). Normally, the RV size is two-third that of the LV. An enlarged RV can be the result of pressure or volume overload. Quantitative and semi-qualitative assessment of left-sided heart function provides actual values for either stroke volume (SV), ejection fraction (EF), or both using relatively simple methodologies.^54,56,90 Semi-quantitative methods utilize computational assumptions. Of three popular semi- or fully quantitative methods (fractional shortening, Simpson’s, and left ventricular outflow tract [LVOT]/velocity time integral [VTI] method) to estimate stroke volume (SV), the fractional shortening method was most significantly correlated with the data obtained from a pulmonary artery catheter in the aforementioned study of patients in the surgical ICU.⁹¹ In the fractional shortening method, a parasternal long-axis view is used for assessment of cardiac function. After an adequate view is obtained in 2D mode, the M-mode cursor is placed to visualize the LV at the level of the distal mitral valve (Fig. 16-20). End-diastolic and end-systolic diameters of the LV are measured in the M-mode image. SV can be calculated by applying these values into a formula stored in the cardiology presets of the ultrasound machine (Table 16-9). Similarly, cardiac index and ejection fraction are calculated, respectively. The fully quantitative methodology utilizing a measurement of LVOT and assessment of VTI is thought by others to be the most accurate; however, it requires acquisition of two cardiac views.⁹²

Pleural Ultrasound

The use of ultrasound for the detection of pleural-based diseases has some advantages over traditional radiographic imaging. Ultrasound is without radiation, easily portable, and provides real-time imaging. Pleural effusions are easily diagnosed and treated by surgeons using bedside ultrasound. As discussed previously in the trauma section, bedside thoracic ultrasound is more sensitive than a plain chest x-ray in detecting the presence of pleural fluid and distinguishing fluid from consolidation of the lung. During bedside thoracentesis to drain a pleural effusion in the ICU, ultrasound guidance increases the likelihood of a successful tap and reduces the risk of a pneumothorax.⁸⁵ A pneumothorax may occur in the ICU during mechanical ventilation or after invasive procedures such as a thoracentesis or insertion of a central venous catheter via the internal jugular or subclavian vein. A surgeon can use portable ultrasound to quickly diagnose the pneumothorax in the ICU in the same manner as described in the trauma section.^93,94 In supine and semi-erect views, an ultrasound is more sensitive than a chest x-ray (91% vs 50%), and both modalities provide similar specificities in the diagnosis of a pneumothorax.⁹⁵

Technique

Diagnosis and drainage of pleural effusions can be performed with the patient in the upright position, with the head of the bed elevated to at least a 45–60° angle. Patients who cannot tolerate sitting up can be imaged and/or drained supine with the ipsilateral arm positioned across the chest or in lateral decubitus position with the side of the suspected pleural effusion up. A 3.5–5.0-MHz convex array transducer is held perpendicular to the skin with the transducer marker pointed cephalad. The transducer is oriented to allow visualization between the ribs to identify pleural fluid. Once the targeted pleural fluid is imaged, a sterile field is prepared and a cover is placed on the ultrasound probe. The pleural space is entered with a large gauge needle while aspirating until pleural fluid is obtained. A guidewire is passed through the needle into the pleural cavity using the Seldinger technique. A small skin incision is made around the guidewire and a pigtail catheter is placed over the wire to allow drainage of the pleural fluid.

Pulmonary Ultrasound

Acute respiratory failure and insufficiency are critical conditions commonly encountered in the ICU. Making a rapid and accurate assessment of the underlining etiology is crucial as patient outcomes can be time-dependent. In the past, it was believed that ultrasound was not a useful tool to examine the lung as the air within the normal lung parenchyma prevents transmission of sound waves (Table 16-1). Recently, more data regarding the efficacy of ultrasound in the diagnosis of acute respiratory failure has been published.^96,97,98

Lichtenstein et al. incorporated several ultrasound findings into a decision tree to identify the cause of acute respiratory failure (Bedside Ling Ultrasound in Emergency: BLUE-protocol).⁹⁸ Using the algorithm, pulmonary etiologies of acute respiratory failure including parenchymal (eg, pneumonia, pulmonary embolism) or pleural lesions (eg, pneumothorax) were accurately identified in 90.5% of patients. The BLUE protocol starts with eliciting the aforementioned lung sliding sign (Fig. 16-11) which excludes a pneumothorax. In addition, A-lines (repetitive horizontal artifacts) can be identified in normal lung (A-profile). A pulmonary embolus should be considered as a cause of acute respiratory failure if venous thrombosis is associated with an A-profile. The B-line is another artifact characterized as a hyperechoic comet-tail arising from the pleural line. Lung rockets are defined as at least three B-lines in the intercostal space (Fig. 16-21). The combination of lung sliding and lung rockets (B-profile) favors conditions associated with pulmonary edema. Pneumonia can be diagnosed in several patterns of ultrasound findings including the following: (1) A-profile without associated venous thrombosis, positive posterolateral alveolar and pleural syndrome (PLAPS); (2) anterior lung consolidation (C-profile); and (3) lung rockets without lung sliding (B-profile). An A-profile without associated venous thrombosis or PLAPS suggests other pulmonary disorders including chronic obstructive pulmonary disease (COPD) or asthma. The utility of a lung ultrasound protocol has been prospectively evaluated in 189 patients on mechanical ventilation.⁹⁷ Sensitivities and specificities of the ultrasound examination for each pulmonary disease were as follows: cardiogenic pulmonary edema 97/95%, COPD or asthma 89/97%, pulmonary embolism 81/99%, pneumothorax 88/100%, and pneumonia 89/94%. Of 253 examinations, patient management was significantly changed in 119 (47%). Of note, a majority of these (81/119) required invasive interventions based on the diagnoses made by the ultrasound of the lung.

Insertion of a Central Venous Catheter

Insertion of a central venous catheter is performed frequently in critically ill patients. They are required for hemodynamic monitoring, volume resuscitation, administration of blood products, parenteral nutrition and medications, acquisition of lab specimens, and provision of renal replacement therapy.⁹⁹ Insertion can be associated with complications such as injury to surrounding vessels causing a hematoma and to the lung resulting in a hemothorax and/or pneumothorax. Ultrasound-guided insertion of a central venous catheter has been shown to decrease the number of attempts at venous cannulation, time required to successful insertion and the overall complication rate in randomized control studies.^100,101,102 A meta-analysis including 18 studies concluded that real-time ultrasound-guided cannulation of the internal jugular vein in adult patients was associated with a lower risk of overall cannulation failure (relative risk [RR] = 0.14, 95% CI = 0.06–0.33), complications (RR = 0.43, 95% CI = 0.22–0.87), reduced first attempt failure (RR = 0.59, 95% CI = 0.39–0.88), and reduced number of attempts (1.5 fewer attempts, 95% CI= 0.39–0.88) compared to the landmark technique.¹⁰³ Currently, the insertion of a central venous catheter into the internal jugular vein using ultrasound-guidance has become a recommended best practice due to its proven decrease in attempts and reduction in complications.¹⁰² In contrast, until recently, there were scarce data to support the use of ultrasound to guide cannulation of the subclavian vein.¹⁰³ Fragou et al. conducted a prospective randomized study which showed significantly improved outcomes associated with real-time ultrasound-guided cannulation compared to the landmark technique.¹⁰⁴ The success rate in the ultrasound group was 100% with a significantly shorter average access time (26.8 minutes vs 44.8 minutes, p < 0.05) and lower complication rates. As the subclavian vein is located posterior to the clavicle, the penetration of the ultrasound beam is often difficult. In this study, physicians rated the ultrasound-guided subclavian cannulation as a complex task (8 ± 0.2/10). Furthermore, ultrasound guided cannulation of the subclavian vein is more accurately referred to as an axillary approach.

Technique

The internal jugular vein in the cervical and upper thoracic region is imaged with a high-frequency linear transducer. Prior to preparation of the insertion site the targeted vein should be visualized with ultrasound. The transducer probe is placed transversely on the neck to obtain a cross-sectional image of the internal jugular vein and common carotid artery. The probe is then rotated 90° to obtain a longitudinal image. Patency of the vein should also be assessed by its ability to be easily compressed with the ultrasound transducer. During skin preparation and sterile draping of the insertion site the ultrasound probe is covered with a telescopically folded sterile sheath. The ultrasound transducer should be held in the nondominant hand perpendicular to the skin. The cannulating needle is held in the dominant hand and directed at the target vessel in real time. The tip of needle should be visualized in the image while the needle is being advanced. Once the vein is cannulated by the needle, the remainder of the procedure is completed using the Seldinger technique. The wire should be identified inside the jugular vein before dilating the tract (Fig. 16-22). Typically, the transverse view is used to identify puncture of the vessel, whereas the longitudinal view is beneficial to localize the needle tip and wire.

As the subclavian vein is close to bony structures, it is often challenging to visualize the anatomical relationship to the subclavian artery and pleural line. The axillary vein is the distal continuation of the subclavian vein and its cannulation under ultrasound-guidance can be more easily performed. Similar to imaging of the internal jugular vein, transverse and longitudinal images of the subclavian vein and artery are obtained before draping the area. The subclavian artery is normally located cephalad to the vein. Another key point in cannulation of the subclavian vein is to appreciate the proximity of the pleural line that can be within a few centimeters below the vein (Fig. 16-23).

Paracentesis

Abdominal paracentesis is a procedure that surgeons use in the ICU for diagnosis and/or therapy. Diagnostic paracentesis consists of obtaining a small amount of peritoneal fluid for culture to rule out infection and to characterize the fluid as a transudate or exudate. Therapeutic paracentesis is a technique that removes a large volume of ascites (typically in excess of 2 L) to reduce intra-abdominal pressure and treat the resulting abdominal discomfort and dyspnea. Therapeutic paracentesis is a procedure that is commonly performed by surgeons caring for patients with hepatic failure in the ICU setting who are at a high risk of postprocedure bleeding. Ultrasound guidance for paracentesis in patients with ascites results in greater success in acquiring fluid compared to traditional techniques, 95% versus 61%.¹⁰⁵ Patients undergoing ultrasound-guided paracentesis also have a decreased risk of bleeding, 0.27% versus 1.25% (without ultrasound) leading to decreased hospital length of stay and costs.⁸⁵

Technique

Paracentesis is typically performed with the patient supine with the needle inserted into the left lower quadrant. The general area of the puncture site is localized 2–3 cm medial and 2–3 cm cephalad to the anterior iliac spine in the left lower quadrant. A convex ultrasound of 3.5–5.0 MHz is then used to locate peritoneal fluid and to visualize the inferior epigastric artery to avoid injury and hemorrhage. Skin preparation and sterile draping of the area and use of the ultrasound probe is performed followed by insertion of the paracentesis needle. The paracentesis catheter is left in place to achieve removal of the desired diagnostic sample or to reduce intra-abdominal pressure.

It has been approximately 25 years since surgeons started to use ultrasound in the management of trauma patients. Currently, the FAST examination is most useful for patients with blunt trauma who have unstable vital signs. In patients with penetrating trauma to the chest, the pericardial component of the FAST examination is mandatory to rapidly diagnose a cardiac injury. In recent years thoracic ultrasound has been more frequently used to detect a pneumothorax, hemothorax/pleural effusion, and lung lesions both in the trauma bay and in the ICU. In the emergency department, the focused ultrasound examination is more frequently performed to evaluate patients with suspected intra-abdominal inflammatory processes.

Similarly, more advanced ultrasound techniques including echocardiography are now being used to guide the resuscitation of critically ill patients. Of note, these surgeon-performed ultrasound examinations are currently considered as standard care in many clinical settings.