Christopher J. Dente and Grace S. Rozycki
For nearly two decades, acute care surgeons have successfully performed, interpreted, and taught bedside ultrasound examinations of patients who are injured or critically ill.1–13 Real-time imaging allows the surgeon to receive instantaneous information about the clinical condition of the patient and, therefore, helps to expedite the patient’s management, which is important in patients with time-sensitive diagnoses. In many centers, ultrasound machines are owned by surgeons or surgical departments and are part of the standard equipment in the trauma resuscitation area as well as in the intensive care unit (ICU). While diagnostic peritoneal lavage (DPL) and computed tomography (CT) scanning are still valuable diagnostic tests for the detection of intra-abdominal injury in patients, ultrasound is not only faster but also noninvasive and painless.
As an extension of the physical examination, acute care surgeons routinely use ultrasound in the trauma setting to augment their physical examination in patients with suspected torso and extremity trauma, not only within the standard hospital resuscitation area but also in a variety of other locales. Additionally, ultrasound may be used to supplement the history and physical examination of nontrauma patients presenting with acute abdominal pain and a variety of other time-sensitive diagnoses in the emergency department. Finally, ultrasound may be used in the ICU in a variety of ways to facilitate procedures, detect complications, and augment a surgeon’s physical examination.
As such, this chapter begins with a basic introduction to select principles of ultrasound physics and then covers the components, indications, and pitfalls of the common, focused ultrasound examinations used by acute care surgeons who are evaluating trauma patients, nontrauma patients presenting with acute symptoms, and, finally, critically ill patients in the ICU.
Ultrasonography is operator dependent and, therefore, an understanding of select principles of ultrasound imaging is necessary so that images may be acquired rapidly and interpreted correctly. Knowledge of some 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 to 16-3.
TABLE 16-1 Ultrasound Physics Terminology Relevant to Ultrasound Imaging
TABLE 16-2 Essential Principles of Ultrasound
TABLE 16-3 Terminology Used in Interpretation of Ultrasound Images
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.14,15 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 left to right. 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. 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 and the projected patient positions on the ultrasound monitor are shown in Fig. 16-1.16
TABLE 16-4 Scanning Planes Used in Ultrasound Imaging16
FIGURE 16-1 Scanning planes used in ultrasound imaging. (Adapted with permission from Tempkins BB. Scanning Planes and Methods. Ultrasound Scanning: Principles and Protocols. Philadelphia, PA: WB Saunders Company; 1993, © Elsevier.)
Although diagnostic ultrasound uses transducer frequencies ranging from 1 MHz (megahertz = 1 million cycles/s) to 30 MHz, 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 an abscess in the soft tissue of an extremity. Lower-frequency transducers emit waves that penetrate deeply into the tissue and, therefore, are preferred for visualizing organs such as the liver or spleen.14,17,18 Tips to maximize accuracy and quality of ultrasound imaging relative to the above-mentioned physics principles are listed in Table 16-6.
TABLE 16-5 Clinical Applications of Selected Transducer Frequencies
TABLE 16-6 Maximizing Accuracy in Ultrasound Imaging
SURGEON-PERFORMED ULTRASOUND IN TRAUMA
Developed for the evaluation of injured patients, the Focused Assessment for the Sonographic Examination of the Trauma Patient (FAST) is a rapid diagnostic examination to assess patients with potential injuries to the torso. The test sequentially surveys for the presence or absence of fluid in the pericardial sac and in the dependent abdominal regions, including Morison’s pouch region in the right upper quadrant (RUQ), the left upper quadrant (LUQ) behind the spleen and between the spleen and kidney, and the pelvis posterior to the bladder. Surgeons can perform the FAST during the primary or secondary survey of the American College of Surgeons Advanced Trauma Life Support19algorithm and, although minimal patient preparation is needed, a full urinary bladder is ideal to provide an acoustic window for visualization of blood in the pelvis.
Blood, as any fluid, will accumulate in dependent regions of the abdomen.20 In the supine position, this corresponds to Morison’s pouch, the splenorenal recess, and above the spleen as well as in the pelvis posterior to the bladder. All these regions may be visualized rapidly and dependably with the FAST. Furthermore, ultrasound is an excellent modality for the detection of intra-abdominal fluid, having been shown to detect ascites in small amounts.21,22Although the exact minimum amount of intraperitoneal fluid that can be detected by ultrasound is not known,23 most authors agree that it is a sensitive modality.
The FAST is performed in a specific sequence for several reasons. The pericardial area is visualized first so that blood within the heart can be used as a standard to set the gain (Table 16-1). Most modern ultrasound machines have presets so that the gain does not need to be reset each time the machine is turned on. Occasionally, if multiple types of examinations are performed with different transducers, the gain should be checked to ensure that intracardiac blood appears anechoic. This maneuver ensures that a hemoperitoneum will also appear anechoic and will be readily detected on the ultrasound image. The abdominal part of the FAST begins with a survey of the RUQ that is the location within the peritoneal cavity where blood most often accumulates and is most readily detected with the FAST. Indeed, investigators from four Level I trauma centers examined true-positive ultrasound images of 275 patients who sustained either blunt (#220) or penetrating (#55) injuries.24 They found that regardless of the injured organ (with the exception of those patients who had an isolated perforated viscus), blood was most often identified on the RUQ image of the FAST. This can be a time-saving measure because when hemoperitoneum is identified on the FAST examination of a hemodynamically unstable patient, that image alone, in combination with the patient’s clinical picture, is sufficient to justify an immediate abdominal operation.24 In a stable patient, following the exam of the RUQ, the LUQ and pelvis are visualized as discussed below.
Ultrasound transmission gel is applied on four areas of the thoracoabdomen, and the examination is conducted in the following sequence: the pericardial area, RUQ, LUQ, and the pelvis (Fig. 16-2).
FIGURE 16-2 Schematic diagram of transducer positions for FAST: pericardial, right upper quadrant, left upper quadrant, and pelvis.
A 3.5-MHz convex transducer is oriented for sagittal or longitudinal views and positioned in the subxiphoid region to identify the heart and to examine for blood in the pericardial sac. The normal and abnormal views of the pericardial area are shown in Fig. 16-3. The subxiphoid image is usually not difficult to obtain, but a severe injury to the chest wall, a very narrow subcostal area, subcutaneous emphysema, or morbid obesity can prevent a satisfactory examination.25 Both of the latter conditions are associated with poor imaging because air and fat reflect the wave too strongly and prevent penetration into the target organ.14 If the subcostal pericardial image cannot be obtained or is suboptimal, a parasternal ultrasound view of the heart should be performed (Figs. 16-4 and 16-5).
FIGURE 16-3 (Left) Sagittal view of pericardial area showing pericardium as single echogenic line (normal). (Right) Sagittal view of pericardial area showing separation of visceral and parietal areas of pericardium with blood (arrow) that appears anechoic.
FIGURE 16-4 Transducer position for left parasternal view of heart.
FIGURE 16-5 Normal (left) and abnormal (right) heart, parasternal view.
Next, the transducer is placed in the right anterior or midaxillary line between the 11th and 12th ribs to obtain sagittal images of the liver, kidney, and diaphragm (Fig. 16-6) and determine the presence or absence of blood in Morison’s pouch and in the right subphrenic space. Next, attention is turned to the LUQ. With the transducer positioned in the left posterior axillary line between the 10th and 11th ribs, the spleen and left kidney are visualized and the presence or absence of blood between the two organs and in the left subphrenic space is determined (Fig. 16-7). The splenic window is often the most difficult window to adequately visualize and the probe should be placed significantly more posterior (posterior axillary line) and superior (one to two rib spaces higher) than with the RUQ window.
FIGURE 16-6 (A) Normal sagittal view of liver, kidney, and diaphragm. Note Gerota’s fascia is hyperechoic. (B) Abnormal sagittal view of liver, kidney, and diaphragm. Note fluid (blood) in between liver and kidney (arrows).
FIGURE 16-7 (Left) Normal sagittal view of spleen, kidney, and diaphragm. (Right) Abnormal sagittal view of spleen, kidney, and diaphragm with fluid (blood) in between spleen and kidney and above the spleen in the subphrenic space.
Finally, the transducer is directed for a transverse view and placed about 4 cm superior to the symphysis pubis. It is slowly swept inferiorly to obtain a coronal view of the full bladder and the pelvis examining for the presence or absence of blood (Fig. 16-8).
FIGURE 16-8 (Left) Normal coronal view of full urinary bladder. (Right) Abnormal coronal view of full bladder with fluid in pelvis. (Note the bowel floating in fluid.)
Accuracy of the FAST
Improper technique, inexperience of the examiner, and inappropriate use of ultrasound have long been known to adversely impact the accuracy of ultrasound imaging. More recently, the etiology of injury, the presence of hypotension on admission, and select associated injuries have also been shown to influence the accuracy of this modality.2,3,8 Failure to consider these factors has led to inaccurate assessments of the accuracy of the FAST by comparing it inappropriately to a CT scan and not recognizing its role in the evaluation of patients with penetrating torso trauma.26,27 Both false-positive and -negative pericardial ultrasound examinations have been reported to occur in the presence of a massive hemothorax or mediastinal blood.4,8,10,28 Repeating the FAST after the insertion of a tube thoracostomy improves the visualization of the pericardial area and decreases the number of false-positive and -negative studies. While false studies may occur, a rapid focused ultrasound survey of the subcostal pericardial area is a very accurate method to detect hemopericardium in most patients with penetrating wounds in the “cardiac box.”4,10 In a large study of patients who sustained either blunt or penetrating injuries, the FAST was 100% sensitive and 99.3% specific for detecting hemopericardium in patients with precordial or transthoracic wounds. Furthermore, the use of pericardial ultrasound has been shown to be especially helpful in the evaluation of patients who have no overt signs of pericardial tamponade. This was highlighted in a study in which 10 of 22 patients with precordial wounds and a hemopericardium on an ultrasound examination had admission systolic blood pressures >110 mm Hg and were relatively asymptomatic. Based on these signs and the lack of symptoms, it is unlikely that the presence of cardiac wounds would have been strongly suspected in these patients and, therefore, this rapid ultrasound examination provided an early diagnosis of hemopericardium before the patients underwent physiologic deterioration.
The FAST is also very accurate when it is used to evaluate hypotensive patients who present with blunt abdominal trauma. In this scenario, ultrasound is so accurate that when the FAST is positive, an immediate operation is justified.4,8,10,29
Because the FAST is a focused examination for the detection of blood in dependent areas of the abdomen, its results should not be compared to those of a CT scan because the FAST does not readily identify intraparenchymal or retroperitoneal injuries. Therefore, select hemodynamically stable patients considered to be at high risk for occult intra-abdominal injury should undergo a CT scan of the abdomen regardless of the results of the FAST examination. These patients include those with fractures of the pelvis or thoracolumbar spine, major thoracic trauma (pulmonary contusion, lower rib fractures), and hematuria. These recommendations were based on the results of two studies by Chiu et al. in 199730 and Ballard et al. in 1999.31 Chiu et al. reviewed their data on 772 patients who underwent FAST examinations after sustaining blunt torso injury. Of the 772 patients, 52 had intra-abdominal injury but 15 of them had no hemoperitoneum on the admitting FAST examination or on the CT scan of the abdomen. In other work conducted by Ballard et al. at Grady Memorial Hospital, an algorithm was developed and tested over a 3.5-year period to identify patients who were at high risk for occult intra-abdominal injuries after sustaining blunt thoracoabdominal trauma.31 Of the 1,490 patients admitted with severe blunt trauma, there were 102 (70 with pelvic fractures, 32 with spine injuries) who were considered to be at high risk for occult intra-abdominal injuries. Although there was only 1 false-negative FAST examination in the 32 patients who had spine injuries, there were 13 false negatives in those with pelvic fractures. Based on these data, the authors concluded that patients with pelvic fractures should have a CT scan of the abdomen regardless of the result of the FAST examination. The lower accuracy of the FAST in patients with pelvic fractures was again noted in a recent series published by Friese et al., in which an initial FAST examination had an 85% positive predictive value but only a 63% negative predictive value in 146 patients with pelvic fractures.32 These studies have helped provide guidelines to decrease the number of false-negative FAST studies, but, as with the use of any diagnostic modality, it is important to correlate the results of the test with the patient’s clinical picture. Suggested algorithms for the use of FAST are depicted in Fig. 16-9A and B. Indeed, the FAST exam has been included in the most recently published evidence-based guidelines for the evaluation of patients with blunt abdominal trauma from the Eastern Association for the Surgery of Trauma (EAST) with reported accuracy rates of 96–98%.33
FIGURE 16-9 (A) Algorithm for the use of ultrasound in patients with penetrating chest wounds. (B) Algorithm for the use of ultrasound in patients with blunt abdominal trauma.
Quantification of Blood
The amount of blood detected on the abdominal CT scan34 or in the DPL aspirate (or effluent) has been shown to predict the need for operative intervention.35 Similarly, the quantity of blood that is detected with ultrasound may be predictive of a therapeutic operation.36,37 Huang et al. developed a scoring system based on the identification of hemoperitoneum in specific areas such as Morison’s pouch or the perisplenic space.36 Each abdominal area was assigned a number from 0 to 3, and the authors found that a total score of ≥3 corresponded to more than 1 L of hemoperitoneum. This scoring system had a sensitivity of 84% for determining the need for an immediate abdominal operation. Another scoring system developed and prospectively validated by McKenney et al. examined the patient’s admission blood pressure, base deficit, and the amount of hemoperitoneum present on the ultrasound examinations of 100 patients.37 The hemoperitoneum was categorized by its measurement and its distribution in the peritoneal cavity, so that a score of 1 was considered a minimal amount of hemoperitoneum but a score of >3 signified a large hemoperitoneum. Forty-six of the 100 patients had a score >3, and 40 (87%) of them underwent a therapeutic abdominal operation. This scoring system had a sensitivity, specificity, and accuracy of 83%, 87%, and 85%, respectively. The authors concluded that an ultrasound score of >3 is statistically more accurate than a combination of the initial systolic blood pressure and base deficit for determining which patients will undergo a therapeutic abdominal operation. Although the quantification of hemoperitoneum is not exact, it can provide valuable information about the need for an abdominal operation as well as its potential to be therapeutic.
Recent Advances and Organ Specificity
As surgeons have become more facile with ultrasound exams and as technology has improved, extensions of the FAST exam have been described. Again, it is noted that the standard FAST exam is designed to accurately answer two simple questions: Is there fluid in the peritoneal cavity and is their fluid in the pericardial sac? The use of ultrasound for more complex diagnostic interventions is described below, but these areas are less well studied and beyond the purview of the traditional FAST exam.
A more recent prospective, multicenter trial conducted by the Western Trauma Association reported on the use of ultrasound to serially evaluate patients with documented solid organ injuries (SOI) after trauma.38 The so-called BOAST exam, or the bedside organ assessment with sonography after trauma, was performed by a limited number of experienced surgeon sonographers in 126 patients with 135 SOI in 4 American trauma centers. This study, performed over nearly 2 years, was designed to be a more thorough abdominal ultrasound examination with multiple views obtained of each solid organ (kidneys, liver, and spleen). Criteria for enrollment included normal hemodynamics, absence of peritonitis or other need for urgent laparotomy, and lack of excessive blood transfusion in the attending physician’s judgment. All patients were victims of blunt trauma with a mean Injury Severity Score (ISS) of nearly 15.
Overall, only 34% of injuries to solid organs were seen with BOAST yielding an error rate of 66%. None of the 34 grade I injuries were identified and only 13 (31%) of the grade II injuries were identified. Sensitivities for grade III and IV injuries ranged from 25% to 75% and only one grade V injury (to the liver) was examined and positively identified. Eleven patients developed 16 intra-abdominal complications (8 pseudoaneurysms, 4 bilomas, 3 abscesses, and 1 necrotic organ), and 13 (81%) were identified by the sonographers. This study emphasizes that ultrasound, in most surgeons’ hands, should not be considered a reliable modality for diagnosis and grading of SOI although it may be acceptably accurate in the diagnosis of post-traumatic abdominal complications in patients with SOI managed nonoperatively.
In Europe, preliminary work using Power Doppler ultrasonography to identify specific organ injuries has been published in recent years.39,40 Many of these exams include the use of a sonographic contrast agent injected peripherally during the scan. In one study, the authors were able to document extravasation of contrast in 20 of 153 patients (13%). Extravasation was seen not only from the spleen, liver, and kidney after trauma but also in postoperative patients (aortic aneurysm repair, postsplenectomy) and in a patient with a ruptured aortic aneurysm. In 9 of 20 patients, CT scan was performed and all 9 confirmed extravasation of contrast. In the 133 patients without extravasation, the absence of active bleeding was inferred by a subsequent CT scan in 82 patients, surgical data in 13 patients, and clinical follow-up in 38 patients, with no cases of active bleeding missed by ultrasound. Thus, the addition of an ultrasonic contrast agent and Power Doppler may be of some benefit in the diagnosis of specific injuries. It should be emphasized, however, that the FAST exam in most American trauma centers is used simply as a screening tool to identify the presence or absence of hemoperitoneum or hemopericardium in a trauma patient.
A focused thoracic ultrasound examination was developed by surgeons to rapidly detect the presence or absence of a traumatic hemothorax in patients during the ATLS secondary survey.9 This focused thoracic ultrasound examination employs the ultrasound physics principles of the mirror image artifact and tissue acoustic impedance as presented in Table 16-1. A test that promptly detects a traumatic effusion or hemothorax is worthwhile because it dramatically shortens the interval from the admission of the patient with hemothorax to the insertion of a thoracostomy tube.
The technique for this examination is similar to that used to interrogate the upper quadrants of the abdomen in the FAST and also uses the same type and frequency transducer. In point of fact, it is performed one to two rib spaces higher than the RUQ and LUQ FAST views using the same probe. Ultrasound transmission gel is applied to the right and left lower thoracic areas in the midaxillary to posterior axillary line between the 9th and 10th intercostal spaces (Fig. 16-10). The transducer is slowly advanced cephalad to identify the hyperechoic diaphragm and to interrogate the supradiaphragmatic space for the presence or absence of fluid (Fig. 16-11A and B) that appears anechoic. In the positive thoracic ultrasound examination, the hypoechoic lung can be seen “floating” amidst the fluid. The same technique can be used to evaluate a critically ill patient for a pleural effusion as discussed earlier.
FIGURE 16-10 Transducer positions for thoracic ultrasound examination (detection of hemothorax).
FIGURE 16-11 (A) Sagittal view of liver, kidney, and diaphragm. Note supradiaphragmatic (lung) area but absence of pleural effusion. (B) Sagittal view of right supradiaphragmatic space. The right hemithorax contains fluid (blood) that appears anechoic.
One of the earliest reports on the use of ultrasound for the evaluation of fluid collections in the pleural space was described by Joyner et al. in 1967.41 Later, Gryminski et al. documented the superiority of ultrasound over standard radiography for the detection of pleural fluid.42 In that study, they reported that ultrasound detected even small amounts of pleural fluid in 74 (93%) of 80 patients, whereas plain radiography detected pleural fluid in only 66 (83%) of these patients.
Surgeons at Emory University have also examined the accuracy of this examination in 360 patients with blunt and penetrating torso injuries.9 They compared the time and accuracy of ultrasound with that of the supine portable chest x-ray and found both to be very similar with 97.4% sensitivity and 99.7% specificity observed for thoracic ultrasound versus 92.5% sensitivity and 99.7% specificity for the portable chest x-ray. Performance times, however, for the thoracic ultrasound examinations were statistically much faster than those for the portable chest x-ray. Although it is not recommended that the thoracic ultrasound examination replace the chest x-ray, its use can expedite treatment in many patients and decrease the number of chest radiographs obtained.
The use of ultrasound for the detection of a traumatic pneumothorax is not a new diagnostic test, having been reported by numerous acute care surgeons dating back to the early 1990s.43–47 This examination is useful to the surgeon to evaluate a patient for a potential pneumothorax in the following circumstances: (1) bulky radiology equipment is not readily available; (2) inordinate delays for obtaining a chest x-ray are anticipated; or (3) numerous injured patients (mass casualty situation) must be rapidly assessed and triaged.48,49 Although useful in the trauma resuscitation area, surgeons may also find this examination helpful to detect a pneumothorax in a critically ill patient who is on a ventilator, after a thoracentesis procedure, or, potentially, after discontinuing the suction on an underwater seal device.
A 5.0- to 7.5-MHz linear array transducer is used to evaluate a patient for the presence of a pneumothorax. The examination may be performed while the patient is in the erect or the supine position. Ultrasound transmission gel is applied to the right and left upper thoracic areas at about the third to fourth intercostal space in the midclavicular line and the presumed unaffected thoracic cavity is examined first. The transducer is oriented for longitudinal imaging, is placed perpendicular to the ribs, and is slowly advanced medially toward the sternum and then laterally toward the anterior axillary line. The normal examination of the thoracic cavity identifies the rib (seen as black on the ultrasound image because it is a refraction artifact), pleural sliding, and a comet tail artifact (Table 16-1). Pleural sliding is the identification of the visceral and parietal layers of the lung seen as hyperechoic superimposed pleural lines. When a pneumothorax is present, air becomes trapped between the visceral and parietal pleura and does not allow for the transmission of the ultrasound waves. Therefore, the visceral pleura is not imaged and pleural sliding is not observed. The comet tail artifact is generated because of the interaction of two highly reflective opposing interfaces, that is, air and pleura (Fig. 16-12). When air separates the visceral and parietal pleurae, the comet tail artifact is not visualized. If desired, the examination may be repeated with the transducer oriented for transverse views, with images obtained with the probe parallel to the ribs.
FIGURE 16-12 Comet tail artifact (arrow).
Several studies have documented excellent sensitivity and specificity of ultrasound for the detection of a pneumothorax in the resuscitation area.43,45,46,50 Dulchavsky et al. from Detroit Receiving Hospital, Wayne State University, showed that ultrasound can be successfully used by surgeons to detect a pneumothorax in injured patients.51 Of the 382 patients (364 trauma; 18 spontaneous) evaluated with ultrasound, 39 had pneumothoraces and ultrasound successfully detected 37 of them, yielding a 95% sensitivity. Not unexpectedly, pneumothoraces in two patients could not be detected because of the presence of significant subcutaneous emphysema. The authors recommended that when a portable chest x-ray cannot be readily obtained, the use of this bedside ultrasound examination for the identification of a pneumothorax can expedite the patient’s management.
One study, published in 2006, however, documents significant loss of accuracy of an ultrasound examination starting about 24 hours after chest tube insertion.52 This study documents the hospital course of 14 patients with tube thoracostomies undergoing 126 ultrasound examinations over their hospital course. While ultrasound detection of pleural sliding in uninstrumented pleural cavities remained 100% accurate over time, the accuracy of ultrasound examination after chest instrumentation fell to 65% after 24 hours.52 It was theorized that adhesion formation led to false-positive examinations, in that normal pleural sliding was unable to be appreciated in patients with lung adhesions. This point illustrates the subtle difference in the usefulness of the ultrasound examination for pneumothorax: a “positive” examination is related to the absence of a normal finding (pleural sliding) rather than the presence of abnormal finding (i.e., fluid within the peritoneal cavity after blunt abdominal trauma). Thus, other causes of the loss of sliding (i.e., adhesion formation) can cause a false-positive and misleading examination. Indeed, a review of the literature revealed studies in animal models in which significant adhesion formation occurred as early 24 hours after thoracotomy.53 This same study also noted that the rapidity and degree of adhesion formation not only was variable based on the type and degree of injury but also varied within animals with similar injuries.53 Thus, one should be cautious when interpreting ultrasound examinations in patients with acute or chronic evidence of chest manipulation as false-positive studies may occur.52
Fractures of the sternum are visualized on a lateral x-ray view of the chest, but this film may be difficult to obtain in a patient with multiple injuries. For this reason, an ultrasound examination of the sternum can rapidly detect a fracture while the patient is still in the supine position and, therefore, avoid the need to obtain a lateral x-ray.54
The ultrasound examination of the sternum is performed using a high-frequency (>5.0 MHz) linear array transducer that is oriented for sagittal (longitudinal) views. Ultrasound transmission gel is applied over the sternal area while the patient is in the supine position. Beginning at the suprasternal notch, the transducer is slowly advanced in a caudad direction to interrogate the bone for a fracture. The examination is then repeated with the transducer oriented for transverse views. The examination of the intact sternum is shown in Fig. 16-13. A sternal fracture is identified on the ultrasound examination as a disruption of the cortical reflex (Fig. 16-14). Investigators have found that the use of ultrasound for this diagnosis is more accurate (and much more rapid) than a lateral x-ray view of the chest.54
FIGURE 16-13 Sagittal view of sternum. Normal findings.
FIGURE 16-14 Sagittal view of sternum illustrating fracture (interruption of hyperechoic line).
Ultrasound in the Pregnant Trauma Patient
Ultrasound would seem to be an ideal method of evaluating a pregnant patient with suspected blunt abdominal trauma as it is portable, noninvasive, and free of ionizing radiation. The Advanced Trauma Life Support course teaches that unrecognized abdominal trauma is a major problem in the pregnant trauma patient.19 Concerns over changes in abdominal anatomy leading to difficulty in obtaining images have not borne out in objective evaluations. Goodwin et al.55 reported on their 8-year experience with the FAST exam in 127 pregnant patients, including 5 of 6 patients with hemoperitoneum who were found to have fluid on the FAST exam (sensitivity 83%). Of the 120 without abdominal injury, 117 had a true-negative FAST (specificity 98%), with three false-positive exams due to serous intraperitoneal fluid. Furthermore, Brown et al.56 reported on their experience with a more extensive ultrasound exam in 101 stable, pregnant patients with suspected blunt abdominal trauma. Median gestational age was just over 24 weeks, and these patients underwent an official abdominal ultrasound by a certified technician to include images of the fetus and placenta. The sensitivity was 80% (four of five patients had correct identification of injuries) with one missed placental hematoma that required an emergent cesarean delivery for fetal distress. Injuries identified included one placental abruption, two splenic lacerations, one hepatic laceration, and one renal injury. None of the 96 patients with a negative ultrasound had injuries discovered later in their hospital course (specificity 100%). Thus, it would seem that ultrasound remains a good screening tool for the pregnant patient with blunt abdominal trauma and has the advantages of repeatability and a lack of radiation exposure.
Ultrasound in Penetrating Trauma
Ultrasound for the diagnosis of injuries after penetrating trauma has been studied much less extensively than ultrasound used after blunt trauma. Several of the larger, well-known series4,9,10 have included patients with penetrating trauma and, as stated previously, ultrasound of the pericardium has been shown to be accurate for diagnosis of injury in patients with penetrating injury to the “cardiac box.”9 In a recent study of 32 patients with penetrating anterior chest trauma, ultrasound was used to diagnose 8 pericardial effusions with a reported 100% accuracy (8 true-positive and 24 true-negative exams).57 Eight other patients were noted to have intraperitoneal fluid and underwent therapeutic exploration including repair of five diaphragmatic injuries, three hepatic lacerations, three splenic lacerations, three gastric injuries, two injuries to the small bowel, and one injury to the adrenal gland. No false-positive or false-negative examinations of the peritoneum were reported. Other studies have shown that the accuracy of FAST after penetrating trauma is somewhat less with one study reporting a sensitivity for abdominal injury after penetrating trauma as low as 67%.58
A recent report by Murphy et al. looked at the utility of ultrasound to diagnose fascial penetration after anterior abdominal stab wounds.59 In this study, 35 patients underwent ultrasonic evaluation of their anterior abdominal fascia with an 8.0-MHz linear array probe followed by a local wound exploration. While ultrasound had only a 59% sensitivity (13/22 patients), it did have a 100% specificity with no false-positive studies. Thus, if fascial penetration is noted on ultrasound, a more invasive wound exploration is probably not needed; however, a negative ultrasound evaluation is clearly less helpful and does not preclude peritoneal penetration.
Ultrasound in Pediatric Trauma Patients
Ultrasound as a modality would seem to be attractive for use in a pediatric population for many of the same reasons that have already been elaborated upon, including the lack of radiation exposure and the noninvasive nature of the examination. Many of the early studies in the pediatric literature regarding the use of ultrasound after trauma involved studies performed by radiologists or sonographers.27,60,61However, there are now several studies of surgeon-performed FAST examinations that show similar sensitivities, specificities, and accuracies as in the adult population.62–64 For example, in a series by Soundappan et al.,64 FAST examination had a sensitivity of 81%, a specificity of 100%, and an accuracy of 97% in a group of 85 pediatric patients who were victims of blunt abdominal trauma. Thus, while the literature is not as robust as in the adult population, the use of surgeon-performed ultrasound in the pediatric trauma bay is becoming much more widespread.
Ultrasound in Austere Settings
Ultrasound on Deployment
The portability of ultrasound makes it ideal for use in forward settings. Training courses are in place to teach the use of the FAST exam to military surgeons, and handheld ultrasound is now routinely deployed within the British Defence Medical Services.65 Indeed, in a survey of surgeons reviewing potential preventable casualties in Vietnam, ultrasound was the fourth most commonly mentioned advancement in technology (behind modern ventilators, CT scanners, and modern antibiotics) that may have assisted in better patient salvage.66
Although up to 90% of war wounds are penetrating, ultrasound may allow quicker, more accurate triage decisions as patients with penetrating abdominal trauma with no or minimal hemoperitoneum may be transferred to the next echelon where the study may be repeated or additional diagnostic maneuvers undertaken.67 In a study from the Croatian conflict in 1999, FAST was shown to have a sensitivity of 86%, a specificity of 100%, and an accuracy of 97% when applied to 94 casualties evaluated over a 72-hour period. This was comparable to the accuracy achieved by the authors in their civilian experience with FAST in more than 1,000 patients over the 3 years prior to the conflict. In a somewhat recent small series,67 FAST was used with excellent results in a British military hospital in Iraq. Fifteen casualties were evaluated with serial FAST exams, and 14 had negative exams at admission and again at 6 hours. One patient underwent laparotomy based on trajectory and had no intraperitoneal fluid but two small holes were discovered in the cecum that required repair. The other 13 patients recovered without sequelae. One exam was positive and led to immediate laparotomy in a patient with a grade V liver injury after a motor vehicle collision.
Because ultrasound is portable enough to use in active combat situations, research is ongoing to evaluate the best method to teletransmit images obtained in the field. Several different satellite transmission systems have been evaluated, and high-quality images were able to be obtained in the majority of cases; however, the balance between the weight of the system and the minimum image quality has still not been completely achieved.67 It has been noted that images can be transmitted from up to 1,500 ft from the antennae without significant degradation.68 As technology advances, one would expect imaging systems to continue to become smaller and lighter with improved image quality, making ultrasound even more appealing as a modality for use in the forward setting.
Ultrasound in Space
Many of the same qualities that make ultrasound appealing for use in combat make it equally appealing as a diagnostic modality in space, where an injury might mandate abortion of a multimillion dollar mission. Indeed, ultrasound is one of the only feasible diagnostic modalities on space missions, given size and weight restrictions. Also, ultrasound examinations are easily taught and images can be relayed with minimal delay to physicians on the ground. ATLS procedures are also feasible in space,69 and lifesaving procedures could be performed based on ultrasound findings.
Ultrasound has been used in space for several decades. Indeed, it has been ultrasound technology that has taught us much about the physiologic effects of microgravity, especially the fluid shifts associated with space travel.70 As early as 1982, cardiac ultrasound was used to evaluate left ventricular systolic function and cardiac chamber size in cosmonauts. The first American ultrasound system in space was the American flight echograph from Advanced Technology Laboratories (Bothel, WA) that first flew in 1984 and eventually was capable of three-dimensional images using a tilt frame device. Currently, the Human Research Facility aboard the International Space Station is equipped with a state-of-the-art Philips HDI 5000 (Philips Medical, Bothel, WA).70
Because surface tension and capillary action are the principal physical forces in space, scientists questioned whether images obtained on the standard FAST exam would be useful in microgravity. There are now several published studies of ultrasounds performed on parabolic flights in the NASA Microgravity Research Facility, a KC-135 aircraft. This aircraft can generate 25- to 30-second intervals of weightlessness using serial parabolic trajectories. A porcine model of intra-abdominal hemorrhage was created on the ground and studied during parabolic flights.71 Over 2,000 ultrasound segments were recorded with 80% of these considered feasible for diagnosis of the presence or absence of abdominal fluid. The sonographers felt the exam was no more difficult than one done on the ground as long as the sonographer and patient were adequately restrained. For the intraperitoneal portion of the exam, a fourth view (the midline “abdominal sweep”) was added and, with this addition, the FAST exam was able to reliably detect even relatively small amounts of intraperitoneal fluid. The Morison’s pouch view remained the most sensitive window for fluid detection.71 Further study using a similar model revealed that ultrasound can also reliably detect both hemothorax and pneumothorax in microgravity.72
Recently, astronauts aboard the International Space Station performed FAST ultrasounds that were transmitted with a 2-second satellite delay to directors on the ground, who were able to provide them with real-time instructions for probe position and system adjustments. Exams were able to be completed in roughly 5 minutes with adequate images obtained in all views.73 Astronauts have also been able to perform comprehensive ocular ultrasounds with the same real-time feedback.74
In summary, ultrasound fulfills all the necessary criteria for a diagnostic modality in space. It is sufficiently portable, teletransmittable, teachable, and accurate. It will likely continue to be the only feasible technology to assist with medical diagnoses on space missions in the near future.
SURGEON-PERFORMED ULTRASOUND IN ACUTE SURGICAL DISORDERS
Given the acceptance of surgeon-performed ultrasound in the trauma setting, as described above, it is only logical for surgeons to build on their experience and extend the use to other aspects of acute care surgery, including the evaluation of the stable and unstable patients with acute abdominal pain.
Evaluation of the Stable Patient with Acute Abdominal Pain
While there remains no substitute for an adequate and accurate history and physical examination, an ultrasound examination may provide additional information that helps a surgeon determine the patient’s need for urgent intervention. While ultrasound imaging has several uses in the stable patient with abdominal pain, it is likely most useful for the assessment of patients with RUQ pain.
In a patient with RUQ pain, ultrasound can demonstrate the presence or absence of gallstones, an abnormally thickened gallbladder wall, sludge within the gallbladder, or a dilated common bile duct. The presence of these sonographic signs of gallbladder disease, combined with the patient’s clinical condition, provides the surgeon with immediate information that may narrow the differential diagnosis and expedite the patient’s treatment. In an older series, Laing et al. studied the usefulness of ultrasound imaging in 52 patients with acute RUQ pain. The 52 patients were able to be accurately triaged into one of three approximately equal groups: those with acute cholecystitis (18/52), those with chronic cholecystitis (17/52), or those with nonbiliary conditions (17/52).75 In the acute cholecystitis group, there was one false-negative and five false-positive examinations yielding a sensitivity of 94% and a specificity of 85%. In the chronic cholecystitis group, the sensitivity and specificity were 71% and 97%, respectively.75
In a more recent European study, the use of ultrasound as an adjunct to initial evaluation of a general group of patients with abdominal pain was shown to increase a surgeon’s diagnostic accuracy by about 10%. It was helpful in confirming a correct diagnosis in roughly 25% of evaluations and was helpful in ruling out specific causes in roughly another 25%, being noncontributory in nearly 40% of cases.76Another randomized study published by the same authors noted that the use of surgeon-performed ultrasound allowed for significantly fewer subsequent studies, a lower “admission for observation” rate, and a higher proportion of patients submitted directly to surgery from the emergency department.77 Finally, a recent study showed a higher self-rated patient satisfaction rating on emergency department discharge in a group of patients receiving a surgeon-performed ultrasound over patients evaluated by the same surgeons without an ultrasound examination, although there was no noted change in patient mortality or other outcome.78
Evaluation of the Unstable Patient with Acute Abdominal Pain
Surgeons are often asked to evaluate a hypotensive patient with abdominal pain who is unable to provide an adequate history due to his or her existing shock state. In addition to resuscitation, the surgeon must quickly initiate an evaluation aimed at defining the cause of the abdominal catastrophe. Ultrasound imaging can be very helpful in this clinical scenario to identify the pathologic process, exclude a suspected diagnosis, or assist with percutaneous aspiration of intra-abdominal fluid. For example, aneurismal disease of the abdominal aorta has been estimated to occur in 5–10% of the geriatric population with associated hypertension or vascular disease.79 Furthermore, nearly 11,000 deaths occur annually in the United States as a result of abdominal aortic aneurysm, and almost 80% of these are from rupture.80 The diagnosis of rupture remains a challenge because the sensitivity of physical examination in stable patients ranges from 50% to 65% and its accuracy in patients with disrupted aneurysms is unknown.81 Also, these patients are generally too unstable to undergo CT scan. For detection of abdominal aortic aneurismal disease, ultrasound has been shown to have a sensitivity approaching 100% in several series.82,83 A Swiss series of 132 patients who were treated over a 5-year period found that ultrasound assisted in 22% of the diagnoses.84 Furthermore, a negative ultrasound examination of the abdominal aorta in a patient with abdominal or back pain can reliably direct a surgeon to other possible causes for the patient’s shock state.
Dehiscence and Soft Tissue Infections
Soft tissue infections may be difficult to assess by physical examination because the signs of infection may only be superficial and may not reflect the status of the entire wound. With the ultrasound transducer in hand, the surgeon can assess the presence, depth, and extent of an abscess at the patient’s bedside and determine the appropriate treatment. Furthermore, the collection can be localized to ensure its complete drainage, especially if it is loculated. In the postoperative period, wounds can be imaged to examine for hematomas or seromas. Furthermore, because the fascia can be precisely delineated with ultrasound, a fascial dehiscence (Fig. 16-15) can be diagnosed at an earlier stage.
FIGURE 16-15 Fascial dehiscence (arrow).
Foreign bodies can be the cause of recurrent soft tissue infections and, therefore, removal is often recommended. Several studies have confirmed the value of ultrasound in the detection of radiolucent foreign bodies in human tissue.85–88
The ultrasound examination of soft tissue is performed using a 5.0- to 8.0-MHz linear array transducer. The area of inflammation is scanned in both the transverse and longitudinal views to accurately assess the depth and extent of the fluid collection. The depth should be measured so that the appropriate length of the needle is chosen. Once the fluid collection is assessed, an ultrasound-guided needle aspiration may be performed. Aspiration of the collection is performed after the planned point of needle insertion is marked with a felt-tipped pen. The field is prepped and draped, and an 18-or 20-gauge needle attached to a 10- or 12-cm3 syringe is inserted into the tissue at the marked site. An alternate method involves using real-time ultrasound imaging with sterile transmission gel and a sterile plastic cover for the transducer. The ultrasound transducer is held in the nondominant hand and the area is imaged as the needle is directed into the fluid collection. The advantage of this method is that the surgeon visualizes the active drainage of the entire fluid collection and collapse of the cavity.
SURGEON-PERFORMED ULTRASOUND IN THE INTENSIVE CARE UNIT
The surgeons’ use of ultrasound is particularly applicable to the evaluation of critically ill patients in the ICU for the following reasons: (1) many patients have a depressed mental status making it difficult to elicit pertinent signs of infection; (2) physical examination is hampered by tubes, drains, and monitoring devices; (3) the clinical picture often changes necessitating frequent reassessments; (4) transportation to other areas of the hospital is not without inherent risks89; and (5) these patients frequently develop complications, which if diagnosed and treated early, may lessen their morbidity and length of stay in the ICU.90 Indeed, both diagnostic and therapeutic ultrasound examinations can be performed by the surgeon without disrupting rounds in the ICU. These focused examinations should be performed with a specific purpose and as an extension of the physical examination, not as its replacement.12
Several retrospective studies have documented the utility of portable ultrasound examinations performed in diverse groups of critically ill patients.91,92 In these studies, evaluation for sepsis of unknown origin, suspected gallbladder pathology, and renal dysfunction were the most common indications for the examinations. Slasky et al. reported their findings on the ultrasound evaluations of 107 patients in the ICU.92The sonographic results of their examinations supported the suspected diagnosis in 29 (27%) patients and excluded the initial diagnosis in 78 (73%) patients. There were no false-negative studies in this series. Additionally, 22 of the ultrasound examinations showed unsuspected abnormalities, although only 5 patients had their management altered based on these findings. In another study, however, Lichtenstein and Axler prospectively performed ultrasound examinations in 150 consecutive patients admitted to the medical ICU.91 They examined the pleural cavity, abdomen, and the femoral veins of critically ill patients and found that information derived from their sonographic examinations directly contributed to a change in the management of 33 (22%) patients. Other investigators have reported similar results and further suggest that critically ill patients most likely to benefit from a bedside ultrasound examination are those with occult hemorrhage, sepsis of unknown origin,93 and pleural effusion.12
Surgeons most commonly use bedside ultrasound examination for the evaluation of patients in the ICU to detect pleural effusions, intra-abdominal and soft tissue fluid collections, hemoperitoneum, and femoral vein thrombosis, and as a guide for the cannulation of central veins in patients with difficult access. Before introducing specific ultrasound techniques and procedures, some basic principles of interventional ultrasound will be discussed.94,95 Advantages of interventional ultrasound as used by the surgeon in the ICU include the following: (1) visualization in real-time imaging to allow direct placement of a catheter and confirmation of complete drainage of a fluid collection; (2) performance at the patient’s bedside to avoid transport; and (3) ultrasound being safe, minimally invasive, and repeatable, if necessary. Contraindications to the performance of an ultrasound-guided interventional procedure include the lack of a safe pathway, presence of a coagulopathy, and an uncooperative patient.
Larger needles and those that are Teflon coated produce more echogenicity and are easier to visualize with ultrasound.96 But, when performing a transabdominal procedure, an 18-gauge (or smaller) needle is probably preferred to avoid large injuries to the bowel. Although minor procedures may be done with minimal preparation, basic principles of sterility should be followed for major interventional procedures.
The use of ultrasound for the detection of a pleural effusion is similar to that described earlier in this chapter for the detection of a traumatic hemothorax.12 Although the technique for the focused thoracic ultrasound examination has already been described, the following is the technique used for an ultrasound-guided thoracentesis.
The head of the bed is elevated to a 45–60° angle (if the patient’s spine is not injured), or the patient may be supine if spinal precautions are needed. A 3.5- or 5.0-MHz convex array transducer is oriented for sagittal views and placed in the midaxillary line at the sixth or seventh intercostal space. The liver (or spleen) and diaphragm are identified, and then the thoracic cavity is interrogated for the presence of pleural fluid. After the fluid is localized, the area adjacent to the transducer is marked using a felt-tipped pen and the chest is prepped and draped. A local anesthetic is injected into the skin near the mark and infiltrated into the underlying subcutaneous tissue and parietal pleura. The pleural space is entered with an 18-gauge needle obtained from a central line kit, and the fluid from the pleural space is aspirated in its entirety. For large effusions, 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, if necessary, the stiff dilator is passed just through the dermis to allow easy passage of the catheter but minimize the risk of a pneumothorax. A standard central line catheter is placed into the pleural space and a three-way stopcock is connected to the port so that the pleural fluid can be aspirated entirely and collected into a separate container. The central line catheter is removed from the pleural space while applying constant suction with a syringe, and an occlusive dressing is placed over the small incision. Real-time ultrasound imaging can also be used for the detection and aspiration of small or loculated fluid collections because the needle is observed as it enters the collection and collapse of the space confirms that the fluid is entirely removed.
A sudden decrease in a patient’s blood pressure or persistent metabolic acidosis despite continued resuscitation is a common indication to reassess the peritoneal cavity as the source of hemorrhage. The FAST examination can be performed as needed at the patient’s bedside to exclude hemoperitoneum as a potential source of hypotension. This may be applied to a critically ill patient who has multisystem injuries or one receiving anticoagulation therapy. Ultrasound is also used to evaluate a patient with cirrhosis who has abdominal pain. An ultrasound-guided aspiration of ascites can also be performed, minimizing the risk of injury to the bowel.
Insertion of a Central Venous Catheter
The placement of a central venous catheter is a commonly performed procedure in critically ill patients. Although surgical residents are generally adept at the insertion of central lines, ultrasound-guided procedures may be helpful when the resident is initially learning the technique or when the patency of a vessel is uncertain. Ultrasound-guided central line insertions are especially useful in patients with anasarca or morbid obesity and for the immobilized patient with a potential injury to the cervical spine.97,98 In the past decade, several studies have evaluated the use of ultrasound as an aid for central line placement in order to reduce the risk of complications.98–104 For example, Fry et al. successfully used ultrasound-guided central venous access in 52 patients and, with the exception of a pneumothorax that occurred in 1 patient, no other complications were noted.103 These studies suggested that the use of ultrasound results in a decreased number of cannulation attempts and complications for insertion of subclavian and internal jugular venous catheters. A recent study reported similar excellent results with ultrasound-guided percutaneous access of the cephalic vein in the deltopectoral groove.104
The central veins in the cervical and upper thoracic region are imaged with a 7.5-MHz linear transducer. The skin insertion site may be marked prior to creating a sterile field, or the procedure may be performed with real-time imaging. Cannulation of the subclavian vein is slightly more difficult because of its location beneath the clavicle and, therefore, color-flow duplex and Doppler may be helpful to identify the vein prior to cannulation. Gualtieri et al.101 suggest identification of the axillary vein and artery just inferior to the lateral aspect of the clavicle. Patency of the vein is determined by its ability to be easily compressed with the ultrasound transducer. The vein is then imaged about 2–3 cm medial to the point of the planned insertion site. The transducer should be held in the nondominant hand and the cannulating needle is followed during real-time imaging as it traverses the soft tissue toward the vein. Once the vein is cannulated, the remainder of the procedure is completed using the standard Seldinger technique.
Thrombosis of the Common Femoral Vein
Despite the administration of prophylactic agents and routine screening by duplex imaging, deep venous thrombosis (DVT) still occurs in high-risk patients. The characteristics of venous thrombosis as seen on the duplex imaging study include the following: dilation, incompressibility, echogenic material within the lumen, absence or decreased spontaneous flow, and loss of phasic flow with respiration. Although each ultrasound characteristic of a thrombosed vein is important in making the diagnosis of DVT, loss of compressibility of a thrombus-filled vein is the most useful with the other criteria considered supportive of the diagnosis.105–108
A focused ultrasound examination of the femoral veins is based on the following principles: (1) most lethal pulmonary emboli originate from the iliofemoral veins;109 (2) the common femoral artery is identified as a pulsatile vessel lateral to the common femoral vein on brightness-mode (B-mode) ultrasound and provides a consistent anatomic landmark; (3) B-mode ultrasound can be used to evaluate for incompressibility of the vein, echogenic material (thrombus) within the lumen of the vein, and dilation of the vein; and (4) surgeons are familiar with B-mode ultrasound because it is frequently used to detect hemopericardium, hemoperitoneum, and pleural effusion/traumatic hemothorax in critically ill patients, hence enhancing its practical applicability in this setting.
The focused ultrasound examination of the common femoral veins is performed with the patient in the supine position as an extension of the physical examination. A 7.5-MHz linear array transducer is used to examine the common femoral veins according to the following protocol as described by Lensing et al.:105
1. The transducer is oriented for transverse imaging, and the right common femoral vein and artery are visualized (Fig. 16-16).
2. The vein is examined for the presence or absence of intraluminal echogenicity (consistent with thrombus) (Fig. 16-17) and for ease of compressibility.
3. The transducer is positioned for sagittal images, and a view of the common femoral vein is identified. The vein is inspected for intraluminal thrombus (Fig. 16-18) and adequate compressibility. The diameter of the vein is measured just distal to the saphenofemoral junction.
4. The same examination (1–3) is then conducted on the left lower extremity.
FIGURE 16-16 Transducer position for the evaluation of femoral vein.
FIGURE 16-17 Transverse ultrasound image of right common femoral vein and artery.
FIGURE 16-18 Sagittal ultrasound image of right common femoral vein with thrombus.
A positive study is defined as dilation of the common femoral vein (more than 10% increase) when compared to the same vein in the opposite extremity,110 incompressibility of the vein, and/or the presence of echogenic foci consistent with an intraluminal thrombus. A negative study is the presence of a normal-caliber vein with good compressibility and the absence of an echogenic intraluminal thrombus.
Insertion of Inferior Vena Caval Filters
Because critically ill surgical patients are at significant risk for DVT and because many have contraindications to anticoagulation, therapeutic and prophylactic inferior venal caval filters (IVCF) are being used more and more frequently. Indeed, while the topic is quite controversial, one author recommends prophylactic insertion of an IVCF within 48 hours in critically ill patients who are at high risk for DVT and have a contraindication to anticoagulation.111
While many other authors are less apt to be this aggressive, enough critically ill surgical patients require this procedure that a bedside technique for insertion would be ideal. In fact, with improvements in technology and the advent of intravascular ultrasound (IVUS), bedside insertion of IVCF is now possible.
Indeed both transabdominal duplex ultrasonography112,113 and IVUS114,115 have been used to insert vena caval filters successfully and safely at the bedside. Ashley et al.115 reported on their experience with bedside insertion of 29 IVCF using IVUS in the trauma ICU. All patients were able to have their vena caval diameter measured and renal veins located. All filters were successfully deployed in good position without complication. Follow-up CT scans in 27 of the 29 patients were available that indicated proper placement (in reference to the renal veins) in all 27 patients. A much larger experience with bedside IVCF insertion was recently published with similarly excellent results.116
After preparing the right groin and right thigh, a 9 French introducer sheath is placed in the right common femoral vein using a Seldinger technique. The stiff guidewire is passed into the right atrium. A 10-MHz IVUS catheter is aligned tip-to-tip with the filter deployment sheath. The IVUS catheter is then marked at the level of the deployment sheath hub. The IVUS images of the vena cava from the right atrium to the iliac confluence are obtained. The IVC is measured and a point 1 cm below the lowest renal vein is determined. The reference mark on the IVUS is transferred to the patient’s thigh, and the IVUS is removed. The introducer sheath is exchanged for the deployment sheath that is advanced to the correct depth and deployed. A follow-up abdominal x-ray confirms proper position of the filter.
EDUCATION OF SURGEONS IN ULTRASOUND
Although many approaches have been shown to be effective in teaching these focused ultrasound examinations, surgeons should have a solid understanding of the physics principles of ultrasound imaging as an integral part of that education process. Furthermore, these principles should be emphasized each time the examinations are taught.
The first educational model for how surgeons can learn ultrasound was published by Han et al. from Emory University.7 Incoming interns took a pretest and then attended a lecture and videotape about the FAST examination. After completion of the ATLS laboratory session, three swine had DPL catheters reinserted to infuse fluid and produce “positive” ultrasound examinations. Two other fresh swine were “negatives.” All five swine were draped similarly to disguise interventions. Incoming interns were tested individually by surgeon sonographers to determine whether the ultrasound image was “positive” or “negative.” The interns completed a posttest that showed a statistically significant improvement from the pretest . The authors concluded that incoming interns could learn the essential ultrasound principles of the FAST and that swine are feasible models for learning it. In another study using pretesting and posttesting, Ali et al. showed how a workshop in ultrasound consisting of didactics, videotapes, and hands-on demonstrations improved the ultrasound skills of nonradiologists.117
Other paradigms that have been used as educational models include cadavers whose peritoneal cavities were instilled with saline118 and simulators that had data stored in three-dimensional images.119 In the latter study, Knudson and Sisley conducted a prospective cohort study involving residents from two university trauma centers. They compared the posttest results between residents trained on a real-time ultrasound simulator and those trained in a traditional hands-on format. The main outcome measured was the residents’ performance on a standardized posttest, which included interpretation of ultrasound cases recorded on videotape. They determined no significant difference between those residents trained on the simulator and those trained on models or patients. From their study, the authors concluded that the use of a simulator is a convenient and objective method of introducing ultrasound to surgery residents.
Another issue is that of the learning curve. One of the best studies to address this issue for the FAST was conducted by Shackford et al. from the University of Vermont.11 In this study, the authors questioned the recommendations that various numbers of ultrasound examinations should be done under supervision before a surgeon is considered qualified to perform them. The authors calculated the primary and adjusted error rates and then determined the potential clinical utility of the FAST. They found that although the clinician’s (nonradiologists) initial error rate was 17%, it fell to 5% after the clinicians performed 10 examinations. Additionally, in that study, the authors proposed the following recommendations for credentialing: (1) The process for credentialing of surgeons in the use of ultrasound should occur within the Department of Surgery by either surgeons or a committee composed of surgeons and nonsurgeons that reports to the Chairperson of the Department of Surgery. (2) A formal course with 4 hours of didactic and 4 hours of “hands-on” training is adequate. The curriculum for the performance of ultrasound in trauma, recently developed by the American College of Surgeons, is strongly recommended. (3) Competency for performance of the FAST exam should be determined based on error rate with respect to the prevalence of the target disease in the series. (4) “Control” or repeat scans should be allowed during the proctored experience. (5) After completion of proctoring, an ongoing monitoring process of error rates and causes of indeterminate studies using the Department of Surgery’s quality improvement program is essential.11
The teaching of surgeon-performed ultrasound is now an integral part of the American College of Surgeons’ educational program. Modular courses begin with an ultrasound basics course, which is now available on compact disc. Advanced courses in many topics, including an “Acute/Trauma” module, are taught at the College meetings and across the country each year. A recent survey of surgeons participating in these courses shows that they have been a tremendous success.120
Experience with ultrasound is now a mandated part of residency training in general surgery. In a published survey, 95% of all residency programs are teaching ultrasonography, in either a didactic or clinic form.121 FAST, general abdominal, and breast ultrasound were all being taught in both academic and community-based programs. Academic centers additionally reported significant resident experience with IVUS, laparoscopic, and endocrine ultrasound.121Finally, a recent study documented that surgical residents could diagnose hypertrophic pyloric stenosis with 100% accuracy using ultrasound examinations.122These data suggest that ultrasound is being incorporated to a larger and larger extent in surgical training programs.
As the role of the general surgeon continues to evolve, the surgeon’s use of ultrasound will surely influence practice patterns, particularly for the evaluation of patients in the acute setting. With the use of real-time imaging, the surgeon receives “instantaneous” information to augment the physical examination, narrow the differential diagnosis, or initiate an intervention.
The advantages of ultrasound are easily seen in each of the following clinical scenarios. As a noninvasive modality, ultrasound can be used to evaluate the injured pregnant patient and simultaneously identify the fetal heart so that its rate can be recorded. For the patient with multiple fractures who is in traction, the portable machine is wheeled to the patient’s bedside and the FAST is performed without having to move the patient. If hypotension or an unexpected decrease in hematocrit occurs, an ultrasound examination can be easily repeated to exclude hemoperitoneum as the source of hypotension. When several patients with penetrating thoracoabdominal injuries present simultaneously to the emergency department, a rapid FAST examination with thoracic views can assess for pericardial effusion, massive hemothorax, or hemoperitoneum within seconds. This information helps the surgeon to prioritize resources and triage patients. Finally, ultrasound may be suitable for the initial assessment of the injured child. This painless noninvasive modality is well accepted by children because it is performed at the bedside and is not intimidating.
As surgeons become more facile with ultrasound, it is anticipated that other uses will develop to further enhance its value for the assessment of patients in the acute setting.
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