Civetta, Taylor, & Kirby's: Critical Care, 4th Edition

Section II - Monitoring

Chapter 28 - Radiographic Imaging and Bedside Ultrasound in the Intensive Care Unit

Patricia L. Abbitt

Morgan Camp

Critically ill patients often require emergent and intensive use of imaging for diagnosis and guidance for surgical and supportive maneuvers. Complex surgical or trauma patients also need follow-up imaging for successful management during postoperative or posttraumatic hospitalization. Bedside drainage procedures guided by imaging are an important part of the care of the critically ill.

Analysis of the Chest Radiograph in the Intensive Care Unit

Portable chest radiographs are the most common radiologic examination performed in patients in an intensive care unit (ICU). Chest radiographs of the ventilated patient are often used to monitor the clinical cardiopulmonary status as well as to evaluate placement of catheters and tubes. The position and any complication of placement of catheters and tubes that support the critically ill patient can be evaluated. Fluid overload, ventilator-associated pneumonia, lobar collapse, and pneumothorax are examples of parenchymal abnormalities detected and treated using the portable chest radiograph. The discussion that follows is meant to facilitate the correct interpretation of portable chest films for the intensivist.

Technical and Clinical Parameters Affecting Interpretation of the Portable Chest Radiograph

The portable AP chest radiograph taken of the critically ill patient is different from the standard upright PA and lateral chest radiograph. The portable radiograph is taken with the film relatively close to the radiographic source, which leads to enlargement of the cardiac blood vessels, and mediastinum, and can be misinterpreted as cardiomegaly, fluid overload, or a widened mediastinum. The critically ill patient is often sedated or has diminished alertness, leading to an underexpanded radiograph, which can result in small lung volumes and lower lobe volume loss or atelectasis (Fig. 28.1). Chest radiographs taken after extubation may appear “worse” when compared to films taken while the patient is receiving mechanical ventilatory support because the effects of positive pressure ventilation will be gone. Surgical procedures or disease processes affecting the upper abdomen can also contribute to elevation of the hemidiaphragms and predispose the patient to atelectasis, or even lobar collapse (Fig. 28.2). Pleural effusions develop related to fluid resuscitation with surgery or as sympathetic reactions to local inflammatory processes in the lung or upper abdomen. Pleural effusions will contribute to haziness at the lung bases and lead to nonvisualization of a diaphragm (Fig. 28.3). In the presence of a large pleural effusion, compressive atelectasis of the underlying lung will also occur.

The critically ill patient, with multiple support lines mental status and presents a challenge to the technologist filming the radiograph. Optimal positioning of the patient to include the entire lung fields and to avoid rotation of the patient on the film is quite difficult (Fig. 28.4). Cutoff of the lung apices or lung bases may occur as the technologist estimates their position. Radiographs taken in a lordotic position will accentuate the heart, making it appear larger and more globular than in standard positioning. Failure to minimize the intrusion of continuous electrocardiographic lead wires into the film will also magnify the interpretative difficulty. Interpretation of the portable chest radiograph in the intensive care unit must take into account these challenges, as well as the technical differences from the standard upright film, to provide an accurate interpretation.

Support Lines and Tubes

Multiple support lines and tubes are used to monitor and administer therapy to the ICU patient. Appropriate positioning of such support devices must be ensured devices by after placement performing a CXR to confirm placement and exclude complications such as a PRX or hematoma.

The presence of the endotracheal tube on a portable chest radiograph is indicative of ventilator support for a patient with respiratory insufficiency. The position of the endotracheal tube (ET) in most cases is determined by locating the radiopaque marker on the wall of the tube. The ET tube is ideally located in the trachea 2 to 4 cm above the carina or projected between the head of the clavicles and above the carina (Fig. 28.5). An ET that has been advanced too far into the airway may enter one of the two main bronchi, which can cause lobar collapse since the contralateral bronchial orifice would be blocked by the ET. Intubation of the right lower lobe bronchus can happen easily in an emergent or field intubation because the trajectory of the right lower lobe bronchus is quite straight from the trachea (Fig. 28.6). Intubation of the right lower lobe bronchus may result in obstruction of the left bronchus, resulting in left lung collapse (Fig. 28.7) or right upper lobe bronchial obstruction with right upper lobe collapse. The inappropriate position of the ET leads to problems with patient ventilation until the endotracheal tube position is corrected.

Figure 28.1. These two radiographs demonstrate the marked difference in the appearance of the chest when the film is taken (A) portably or (B) in the upright position. In the underexpanded portable chest film (A), the mediastinum looks wide, the heart looks bigger, and the vessels often look plumper. The diagnosis of fluid overload is erroneous as demonstrated by a radiograph taken minutes later (B) in the upright full inspiratory mode.

Figure 28.2. Lower lobe densities in this case are related to lobar collapse at the bases. The hemidiaphragms are elevated, and the heart is obscured by the densities caused by lower lobe collapse/volume loss. Lower lobe collapse can be differentiated from pleural effusions in this case because effusions would layer, causing haziness in the recumbent, critically ill patient.

Central Catheter Placement

Central venous catheters to be used for fluid, antibiotic administration, or parenteral nutrition may be placed into the subclavian or jugular veins with their tips projecting into the superior vena cava (SVC). The junction of the subclavian vein and jugular vein is usually located behind the medial head of the clavicle, so the course of the catheter in relation to the vessel should be evaluated. Most central catheters which are used for central venous access are designed to terminate in the SVC, between the level of the clavicles and the carina, keeping the venous catheter above the reflection of the pericardium at the base of the great vessels (Fig. 28.8). This ensures that, if the superior vena cava is perforated by the catheter tip, bleeding into the pericardium will not occur. Therefore catheters that are advanced too far into the right heart or even into the inferior vena cava should be retracted, leaving the tip in the SVC. Some central venous access catheters, notably dialysis catheters, are designed to terminate in the right heart (Fig. 28.9).

Figure 28.3. There is a sizable left pleural effusion that causes a gradient of density in the left chest and obscures the left hemidiaphragm, as opposed to the lucent right lung and clear diaphragm.

Figure 28.4. The mediastinum (arrows) is rotated to the right in this case, illustrating the difficulty of correctly positioning the critically ill patient on the film.

Figure 28.5. The endotracheal tube (arrows) is located in the trachea, between the clavicles and above the carina. The radiopaque marker is on one side of the tube to help identify its tip. Its position above the carina ensures equal ventilation to both lungs.

Figure 28.6. The small-bore tube changer used in this patient with cervical spinal traction has cannulated the right bronchus (arrow) reflecting its straight trajectory from the trachea. The tube changer can be used to maintain access to the airway in patients in whom reintubation may be necessary.

When central venous catheters are placed into the chest, especially subclavian catheters, a postprocedural chest radiograph should be obtained to check catheter placement and to check for postprocedural complications, such as a pneumothorax. The apex of the lung is in close proximity to the puncture site for a subclavian catheter and thus, is at risk for a pneumothorax. The proceduralist may expect to see a pneumothorax on the postprocedure chest film if the patient suddenly became short of breath, complained of chest pain, or if there was desaturation of oxygenation with catheter placement. A pneumothorax can also be asymptomatic.

Figure 28.7. Emergent intubation has resulted in intubation of the bronchus intermedius. The left bronchus is blocked by the endotracheal tube. The entire left lung is collapsed, leading to an airless white left chest with shift of the mediastinum and heart to the left.

Figure 28.8. The tip of the central catheter (arrows) is in good position in the superior vena cava.

A pneumothorax is recognized by visualization of the pleural interface inside the thoracic cavity where there is also an absence of lung markings, penpherally. Increased lucency (air) will surround the lung because of the extra air (Fig. 28.10). (Fig. 28.11). Tension pneumothorax may cause downward displacement on the diaphragm or contralateral mediastinal shift as the air accumulates within the pleural space (Fig. 28.12). The development of a tension pneumothorax may be correlated with sudden decompensation and require urgent intervention. A small pneumothorax in a patient on a ventilator may suddenly convert to a tension pneumothorax secondary to the presence of positive pressure ventilation. For this reason, patients on positive pressure ventilation who develop a pneumothorax will often be treated with a chest tube to avoid the development of a tension pneumothorax. Pneumothoraces are not only the result of central catheter placement but can be secondary to barotrauma with increasing ventilatory settings or secondary to chest trauma and rib fractures (Fig. 28.13).

Figure 28.9. The tip of the larger-bore dialysis catheter is in the right atrium (double arrows), a deeper position than is expected for most standard central catheters. The introducer, a central catheter (bold arrow), is in good position in the SVC.

Figure 28.10. The lung edge (arrows) is noted at the right apex on this patient after a central catheter placement attempt. A chest tube was not immediately placed since the patient was stable and the pneumothorax was small.

Figure 28.11. A large pneumothorax is present on the right. Air fills the right chest. There are no lung markings and the entire right lung has fallen centrally (arrow). The attempt at catheter placement was unsuccessful. No central venous catheter is noted. There is also a deep sulcus sign overlying the right diaphragm.

Figure 28.12. A: After catheter placement, a follow-up chest radiograph shows a large pneumothorax on the left. The lung edge is indicated by arrows. There is a shift of the mediastinum and depression of the left hemidiaphragm indicating a tension component. B: A chest tube (arrow) was inserted quickly to relieve the pneumothorax.

Figure 28.13. A tension pneumothorax is obvious, causing shift of the mediastinum toward the right. The left hemidiaphragm is depressed. Multiple left rib fractures are the cause of the tension pneumothorax in this case. Emergent left chest tube placement is necessary.

Figure 28.14. A skinfold (arrows) may be misinterpreted as a pleural catheter and lead to unnecessary chest tube placement. Recognizing the difference in appearance from the pleural edge and recognizing vascular markings peripheral to the skinfold will prevent an error from being made.

Figure 28.15. The presence of a large left pneumothorax may be hard to visualize in the recumbent patient. Vascular markings are lacking at the left apex, and there is increased lucency on the left indicating the presence of air in the left pleural space.

The pleural interface that indicates the presence of a pneumothorax is not to be confused with a skinfold (Fig. 28.14). Skinfolds may be seen in older patients with redundant skin and can be misinterpreted as a pleural edge, or leading to misdiagnosis of a pneumothorax and inadvertant chest tube placement.

Figure 28.16. The tip of the pulmonary artery catheter (arrows) is well out of the left pulmonary artery. The catheter needs to be withdrawn several centimeters to be in optimal position with the tip of the catheter closer to the mediastinum.

Figure 28.17. The left upper extremity PICC (arrow) extends into the left neck from the left arm and needs to be repositioned.

The critically ill patient is most often in the recumbent position after central catheter placement, which can make the recognition of a pneumothorax difficult (Fig. 28.15). A pneumothorax in the recumbent position may collect anteriorly, at the lung base, leading to the deep sulcus sign. The deep sulcus sign is the lucency at the lung base caused by air trapped in the most anterior portion of the pleural space in a recumbent patient. This sign is a critical, yet subtle, finding that makes tremendous difference in a patients status. In critically ill patients who are difficult to position, the base of the lung may not be imaged, eliminating this diagnostic area on the film.

Figure 28.18. The tip of a weighted feeding tube is in the stomach (arrow).

Figure 28.19. The feeding tube follows the gentle curvature of the stomach (arrow), descends in the duodenum (double arrow), and crosses back over the midline with the weighted tip at the level of the ligament of Treitz and in excellent position for feeding.

Figure 28.20. The tip of the feeding tube is in excellent position for feeding (arrow).

Figure 28.21. Contrast has been injected into the feeding tube to demonstrate that its tip is in the proximal jejunum and in excellent position for feeding. The small bowel folds are feathery in appearance (arrow). Contrast confirms that the tube is not coiled in the stomach.

A pulmonary artery catheter (PAC) is usually placed via an introducer into the subclavian or jugular vein and advanced into either the right (most commonly) or left pulmonary artery to facilitate its use as a monitor of cardiac function. The pulmonary artery catheter ideally should be positioned in the proximal right or left pulmonary artery. If the catheter is advanced too far distally, the balloon tip can cause pulmonary infarction (Fig. 28.16). If the pulmonary artery catheter is placed to be too proximal, as in the right ventricle, the catheter could trigger dysrhythmias and promote inaccurate measurements.

Figure 28.22. The feeding tube is not seen below the diaphragm. Its tip is seen above the diaphragm in the left lower lobe bronchus (arrow). If the tube's malposition is recognized and the tube is removed prior to feeding, no problems should ensue.

Figure 28.23. A: Tip of the weighted feeding tube (arrow) is in the bronchus to the right lower lobe, indicating the patient's inability to protect his airway. There is a nasogastric (NG) tube, indicated by the radiopaque stripe, coiled in the stomach (double arrows). B: Chest radiograph of the same patient showing the feeding tube in the right bronchus (arrow) and the NG tube in the esophagus (double arrows).

Figure 28.24. A: The feeding tube is coiled in the right lower lobe bronchus (arrow). B: After removal of the feeding tube, a tension pneumothorax became obvious on the right. The air, which is lucent in the pleural space, causes mass effect on the dense, noncompliant, wet right lung, which is unable to completely collapse. Prompt chest tube placement was necessary.

A peripherally inserted central catheter (PICC) is a long intravenous catheter, usually advanced from a peripheral upper extremity vein with optimal positioning of its tip in the SVC.

A puncture of the lung and subsequent pneumothorax is not expected with PICC placement. The PICC is often hard to visualize on a radiograph since it is so small. Contrast instillation at the time of the radiograph may help in localizing the tip of a PICC. Peripherally inserted central catheters may be advanced too far into the heart, may coil in a vessel, or extend into the jugular vein from the subclavian vein (Fig. 28.17). In any of these situations, manipulation of the catheter will be necessary to optimize its placement. Some peripherally inserted central catheters cannot tolerate rapid injections of contrast agents necessary for CT scanning. The capabilities of the catheter for contrast injections are usually available from the product manufacturers on the product inserts.

Figure 28.25. A: The feeding tube had been aggressively advanced into the left bronchus and was coiled in the left pleural space. B: Removal of the feeding tube led to the rapid development of a tension pneumothorax on the left, necessitating chest tube placement. Notice the lack of lung markings associated with the left pneumothorax.

The subclavian artery and vein course together, and plain radiographs of a PICC may not allow a distinction to be made of whether the catheter is in the vein or the artery. Clinical evaluation of catheter placement, either by transducing for a pressure reading or determining the oxygen saturation value of the blood, may be useful if there is concern that the catheter has been placed into the artery.

Feeding Tube Placement

A nasally or orally placed feeding tube is a commonly utilized in the critically ill patient. Feeding tube placement is considered optimal when the tip of the feeding tube is in the distal duodenum or proximal jejunum so that the risk of reflux of the administered feeds into the stomach will be minimized. Many of the commonly used enteral tubes have a weighted metallic tip to facilitate peristaltic movement into the small bowel. This weighted tip facilitates the recognition of the tube on the abdominal radiograph (Fig. 28.18). Some feeding tubes are placed surgically, and their appearance may be different (e.g. larger bore). Nasogastric (NG) tubes are meant to reside within the stomach for gastric decompression, administration of oral medications, and gastric pH monitoring. Most NG tubes have a radiopaque stripe marking the length of the tube with a side hole obvious as a break in the marker. The most proximal sidehole of the NG tube needs to reside in the stomach.

The ideal position for a feeding tube placed orally is with its tip at the ligament of Treitz or at least in the distal duodenum so reflux into the stomach and esophagus with feedings will not occur (Figs. 28.19, 28.20 and 28.21). In patients with neurological injuries, or in heavily medicated patients, the inability to protect their airway may lead to cannulation of the bronchus with the feeding tube (Fig. 28.22). Similar to ETT placement, the right lower lobe bronchus may be cannulated by the enteric tube because of its relatively straight course from the mouth (Fig. 28.23). Feeding tube malposition must be recognized to avoid the disastrous consequences of administering feeds into the lung.

Figure 28.26. There is a triangular density at the right lung base (arrows) and shift of the heart toward the right, findings of right lower lobe collapse secondary to a mucus plug in the bronchus.

Figure 28.27. A: Preoperative chest radiograph shows excellent visualization of both hemidiaphragms and clear lungs. B: Postoperative (status post–median sternotomy) chest radiograph shows increased retrocardiac density, inability to see the left hemidiaphragm, inability to see through the heart, and shift of the heart toward the left—all findings of left lower lobe collapse.

A feeding tube that has been inadvertently placed into the bronchus and then advanced into the lung parenchyma may cause a sudden tension pneumothorax when the tube is removed from the lung because when such a tube is removed, the hole in the pleura and lung may result in a large gush of air and the development of a tension pneumothorax. (Figs. 28.24 and 28.25).

Figure 28.28. The triangular density in the right lung apex is right upper lobe collapse secondary to the low position of the endotracheal tube (ET) with obstruction of the right upper lobe bronchus. Retraction of the ET may allow re-expansion of the right upper lobe.

Parenchymal Abnormalities Seen on Chest Radiograph in the ICU

Collapsed Lung

Areas of collapsed lung are frequently seen on chest radiographs of the critically ill patient. Collapsed lung will be dense (white) on the chest film and will take up less room than a fully expanded, normally aerated lung (Fig. 28.26).

The most frequently encountered lobar collapse in the intensive care unit is left lower lobe collapse. Ventilator-dependent recumbent patients develop collapse in the left lower lobe, usually secondary to diminished inspiratory effort, recumbent positioning, and the weight of the heart on the left lower lobe. On the chest film, left lower lobe collapse will result in increased density in the retrocardiac area. This is recognized by an inability to “see through” the heart to visualize the lower lobe pulmonary artery, and the left hemidiaphragm. The inability to visualize the hemidiaphragm on the left is secondary to the fact that the left lower lobe is airless. It is the air in the lower lobes that allows the diaphragm to be seen as a linear structure. In the patient with left lower lobe collapse, the heart and mediastinum with shift toward the left, since the collapsed left lower lobe is taking up less room than a normally expanded, fully aerated lobe (Fig. 28.27).

Figure 28.29. After pulmonary artery catheter placement, the triangular density of right upper lobe collapse (arrows) was noted.

Figure 28.30. A: Normal preoperative radiograph. B: The triangular density of right upper lobe collapse is noted in this patient after fixation of the cervical spine.

A malpositioned ET tube can lead to lobar or lung collapse by occluding the airway and preventing ventilation (Fig. 28.28). Repositioning of the ET tube may lead to complete re-expansion of the lung in some cases. Often, bronchoscopy is necessary to optimize ventilation by removing a mucous plug to improve ventilation.

Figure 28.31. A: Right upper lobe collapse. B: Resolution after aggressive chest PT was administered.

Right upper lobe collapse causes a characteristic triangular density in the right lung apex. This characteristic triangular density should be recognized, as it might be encountered after intubation. Its appearance is characteristic and is not to be confused with a localized hemothorax, loculatal, pleural effusion, pneumothorax or pneumonia. The smooth inferior margin of the density is the minor fissure that sharply marginates the density and is pulled superiorly by the volume loss in the right upper lobe (Figs. 28.29 and 28.30). Right upper lobe collapse may respond to ET tube manipulation, bronchoscopy, or chest PT. Re-expansion of the right upper lobe can be documented by chest radiograph after such maneuvers (Fig. 28.31).

“White Out” of the Chest

A critically ill patient may present with clinical decompensation and a “white out” of one lung on the chest film. Careful analysis of the film is necessary to draw the correct conclusions, which will determine therapy.

Figure 28.32. There is complete opacification of the right chest, and the heart is pushed away from the right chest, suggesting that there is something (fluid or mass) filling the right chest and having mass effect. CT scanning subsequently showed a large mass and effusion filling the right chest. There was associated compressive atelectasis or collapse of the right lung.

A completely opacified hemithorax may be secondary to a large pleural effusion that fills the chest. The underlying lung may be compressed and surrounded by the large amount of fluid. When a large pleural effusion fills one hemithorax and the underlying lung is collapsed, the heart and mediastinum will be shifted away from the side filled with fluid (Fig. 28.32).

In some situations, the entire lung collapses secondary to mucus plugging or airway obstruction. In these circumstances in which there is no significant volume of pleural fluid, the mediastinum and heart will shift toward the side of collapse, which is also the side of airway obstruction (Fig. 28.33). This distinction of shift of the heart and mediastinum toward atelectatic lung, or away from a large effusion is critical because the observation leads to dramatically different therapies (bronchoscopy or chest tube) which immediately improve a patients ventilation (Fig. 28.34).

Pleural Effusions in the Intensive Care Unit

Pleural effusions that are large but do not completely fill the chest will, cause a gradient of haziness that obscures the hemidiaphragm and is worse at the lung base which gradually fades toward the lung apex. Pleural effusions in the recumbent patient do not cause a meniscus as they do in an upright patient because the effusion layers posteriorly in the supine patient. A large unilateral pleural effusion may cause an asymmetric density in the affected chest, and the presence of the effusion will be suggested by the difference in density in the two hemithoraces.

Lateral decubitus chest radiographs or bedside chest ultrasound may verify the presence of pleural effusion suspected on plain chest radiographs. Furthermore ultrasound of the chest, show the compressed underlying lung, and allow quantification of the pleural fluid (Fig. 28.35). Loculated fluid or internal septations within the fluid suggest that the pleural fluid is infected or hemorrhagic. Pleural fluid that is infected—that is, an empyema—needs drainage. Acute hematoma or an empyema may be difficult to drain with thoracentesis or small-bore chest tubes, requiring either large-bore chest tubes or surgical decompression. Sometimes moderate to large effusions which cause the lung to collapse, can be drained to improve a patients ventilatory status to keep them from being intubated or to facilitate extubation (Fig. 28.36).

Figure 28.33. There is complete opacification of the left chest, and the heart is hidden in the density consistent with a completely collapsed left lung secondary to airway occlusion related to a mucus plug. No significant effusion is present, indicated by the fact that the heart is hidden in the density of the left chest rather than being shifted to the right. Bronchoscopy was necessary to remove the plug and allow re-expansion of the left lung.

Figure 28.34. Complete opacification of the left chest in this trauma patient is secondary to left lung collapse related to the inappropriate endotracheal tube (ET) position. Retraction of the ET should aid left lung re-expansion.

Figure 28.35. A and B: Ultrasound shows a large effusion (blank space) outlining the hemidiaphragm (arrows).

Airspace or Alveolar Opacification

Aspiration or ventilator-associated pneumonia (VAP) are two respiratory events that may complicate the clinical course of the patient in the ICU. Aspiration or VAP may prolong the stay in the ICU by contributing to respiratory failure and sepsis.

Figure 28.36. A: A large right pleural effusion causes diffuse opacification on the right. B: Placement of a pleural drain allowed normal aeration of the right lung. The pigtail pleural drainage catheter is indicated by the arrow. Note the resolution of the haziness and opacification of the right chest. The right hemidiaphragm is now visible.

On a chest radiograph, VAP appreciated by an area of airspace opacification (cloud like) in the lung (Fig. 28.37). The region of VAP may begin in an area of lobar or segmental collapse. Air bronchograms may be seen, which are air-filled bronchi surrounded by infectious material in the alveoli of the lungs. Visualization of air bronchograms allows recognition that the process is a parenchymal or lung process, not a pleural effusion (Fig. 28.38). Patchy cloudlike opacification on the chest film is also indicative that the process is parenchymal.

The sudden onset of a large parenchymal consolidation, particularly in the lower lobes especially in the correct clinical scenario, may indicate that large volume bilaterally aspiration has occurred. Sometimes this can be confirmed at bronchoscopy when food particles are retrieved, substantiating the impression of aspiration (Figs. 28.39, 28.40, 28.41).

Figure 28.37. A: Tracheostomy tube noted in good position with clear lungs. B: Subsequently a large area of new left lung airspace opacification was noted on chest radiograph demonstrating interval development of ventilator-associated pneumonia (VAP).

Fluid Overload Pattern

Massive fluid resuscitation is sometimes necessary in patients with trauma, during surgery, or as part of the management for sepsis. A fluid overload pattern may become obvious on a chest film with bilateral perihylar airspace opacification and bilateral pleural effusions. Patients with cardiogenic pulmonary edema and heart failure may have similar findings on a chest radiograph. Diffuse bilateral parenchymal opacification could also be seen in extensive pneumonia, pulmonary hemorrhage, or ARDS (acute respiratory distress syndrome). Cardiovascular monitoring, the clinical scenario and bronchoscopic results may be helpful in differentiating the various causes of the parenchymal opacification (Figs. 28.42, 28.43, 28.44).

Figure 28.38. Aspiration pneumonia was documented on CT as a unilateral parenchymal process in the right lung. Air bronchograms are obvious (arrow).

Cross-Sectional Imaging in the Critically Ill Patient

There are numerous medical or surgical situations that may result in an admission to the ICU. Cross-sectional imaging, often with CT, is instrumental in allowing rapid recognition of the correct diagnosis to facilitate care and follow-up in the critically ill patient.

CT scanning is the workhorse of diagnosis and imaging of the critically ill patient. Intravenous and oral contrast agents are used to optimize imaging, but their use may raise certain concerns. Intravenous contrast administration is especially helpful in vascular diagnoses such as aortic dissection or acute mesenteric thrombosis allowing recognition of an intimal flap in the aorta or embolus in mesenteric vessels. Intravenous contrast can be nephrotoxic in patients with renal insufficiency therefore. Pretreatment of such patients with fluid optimization, N-acetyl cysteine, and alkalinization¹ may minimize the effects of intravenous iodinated contrast agents. In some cases, intravenous contrast is not necessary for the particular question asked (e.g., “Is there free air?”) and can be avoided. To administer intravenous contrast at a rapid rate for the scan, a well-placed venous access catheter is necessary.

Oral contrast is beneficial in many situations by delineating the GI tract from an abcess or mass and also to confirm a leak. However oral contrast should not be used in most emergent situations because it can delay a critical scan, or a patient cannot tolerate the volume of fluids. Also, iodine-based oral contrast agents are quite toxic to the lungs, so every effort should be made to avoid aspiration. Patients at aspiration risk should be monitored as the oral contrast is administered and while the contrast is in the stomach. Administration of oral contrast into enteral tubes that are located beyond the stomach can be helpful.

Figure 28.39. A–C: This young woman was witnessed to aspirate during an emergent delivery of a premature infant. CT images demonstrate the focal, unilateral airspace disease on the left.

Cross-Sectional Imaging in Certain Critical Situations

Aortic Aneurysm Rupture

Aortic aneurysm rupture is often seen in an older patient with atherosclerotic disease, which may present by severe back pain, hypotension, and cardiovascular collapse.

If the diagnosis is suspected, the most rapid recognition of an aortic aneurysm can be made by bedside ultrasound. Recognition of retroperitoneal hemorrhage accompanying aortic rupture may be limited with bedside ultrasound. CT allows visualization of the aortic aneurysm, with fluid and stranding in the retroperitoneum related to aortic leaking (Fig. 28.45). Immediate repair may be attempted by either open surgery or endoluminal stent placement. Emergent and massive resuscitation is often necessary in patients with aortic rupture.

Aortic Dissection

Aortic dissection typically causes severe back pain and can be confused clinically with myocardial infarction or pancreatitis (Fig. 28.46). Contrast enhanced CT or MR can be used in the emergent setting to make the diagnosis of aortic dissection as well as to define the extent of the dissection. Involvement of the aortic root or ascending aorta by a dissection is usually treated surgically to avoid or minimize complications of cardiac tamponade, myocardial infarction, or aortic valvular insufficiency. Aortic dissection that begins distal to the takeoff of the left subclavian artery may be treated medically with antihypertensive medications unless there are complicating factors such as mesenteric ischemia or renal dysfunction from aortic dissection. Endoluminal stents are increasingly being used in situations of aortic dissection.

Figure 28.40. A trauma patient requiring prolonged extrication had extensive bilateral parenchymal opacification related to aspiration.

Figure 28.41. The postoperative radiograph shows the interval development of bibasilar airspace opacification, worse on the right. Clinically obvious aspiration occurred postoperatively.

Aortic Injury

Acute aortic injury occurs with significant chest trauma, particularly acute decelaration injuries, and is most often located near the embryonic attachment of the aorta to the pulmonary artery. Luminal irregularities at this site with surrounding mediastinal hematoma indicate a potentially unstable vascular injury. Either open surgical management or endoluminal stent grafting can be used for repair. Active arterial extravasation of contrast at the site of aortic injury does not have to be present to have an unstable aortic injury (Fig. 28.47).

Severe Pancreatitis

Pancreatitis has many causes, including alcohol abuse, gallstone passage, hypertriglyceridemia, and trauma. Acute pancreatitis from any cause can result in severe pain, nausea, and vomiting. Fluid resuscitation and electrolyte management are imperative in the affected patient and may necessitate an admission to the ICU. Peripancreatic fluid collections, which can become infected, often develop after a bout of severe pancreatitis. The severity of pancreatitis and complicating features like pseudoaneurysm formation, or splenic vein thrombosis can be elucidated by cross-sectional imaging (Fig. 28.48).

Trauma

Ultrasound of the trauma patient in the emergency department can detect free fluid, likely blood, related to organ injury. Subsequent CT scanning allows rapid evaluation of trauma to the head, chest, abdomen, and pelvis and any complicated extremity injuries. Three-phase imaging allows recognition of arterial bleeding, organ contusion or laceration, and urinary system injury. State-of-the-art scanners are rapid and can guide emergent surgical management or direct critical care monitoring.

Figure 28.42. Preoperative (A) and postoperative (B) radiographs show the interval development of diffuse bilateral airspace opacification, consistent with pulmonary edema related to massive fluid resuscitation.

In the acute setting, arterial bleeding from organs or soft tissues must be managed immediately to prevent patient death. Blunt trauma can cause life-threatening hepatic, splenic, renal, or aortic trauma. Penetrating trauma likewise can result in arterial injury. Rapid surgery to stop bleeding or angiographic embolization are the two most common ways arterial bleeding is managed (Fig. 28.49). Critical neurological injuries that need emergent treatment are also evaluated during a trauma CT.

Figure 28.43. Pulmonary edema pattern with bilateral airspace opacification.

Figure 28.44. Chest radiograph and CT images of a patient with heart failure/fluid overload. Note the patchy bilateral parenchymal involvement.

Figure 28.45. CT scan with intravenous contrast shows a large infrarenal aortic aneurysm and stranding (arrows) into the left retroperitoneum, indicating leakage around the aorta. This patient underwent emergent open repair.

Figure 28.46. Aortic dissection is present in this case involving the ascending and descending thoracic aorta. The intimal flap separating the true and false lumen of the dissection is marked by arrows. Replacement of the aortic root and valve to minimize aortic insufficiency and cardiac tamponade was necessary.

Figure 28.47. A–C: Acute aortic injury is identified here by recognition of the abnormal contour of the aorta (arrows) and the surrounding mediastinal hematoma. This is the typical site of aortic deceleration injury.

Figure 28.48. An acutely swollen edematous pancreas with peripancreatic stranding (arrows) is demonstrated in this case. Fluid resuscitation and electrolyte management were important features of this patient's care.

Figure 28.49. A–C: This 19-year-old man has a large liver laceration with active arterial extravasation. Contrast-laden blood is demonstrated squirting from the liver (arrow). Emergent surgery was necessary for control of the bleeding.

Postoperative Bleeding

Life-threatening hemorrhage may occur in an operative bed and result in rapid exsanguination. Immediate diagnostic imaging capabilities are essential in such cases to allow the diagnosis to be made and rapid repair efforts to occur (Fig. 28.50). Postoperative hemorrhage may be repaired by emergent surgery or embolization.

Sepsis/Septic Shock

Sepsis frequently occurs in ICU patients especially in the postoperative patient. CT scanning can identify sites of unsuspected abscess formation. Recognition and drainage of abscesses or fluid collections in the unstable septic patient can help treat the infection and improve a patients status (Fig. 28.51). Drainage procedures of the abscesses may be performed using percutaneous image-guided procedures or surgery. Some drainage procedures may be performed at the bedside on unstable patients using ultrasound. Other image-guided procedures require CT or fluoroscopy. Follow-up imaging after drainage will provide information regarding the efficacy of the drainage procedure.

Figure 28.50. A and B: A large hematoma and active arterial extravasation (arrows) were obvious in this patient after radical nephrectomy for renal cell carcinoma. Arterial embolization was successful in halting the bleeding and stabilizing the patient.

Mesenteric Ischemia/Infarction

Patients with mesenteric ischemia may complain of severe abdominal pain, out of proportion to the clinical examination. Patients with mesenteric compromise may have elevated lactic acid levels and elevated white blood cell counts. One often finds, in these cases, pre-existing risk factors such as severe atherosclerotic disease, emboli events secondary to atrial fibrillation, or profound episodes of global hypotension. Venous thrombosis is a less frequently encountered cause of mesenteric ischemia. Sometimes, vascular occlusion or an embolus can be seen in an artery of the gastrointestinal (GI) tract on contrast-enhanced CT. CT scanning may show pneumatosis intestinalis (air in the bowel wall), portal venous gas, or free air, all possible manifestations of bowel necrosis and infarction (Fig. 28.52). Patients with acute mesenteric ischemia do not necessarily show CT signs of bowel compromise and may benefit from surgical exploration to exclude mesenteric ischemia if the CT scan is unrevealing in the appropriate clinical setting. Pneumatosis intestinalis may be an innocuous finding, so correlation with the clinical situation should be made before the patient is taken to surgery.

Figure 28.51. A–C: Multiple low-density liver lesions were identified (arrows) and eventually drained in this patient who presented with sepsis and hypotension related to cholangitis and liver abscesses.

Figure 28.52. A–C: Multiple loops of small bowel are noted here to have air in the wall consistent with pneumatosis intestinalis (arrows). The patient's clinical status with septic parameters, hypotension, and elevated lactic acid levels made bowel ischemia likely. Necrotic bowel was resected at laparotomy.

Pulmonary Emboli

Significant emboli to the pulmonary arteries usually come from the legs or pelvis and may cause rapid patient decompensation. Many patients are at risk for the development of pulmonary emboli, especially after trauma, prolonged surgical procedures, and the hypercoagulability of malignancy. CT scanning of the chest with rapid infusion of intravenous contrast will allow the diagnosis and extent of pulmonary emboli to be evaluated so that appropriate therapy can be initiated (Figs. 28.53 and 28.54). Anticoagulation with heparin, low-molecular-weight heparinoids, and long-term Coumadin use are the most common ways pulmonary emboli are treated; otherwise inferior vena caval filters may be necessary. In rare cases, where large, central or saddle emboli are present which are causing right heart strain the use of thrombolytic agents and thrombus extraction may be tried.

Figure 28.53. Multiple large filling defects (arrows) in the pulmonary arteries are present, consistent with pulmonary emboli. The patient's chest radiograph at this time was normal and clear.

Figure 28.54. A–C: Another patient with massive pulmonary emboli (arrows).

Image-Guided Interventional Procedures at the Bedside

Image-guided procedures play a critical role in the care of patients in the ICU. Fluoroscopic or ultrasound decompression of the biliary tree or of an obstructed kidney may be necessary to manage a septic, obstructed patient. Some procedures will require that the patients be moved to the operative or fluoroscopic suite so that the procedure can be performed.

Bedside procedures to drain abscesses, fluid collections or chest tube placement can often be performed without moving the patient from the ICU. By keeping the patient in his or her bed, the critically ill patient remains surrounded by those who know him medically the best—his nurses, respiratory therapists, and physicians. Any decompensation or change in patient status during the performance of the procedure can be dealt with by individuals familiar with the patient's care. Multiple transfers of the patient from bed to bed are eliminated if the patient remains in the unit. Dislodging important monitoring or support lines such as the endotracheal tube is less likely to occur if fewer transfers of the patient are made.

Figure 28.55. A: A large peripherally enhancing loculated collection was detected by CT but drained by ultrasound (B and C) in this unstable liver transplant recipient. Multiple septations and internal debris were present on ultrasound. Gram-negative rods were identified on Gram strain.

Figure 28.56. A: This postoperative patient became septic with positive blood cultures and elevation of white blood cell count. CT scanning showed a massively distended and sludge-filled gallbladder. Clinically, the gallbladder was palpable and tender. B: Postdrainage, the gallbladder is decompressed by a tube that goes through the liver. The material in the gallbladder was frankly purulent and grew Staphylococcus aureus.

Bedside procedures on the critically ill patient are usually guided by ultrasound since it is a portable imaging modality. Ultrasound is ideal for localizing and draining large pleural effusions, large superficial fluid collections or abscesses, ascites, and gallbladder decompressions (Fig. 28.55). Air obscures the imaging efficacy of ultrasound, so pneumothorax, free air in the abdomen, or ileus with air-distended bowel makes ultrasound visualization limited. Some catheter placements deep in the pelvis or in posterior sites will require CT localization and will require the patient to be transported to the CT suite.

Figure 28.57. A distended gallbladder is visualized on bedside ultrasound (A and B). After the bedside drainage procedure (C and D), the gallbladder is decompressed and the drainage catheter is obvious within the lumen of the gallbladder (arrow). A small amount of liver has been traversed to place the drainage catheter.

Ultrasound-guided procedures require that the patient be positioned to optimize visualization of the collection to be drained. The collection can be drained after it has been determined that the patient's coagulation factors are satisfactory (usually INR [international normalized ratio] of 1.5 or less and platelet count of 50,000 cells/microL or greater) and informed consent is obtained. Collections are drained using the Seldinger technique. The collection is entered with a hollow needle, avoiding nearby vessels or organs. A guidewire is advanced into the collection. Several dilations are made over the guidewire, and a catheter is placed into the collection. Decompression of the collection is performed by manual withdrawal of the material. Jackson-Pratt suctioning is generally attached to the catheter for long-term suction. The material from the collection can be sent for analysis, including Gram strain, culture and sensitivity, and chemistries such as amylase, lipase, and pH. Postprocedure imaging and clinical follow-up of the output of the drainage catheter will assess the efficacy of the drainage procedure.

Figure 28.58. A: Large bilateral pleural effusions were successfully decompressed by placement of pleural drainage catheters. B: Note the resolution of the pleural densities with drainage. Catheter drainage helped ease the patient's respiratory distress.

Figure 28.59. CT scanning showed a large pleural effusion with enhancement of the pleura consistent with an empyema, in a patient with fever and markedly elevated white blood cell count. Bedside drainage was performed and with the use of TPA and the percutaneous drainage catheter, 1,800 mL of serosanguineous fluid was withdrawn. Postprocedure chest radiograph showed remarkable clearing of the right chest. The infected fluid had a pH of less than 6.8. The patient's white blood cell count improved significantly after chest drainage.

Gallbladder decompression is generally performed on extremely ill, unstable, and septic patients with obstruction of their gallbladder either related to gallstones or acalculous cholecystitis. Gallbladder drainage is generally reserved for patients too unstable to undergo surgical removal of an obstructed and infected gallbladder who are thought to be septic with the gallbladder considered to be the source. Placement of gallbladder decompressive tubes should be through the liver into the gallbladder. The tube should be left in place for 6 to 8 weeks to minimize the chance of a bile leakage from the gallbladder. Possible complications of gallbladder drainage procedures include bile peritonitis, hemorrhage, or liver injury (Figs. 28.56 and 28.57).

Drainage of large pleural effusions may lessen the need for ventilatory support, allow the underlying lung to re-expand, and disclose underlying parenchymal disease (Figs. 28.58 and 28.59). Empyemas or infected pleural collections can be managed by image-guided tube placement to ensure complete drainage.

The critically ill patient in the ICU requires extensive and recurrent use of imaging to optimally diagnose and manage care. Diagnosis with portable chest radiographs or CT scans allow recognition of life-threatening conditions that require intervention. Bedside procedures usually with ultrasound guidance can not only be diagnostic but therapeutic as well.

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