Bongard Frederic , Darryl Sue. Diagnosis and Treatment Critical Care

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007

Imaging Procedures

Kathleen Brown, MD

Steven S. Raman, MD

Nam C. Yu, MD

An unprecedented array of imaging options is now avail-

able to the physician in the ICU. The choice of a particular

imaging modality is occasionally difficult and should be

based on recommendations in the literature, local expert-

ise, type of equipment available, and the experience of the

radiologists. Given the increasing emphasis on cost-

effective practice, clinicians and radiologists must maxi-

mize the diagnostic and therapeutic yield of procedures

while minimizing costs. Optimal management of critically

ill patients also requires close communication between the

critical care team and the diagnostic and interventional

radiologist. An established practice of daily ICU radiology

rounds with the participation of the radiologist facilitates

this level of communication.

In a traditional model, all ICU films would be placed on

a designated mechanical film alternator within either the

ICU or the radiology department. With rapid advances in

imaging options and telecommunications feasibility, new

models for ICU imaging are being developed. In one model,

films are acquired electronically and displayed in a patient

archival and communications system (PACS) or on Web-

based servers. The PACS unit is able to display plain radi-

ographs, ultrasound and nuclear medicine studies, computed

tomography (CT), and magnetic resonance images (MRI).

Suboptimal exposures may be corrected in part by adjusting

contrast and window levels. High-resolution monitors may

be placed at designated sites in the ICU and throughout the

hospital. An ideal system integrates PACS with the hospital

information system (HIS) and the radiology information

system (RIS) to display clinical and radiologic information.

These systems may greatly improve the efficiency of clini-

cians, nurses, and support staff.

Although neurologic and musculoskeletal imaging stud-

ies play an important role in the care of the critically ill

patient, this chapter will limit discussion to imaging of the

chest and abdomen, with a focus on adult ICU patients.

IMAGING TECHNIQUES

Most radiographic examinations in the ICU are obtained at

the bedside utilizing conventional analog or digital equip-

ment. In most facilities, ultrasound and portable gamma

cameras for planar nuclear medicine studies are useful and

critical adjuncts for bedside examinations in the ICU. Other

imaging methods, including high-quality ultrasound, CT,

nuclear medicine techniques, and MRI, are used selectively

due to cost and transport issues. Interventional procedures,

either at the bedside or in the radiology suite, are also fre-

quently performed under imaging guidance.

Plain Radiography

Digital systems are being used increasingly in the ICU for

portable radiography. With these systems, images are

obtained using a photo-stimulable phosphor imaging plate

instead of film. The exposed imaging plate is scanned, read,

and processed by computer, and the image can be transmit-

ted to an ICU console or viewed as a hard copy on a conven-

tional view box. Chest radiographs are the most common

imaging examination, accounting for approximately 40% of

the volume in a radiology department. As many as one-third

of these chest radiographs may be obtained at the bedside

(portable radiographs), and in the ICU almost all chest radi-

ographs are taken using the portable technique. The utility

and effectiveness of routine daily portable chest radiographs

have been studied, and—despite limitations of the technique—

these films play an important role in identifying and follow-

ing pulmonary and cardiac disorders in ICU patients. Chest

radiographs are also used to evaluate the positions of and

complications from catheters and support devices used in

the care of critically ill patients.

Likewise, imaging of the abdomen generally should begin

with plain radiographs, which provide a readily accessible

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138

means of diagnosing perforation, bowel obstruction, and

ileus. However, because the overall sensitivity of plain radi-

ographs remains low, further imaging with CT may be nec-

essary to confirm suspected perforation and related

complications (eg, abscess) and to inspect the features of the

bowel walls and surrounding fat. Supine radiographs are most

appropriate for verifying nasogastric or feeding tube place-

ment and for investigation of renal stones and possible ileus

or bowel obstruction. Additional views (ie, semiupright, left

lateral decubitus, and cross-table lateral) may be helpful in

cases of bowel perforation, ileus, or obstruction.

Ultrasound

Ultrasound examination at the bedside in the ICU is relatively

inexpensive and does not use ionizing radiation. In the thorax,

ultrasound is used most often to evaluate and localize pleural

fluid collections, to determine whether such collections are

free or loculated, and as a guide to thoracentesis. Ultrasound is

also helpful in clarifying peridiaphragmatic processes because

the diaphragm is easily visualized, allowing differentiation of

supradiaphragmatic and infradiaphragmatic fluid collections.

The greatest utility of ultrasound, however, is in the evalua-

tion of abdominal disease. Ultrasound provides rapid assess-

ment of hepatobiliary and genitourinary disease and may be

used to guide percutaneous drainage of intraabdominal

abscesses. It allows rapid evaluation of the hepatobiliary sys-

tem, gallbladder, kidneys, pelvic organs, and scrotal disorders.

Visualization of vascular perfusion and parenchymal flow is

a useful feature, especially in transplanted organs.

Ultrasound is also indispensable for guidance of bedside pro-

cedures such as central line placement, cholecystostomies,

biopsies, and drainage of fluid collections.

Computed Tomography

By virtue of multiplanar imaging capabilities and improved

contrast resolution, multidetector CT (MDCT) has been

shown to be very valuable in increasing diagnostic accuracy

and guiding therapeutic procedures for critically ill patients.

MDCT allows for more rapid scanning of patients, with

imaging of the entire chest, abdomen, and pelvis with thin

sections during a single breath-hold. Such short acquisition

times have facilitated the use of CT for evaluation of vascu-

lar disorders such as aortic dissection and pulmonary

embolism. CT also allows for improved characterization of

pulmonary diseases, particularly acute respiratory distress

syndrome (ARDS), and is a critical diagnostic tool for the

evaluation of an acute abdomen.

Transportation of the ICU patient to the CT scanner

requires a coordinated effort from hospital personnel, includ-

ing ICU physicians and nurses, respiratory therapists, radiol-

ogy technologists, and radiologists. Careful monitoring

during transport and during the procedure is essential and

must include arrhythmia monitoring and pulse oximetry.

Nuclear Scintigraphy

Nuclear scintigraphy has a number of applications in the

critically ill patient. Myocardial perfusion and infarct scan-

ning in cardiac disease, ventilation-perfusion scanning in

patients with suspected pulmonary embolism, evaluation of

gastrointestinal hemorrhage and acute cholecystitis, and

localization of occult infection are among the most common

indications for radionuclide imaging in the ICU patient.

Magnetic Resonance Imaging

MRI has supplanted CT in the evaluation of many disorders

because it does not employ ionizing radiation, because it pro-

vides excellent differentiation of vascular and nonvascular

structures without the use of intravenous contrast material, and

because it provides cross-sectional images in multiple planes. It

is generally considered the single best imaging method for eval-

uation of the CNS, head and neck, liver, and musculoskeletal

system. However, in many cases, MRI is not feasible in the eval-

uation of the critically ill patient because of interference caused

by ferromagnetic monitoring devices, the difficulty of ade-

quately ventilating and monitoring patients within the narrow

MRI gantry, and long scan times. MRI may be appropriate in

selected diagnostic dilemmas if MR-compatible equipment and

coordinated effort among caregivers can be arranged.

Mayo PH, Doelken P: Pleural ultrasonography. Clin Chest Med

2006;27:215–27. [PMID:16716814]

Nicolaou S et al: Ultrasound-guided interventional radiology in crit-

ical care. Crit Care Med 2007;35:S186–97. [PMID: 17446778]

Redfern RO et al: A picture archival and communication system

shortens delays in obtaining radiographic information in a

medical intensive care unit. Crit Care Med 2000;28:1006–13.

[PMID: 10809274]

Trotman-Dickenson B: Radiology in the intensive care unit (part 1).

J Intensive Care Med 2003;18:198–210. [PMID: 15035766]

Trotman-Dickenson B: Radiology in the intensive care unit (part 2).

J Intensive Care Med 2003;18:239–52. [PMID: 15035758]

IODINATED CONTRAST AGENTS

Adverse reactions to iodinated contrast agents occur at low

rates but are encountered not infrequently given their wide-

spread use. Older ionic agents, newer nonionic agents, and

the newest nonionic isoosmolar agents are available, with

the oldest agents having the highest incidence of adverse

reactions and the newest agents having a significantly lower

incidence. Idiosyncratic reactions range from benign

urticaria to, very rarely, life-threatening hypotension, laryn-

geal edema, and bronchospasm. These events are not consid-

ered truly allergic in nature because they are not

antibody-mediated and are inconsistently reproducible with

subsequent administrations. Pretreatment with corticos-

teroids appears to be effective for mild events, but corticos-

teroids should not be used in patients with a history of severe

reaction. In the latter situation, an alternative such as MRI with

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IMAGING PROCEDURES

139

gadolinium contrast or carbon dioxide angiography should

be considered. Contrary to popular belief, allergy to shellfish

is not predictive of reactions to iodinated contrast agents.

Contrast nephropathy is another important complication

of intravascular iodinated contrast use and occurs in the setting

of preexisting renal compromise, most often due to dehydra-

tion, surgery, nephrotoxic drugs, or long-standing diabetes.

Again, the incidence is highest with the oldest agents and low-

est with the isoosmolar nonionic agents. Although the serum

creatinine level is a convenient measure of renal function, cre-

atinine clearance should be calculated for a more reliable

estimation—less than 25 mL/min or 25–50 mL/min with risk

factors identifying high-risk patients. Potentially effective pre-

ventive strategies include adequate intravenous hydration with

normal saline or sodium bicarbonate solution and administra-

tion of N-acetylcysteine. Metformin should be stopped until

48 hours following contrast use to avoid possible lactic acidosis

in the event of contrast nephrotoxicity. Rather than using a uni-

versal creatinine level cutoff, the decision to use contrast agents

should be made on a case-by-case basis, carefully weighing the

need for the study in high-risk patients. In affected patients, the

serum creatinine level peaks at 4–7 days and gradually normal-

izes. Progression to end-stage renal disease is exceptionally rare.

Bettmann MA: Frequently asked questions: Iodinated contrast

agents. Radiographics 2004;24:S3–10. [PMID: 15486247]

Merten GJ et al: Prevention of contrast-induced nephropathy with

sodium bicarbonate: A randomized, controlled trial. JAMA

2004;291:2328–34. [PMID: 15150204]

Meschi M et al: Facts and fallacies concerning the prevention of

contrast medium-induced nephropathy. Crit Care Med

2006;34:2060–8. [PMID: 16763513]

Tepel M et al: Prevention of radiographic-contrast-agent-induced

reductions in renal function by acetylcysteine. N Engl J Med

2000;343:180–4. [PMID: 10900277]

USE OF CENTRAL VENOUS CATHETERS

FOR CONTRAST INJECTION

Peripheral veins are the preferred routes of contrast agent

administration in imaging. When peripheral access is diffi-

cult, existing central venous catheters (CVCs) may be consid-

ered, with a few caveats. Intraluminal pressure limitations

may result in low contrast flow rates, producing a suboptimal

study, or catheter rupture may occur during rapid power

injection of the relatively viscous contrast material. While

most catheter manufacturers do not provide specific instruc-

tions in this regard and practice standards have not been

established, the following general precautions may be useful:

(1) High flow rates (>2 mL/s) should be avoided in most

temporary or tunneled CVCs, (2) silicone-type peripherally

inserted central catheters (PICCs) should not be used, (3) for

multilumen catheters, the largest-caliber port should be used

when possible, (4) Groshong-valve lines should not be used,

(5) pulmonary or systemic arterial lines should not be used,

and (6) catheter integrity and patency should be checked

before and after injection. Since no established guidelines are

available, hospital personnel should be knowledgeable about

the specific catheters used at their institution.

Funaki B: Central venous access: A primer for the diagnostic radi-

ologist. AJR 2002;179:309–18. [PMID: 12130425]

Salis AI et al: Maximal flow rates possible during power injection

through currently available PICCs: An in vitro study. J Vasc

Interv Radiol 2004;15:275–81. [PMID: 15028813]

Reynolds NJ, Grosvenor LJ: Problems with the rapid powered

injection of radiology contrast through multilumen catheters.

Anaesthesia 2003;58:923–4. [PMID: 12911383]

IMAGING OF SUPPORT & MONITORING

DEVICES IN THE ICU

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Endotracheal & Tracheostomy Tubes

Both endotracheal intubation and tracheostomy may cause

potentially serious complications. Malpositioning of the

endotracheal tube into the right main stem bronchus occurs

in approximately 9% of endotracheal intubations. Such mal-

positioning may lead to atelectasis of the left lung, hyperin-

flation of the right lung, and possible pneumothorax. The

clinical assessment of tube location is frequently inaccurate,

and a chest radiograph should be obtained immediately fol-

lowing intubation. Tubes currently in use are usually radi-

ographically visible by virtue of a metallic wire or barium

marker in the wall of the tube. Periodic radiographs are

required to exclude inadvertent displacement of the tube by

cough, suctioning, or the weight of the respiratory apparatus.

Since endotracheal tubes are typically fixed in position at

the nose or mouth, flexion and extension of the neck may result

in motion of the tube relative to the carina, with the tube

descending during flexion and ascending during extension.

With the neck in neutral position, the ideal position of the tube

tip is 5–7 cm above the carina, which allows for a tolerable

change in tube position during flexion and extension. In 90%

of patients, the carina projects between the fifth and seventh

thoracic vertebrae on the portable radiograph; when the carina

cannot be clearly seen, the ideal positioning of the endotracheal

tube is at the T2–T4 level. The aortic arch also may be used to

estimate tube location because the carina is typically at the level

of the undersurface of the aortic arch. The balloon cuff should

not be greater in diameter than the trachea because cuff over-

inflation can cause pressure necrosis of the tracheal wall.

Inadvertent placement of the endotracheal tube into the

esophagus is uncommon but may be catastrophic when it

does occur. Esophageal intubation may be difficult to diag-

nose on the portable chest film because the esophagus fre-

quently projects over the tracheal air column. Gastric or

distal esophageal distention, location of the tube lateral to

the tracheal air column, and deviation of the trachea sec-

ondary to an overinflated intraesophageal balloon cuff are

radiographic signs of esophageal intubation. The right posterior

oblique view with the patient’s head turned to the right

CHAPTER 7

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allows ease of separation of the esophagus and trachea and

should be obtained in equivocal cases.

Intubation may result in injury to the trachea, with tra-

cheal stenosis developing in approximately 19% of patients

following endotracheal intubation and approximately 65%

of patients with tracheostomy. In patients with translaryn-

geal intubation, the most frequent sites of stenosis are the

cuff site and the subglottic region.

Tracheostomy is typically performed in the patient who

requires relatively long-term ventilatory support. Although

the surgical mortality rate is less than 2%, the long-term

complication rate may be as high as 60%. Pneumothorax,

pneumomediastinum, subcutaneous emphysema, hemor-

rhage, and tube malposition may occur as early complica-

tions, whereas late complications include tracheal stenosis,

tracheo-innominate artery fistula, tracheoesophageal fistula,

stomal infection, aspiration, and tube occlusion. In addition,

the incidence of nosocomial pneumonia is increased second-

ary to airway bacterial colonization.



Central Venous Catheters

Central venous catheters are used frequently in the ICU patient

for venous access, especially for purposes of parenteral alimen-

tation, monitoring central venous pressure, and hemodialysis.

Such catheters are visible on the chest radiograph, and knowl-

edge of normal thoracic venous anatomy is required to assess

catheter location. The subclavian vein, the internal jugular vein,

and the femoral veins are the sites of venous access used most

commonly. Central venous lines inserted via a thoracic vein are

optimally positioned when the tip is past the valves in the sub-

clavian or brachiocephalic veins within the superior vena cava.

The preferred location for hemodialysis or pheresis catheters is

subject to debate, however, because some physicians believe

that catheter durability and performance are improved by

placement of the catheter tip within the upper right atrium.

Union of the subclavian and internal jugular veins to form

the brachiocephalic vein usually occurs behind the sternal end

of the corresponding clavicle. Whereas the right brachio-

cephalic vein has a vertical course as it forms the superior vena

cava, the left brachiocephalic vein crosses the mediastinum

from left to right in a retrosternal position to enter the superior

vena cava. The radiographic location of the superior vena cava

may be assessed relative to the tracheobronchial angle, with the

upper border of the superior vena cava usually just superior to

the angle of the right main stem bronchus and the trachea. The

junction of the superior vena cava and right atrium is at the

approximate level of the lower aspect of the bronchus inter-

medius. Changes in catheter location may occur with change in

patient position and changes in respiration.

Approximately one-third of catheters are incorrectly

positioned at the time of the initial chest radiograph. The

malpositioned catheter tip may result in venous thrombosis

or perforation as well as inaccurate venous pressure readings.

Positioning of the catheter tip within the right atrium may

result in cardiac perforation and tamponade, whereas a right

ventricular location may result in arrhythmias secondary to

irritation of the endocardium or interventricular septum.

Complications of central venous catheterization include

pneumothorax, hemothorax, and perforation, which may

result in pericardial effusion, hydrothorax, mediastinal

hemorrhage, or ectopic infusion of intravenous solutions

(Figure 7–1). Less common complications include air



Figure 7–1. Mediastinal hematoma following attempted central venous catheterization. A. Mediastinum appears

unremarkable prior to catheter placement. B. Following attempted central line placement, there is widening of the

superior mediastinum secondary to mediastinal hemorrhage due to a lacerated subclavian artery.

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IMAGING PROCEDURES

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embolism and catheter fracture or embolism. The incidence of

pneumothorax ranges between 1% and 12% and is higher with

a subclavian approach than with an internal jugular approach.

Pneumothorax may be clinically occult, and a chest radiograph

should be obtained to exclude a pneumothorax following line

placement. A radiograph should be obtained even following an

unsuccessful attempted line placement and is more critical

when contralateral venous cannulation is anticipated to avoid

the development of bilateral pneumothoraces. Although sel-

dom obtained in ICU patients, the cross-table lateral view may

be helpful to localize catheters malpositioned in the internal

mammary or azygos vein or in extravascular positions.

Venous air embolism is an uncommon complication of

central venous catheterization. Radiographically, air in the

main pulmonary artery is diagnostic, but other features include

focal oligemia, pulmonary edema, and atelectasis. Intracardiac

air or air within the pulmonary artery is seen easily on CT.

Long-term complications of venous access devices include

delayed perforation, pinch-off syndrome, thrombosis,

catheter knotting, and catheter fragmentation. Left-sided

catheters have a greater risk for perforation, with increased

risk in catheters abutting the right lateral wall of the superior

vena cava. In pinch-off syndrome, the catheter lumen is com-

promised by compression between the clavicle and the first

rib, leading to catheter malfunction and possible catheter

fracture. This is frequently first observed as subtle focal nar-

rowing of the catheter as it crosses the intersection of clavicle

and rib. As increasing numbers of chronically ill patients with

long-term venous catheters—including liver and bone mar-

row transplant recipients—are transferred to the ICU during

their hospital course, more such complications may be seen.

Access to the central venous system may be achieved

through a peripherally inserted central catheter (PICC)

placed via the antecubital fossa. These smaller catheters

course to the superior vena cava and may be associated with

fewer complications than catheters inserted via the internal

jugular or subclavian approach.



Pulmonary Artery Catheters

The pulmonary artery catheter has enhanced the manage-

ment of the ICU patient, allowing monitoring of left atrial

and left ventricular end-diastolic pressures and calculation of

vital data such as cardiac output and vascular resistance. The

catheter tip should lie within a large central pulmonary

artery; the ideal position for the pulmonary artery catheter is

within the right or left main pulmonary artery, below the

level of the left atrium. The catheter tip when deflated should

not be peripheral to the proximal interlobar arteries.

Complications associated with their use include arrhyth-

mias, pneumothorax, vascular perforation, venous air

embolism, and catheter-related sepsis. Knotting, kinking,

and coiling of the catheter also occur.

Pulmonary infarction, thrombosis, pulmonary artery rup-

ture, and infection represent other major complications asso-

ciated with indwelling pulmonary artery catheters. There is a

7% incidence of pulmonary ischemic lesions due to direct

injury from the use of pulmonary artery catheters. The major-

ity of these lesions are thought to be due to vascular occlusion

by the catheter itself. Continuous wedging of the catheter tip

in a peripheral pulmonary artery and central pulmonary

artery obstruction by the inflated balloon have been cited as

precipitating causes. In a smaller number of cases, emboli

arose from peripheral thrombosis around the catheter.

Pulmonary infarction secondary to a pulmonary artery

catheter has a radiographic appearance like that of infarction

from other causes. Typically, a wedge-shaped parenchymal

opacity is seen in the distribution of the vessel distal to the

catheter (Figure 7–2). The presence of a pleural effusion is

variable. Management consists of removal of the catheter;

anticoagulation is generally not required. Resolution of con-

solidation usually occurs in 2–4 weeks.

Pulmonary artery rupture is a catastrophic complication

of pulmonary artery catheterization, with a reported mortal-

ity rate of 46%. The incidence is low—no more than 0.2% of

catheter placements. Risk factors include pulmonary hyper-

tension, advanced age, and improper balloon location or

inflation. The mortality rate increases in anticoagulated

patients. Pseudoaneurysm formation has been reported sec-

ondary to rupture or dissection by the balloon catheter tip.

This appears radiographically as a well-defined nodule at the

site of the aneurysm, but it may be obscured initially by

extravasation of blood into the adjacent air spaces. Chest

radiographic findings often precede clinical manifestations,

and death due to rupture of pseudoaneurysm may occur

weeks following catheterization. The CT appearance of a

pulmonary artery pseudoaneurysm has been described as a

sharply defined nodule with a surrounding halo of faint

parenchymal density. Pulmonary artery pseudoaneurysm

now may be treated in some patients with transcatheter

embolization rather than surgical resection.

Location of the catheter tip should be monitored with

serial radiographs. Softening of the catheter over time may

result in migration of the catheter tip peripherally.

Redundancy of the catheter within the right heart favors

peripheral migration, and the intracardiac loop gradually

becomes smaller (see Figure 7–2).



Intraaortic Balloon Counterpulsation

Intraaortic balloon counterpulsation is used to improve car-

diac function in patients with cardiogenic shock and in the

perioperative period in cardiac surgery patients. The device

consists of a fusiform inflatable balloon surrounding the

distal portion of a catheter that is placed percutaneously

from a femoral artery into the proximal descending thoracic

aorta. The balloon is inflated during diastole, thereby

increasing diastolic pressure in the proximal aorta and

increasing coronary artery perfusion. During systole, the

balloon is forcibly deflated, allowing aortic blood to move

distally and decreasing the afterload against which the left

ventricle must contract, thus decreasing left ventricular

workload. The timing of inflation and deflation is controlled

by the ECG.

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142

The tip of the balloon ideally should be positioned just dis-

tal to the origin of the left subclavian artery at the level of the

aortic knob, maximizing the effect on the coronary arteries

while reducing the possibility of occlusion of the left subclavian

artery, embolization to cerebral vessels, or occlusion of the

abdominal vessels by the balloon. Complications associated

with the device are most often secondary to malpositioning of

the catheter and include obstruction of the subclavian artery

and cerebral embolism. Aortic dissection has been described,

and an indistinct aorta on chest radiographs has been suggested

as an early clue to intramural location, requiring confirmation

by angiography. Balloon leak or rupture also has been described.



Figure 7–2. Lung infarction secondary to pulmonary artery catheterization. A. Initial radiograph after catheterization

shows the tip of the catheter at the level of the right interlobar pulmonary artery. Mild redundancy of the catheter is present

within the dilated heart. B. At 24 hours, the patient developed hemoptysis. Radiograph now shows migration of the catheter

into a segmental arterial branch with increased density in the right lower lobe. C. Follow-up film demonstrates dense consol-

idation of the right middle and lower lobes secondary to infarction. (Reproduced, with permission, from Aberle DA, Brown K:

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IMAGING PROCEDURES

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

Cardiac Pacemakers and Automatic

Implantable Cardioverter Defibrillators

Cardiac pacemakers can be inserted by three approaches:

transvenous, epicardial, and subxiphoid. Most often the

transvenous approach is used, whereby wires are introduced

via the subclavian or jugular vein and fluoroscopically

guided into the right atrium and ventricle.

When viewed on a chest radiograph, the pacemaker lead

should curve gently throughout its course; regions of sharp

angulation will have increased mechanical stress and

enhance the likelihood of lead fracture. Excessive lead length

may predispose to fracture secondary to sharp angulation or

may perforate the myocardium, and a short lead can become

dislodged and enter the right atrium. Leads also may

become displaced and enter the pulmonary artery, coronary

sinus, or inferior vena cava. When possible, a lateral chest

radiograph is recommended to confirm pacemaker lead

location, with the electrodes located at least 3 mm deep to

the epicardial fat stripe. Other complications include venous

thrombosis or infection, either at the pulse generator pocket

or within the vein. Myocardium perforation may result in

hemopericardium and cardiac tamponade.

Biventricular pacing or cardiac resynchronization therapy is

a relatively new treatment for severe chronic heart failure. In

patients with dilated cardiomyopathy and intraventricular con-

duction delay, biventricular or left ventricular pacing can syn-

chronize contraction and increase cardiac output and exercise

tolerance. Percutaneous lead placement into a coronary vein via

the coronary sinus allows for left ventricular pacing. Many of

these patients also will have intravascular defibrillators because

of the risk of ventricular arrhythmias. The automatic

implantable cardioverter defibrillator (AICD) is used for treat-

ment of ventricular tachyarrhythmias unresponsive to conven-

tional antiarrhythmic drugs. Earlier devices consisted of a fine

titanium mesh placed on the cardiac surface and attached to a

generator source that provided an electrical output in the event

of ventricular arrhythmia. Devices currently in use typically are

combined with a cardiac pacemaker. Radiographs are used to

assess the location of wires.



Nasogastric Tubes

Nasogastric tubes are used frequently to provide nutrition

and administer oral medications as well as for suctioning gas-

tric contents. Ideally, the tip of the tube should be positioned

at least 10 cm beyond the gastroesophageal junction. This

ensures that all sideholes are located within the stomach and

decreases the risk of aspiration. Complications of nasogastric

intubation include esophagitis, stricture, and perforation.

Small-bore flexible feeding tubes have been developed

to facilitate insertion and improve patient comfort.

However, inadvertent passage of the nasogastric tube into

the tracheobronchial tree is not uncommon, most often

occurring in the sedated or neurologically impaired

patient. In patients with endotracheal tubes in place, low-

pressure, high-volume balloon cuffs do not prevent passage

of a feeding tube into the lower airway. If sufficient feeding

tube length is inserted, the tube actually may traverse the

lung and penetrate the visceral pleura (Figure 7–3).



Figure 7–3. Malpositioned feeding tube. A. Feeding tube courses via the right main stem bronchus with the tip

(arrow) overlying the right costophrenic angle. An endotracheal tube is present. B. Following removal of the feeding

tube, a pneumothorax is seen (arrow).

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144

Removal of the tube from an intrapleural location may

result in tension pneumothorax, and preparations should

be made for potential emergent thoracostomy tube place-

ment at the time of removal.

In addition to feeding tubes, balloon tamponade tubes

occasionally are used for nasogastric intubation in the treat-

ment of bleeding esophageal and gastric varices. The balloon

can be easily recognized when distended, and correct posi-

tioning can be evaluated radiographically. Esophageal rup-

ture complicates approximately 5% of cases in which balloon

tamponade tubes are used.



Chest Tubes

Thoracostomy tubes (“chest tubes”) are used for the evacua-

tion of air or fluid from the pleural space. When chest tubes

are used for relief of pneumothorax, apical location of the tip

of the tube is most effective, whereas a tube inserted to drain

free-flowing effusions should be placed in the dependent

portion of the thorax. Chest radiographs, ultrasound, or CT

should be used to guide correct placement of the tube for

adequate drainage of a loculated effusion. Failure of the chest

tube to decrease the pneumothorax or the effusion within

several hours should arouse suspicion of a malpositioned

tube. Tubes located within the pleural fissures are usually less

effective in evacuating air or fluid collections. An interfis-

sural location is suggested by orientation of the tube along

the plane of the fissure on frontal radiographs and by lack of

a gentle curvature near the site of penetration of the pleura,

indicating failure of the tube to be deflected anteriorly or

posteriorly in the pleural space. The lateral view may be con-

firmatory. Uncommonly, thoracostomy tubes may penetrate

the lung, resulting in pulmonary laceration and bron-

chopleural fistula. Unilateral pulmonary edema may occur

following rapid evacuation of a pneumothorax or pleural

effusion that is of long standing or has produced significant

compression atelectasis of lung.

Cascade PN et al: Radiographic appearance of biventricular pacing

for the treatment of heart failure. AJR 2001;177:1447–50.

[PMID: 11717105]

Funaki B: Central venous access: A primer for the diagnostic radi-

ologist. AJR 2002;179:309–18. [PMID: 12130425]

Gayer G et al: CT diagnosis of malpositioned chest tubes. Br J

Radiol 2000;73:786–90. [PMID: 11089474]

Hunter TB et al: Medical devices of the chest. Radiographics

2004;24:1725–46. [PMID: 15537981]

Maecken T, Grau T: Ultrasound imaging in vascular access. Crit

Care Med. 2007;35:S178–85. [PMID: 17446777]

Salem MR: Verification of endotracheal tube position. Anesthesiol

Clin North Am 2001;19:813–39. [PMID: 11778382]

Vesely TM: Central venous catheter tip position: A continuing con-

troversy. J Vasc Intervent Radiol 2003;14:527–34. [PMID:

12761305]

IMAGING IN PULMONARY DISEASES



Routine Daily Chest Radiographs:

Technical Considerations & Utility

Portable chest radiographs are frequently obtained on a daily

basis on ICU patients and as indicated by changes in their

clinical situation. Several factors related to portable radiog-

raphy may lead to difficulty in evaluation of radiographs in

a critically ill patient. The equipment used for portable

radiographs requires longer exposure time than standard

radiographs obtained in the radiology department, some-

times resulting in artifacts due to respiratory, cardiac, and

gross patient motion. Inadequate exposure may result

from the limited power output of portable equipment.

Special attention must be paid to the multiple monitoring

devices required by the ICU patient, and considerable physical

effort by the technologists is required to transport portable

equipment.

Limitations imposed by the portable technique often

complicate image interpretation. Almost all portable chest

radiographs are taken with the patient supine and with the

film placed behind the back of the patient (anteroposterior)

rather than in the conventional upright, posteroanterior

position used in the radiology department. Supine chest

radiographs result in decreases in lung volume and can alter

the size and appearance of the lungs, the pulmonary vascula-

ture, and the mediastinum. Anteroposterior chest radi-

ographs cause cardiac magnification, making evaluation of

true cardiac size more difficult. Inspiratory films may be dif-

ficult to obtain because of respiratory distress, pain, sedation,

or alterations in mental status. These technical limitations

complicate diagnostic interpretation. Nonetheless, portable

radiography continues to be a primary method of imaging

critically ill patients.

The utility of daily radiographs may depend on the

underlying disease process. Routine daily radiographs are

of greatest utility in patients with pulmonary or compli-

cated cardiac disease. The American College of Radiology

Thoracic Expert Panel concluded that daily chest radi-

ographs are indicated for patients with acute cardiopul-

monary problems and those receiving mechanical

ventilation. In patients requiring cardiac monitoring or

stable patients admitted for extrathoracic disease, an ini-

tial admission film is recommended. Additional radi-

ographs are indicated when new support devices are

placed or a specific question arises regarding cardiopul-

monary status.

Krivopal M et al: Utility of daily routine portable chest radiographs

in mechanically ventilated patients in the medical ICU. Chest

2003;123:1607–14. [PMID: 12740281]

Tocino I et al: Routine daily portable x-ray. American College of

Radiology. ACR Appropriateness Criteria. Radiology 2000;215:

S621–6. [PMID: 11037473]



IMAGING PROCEDURES

145



Atelectasis

ESSENTIALS OF RADIOLOGIC

DIAGNOSIS



Shift in position of a fissure or change in position of hila

or mediastinum.



Elevation of hemidiaphragm.



Compensatory hyperexpansion of uninvolved lobes.



Increased opacity of the atelectatic lung.



Air bronchograms.



Narrowing of rib interspaces.

General Considerations

Atelectasis is the most common pulmonary parenchymal

abnormality seen in ICU patients. Signs and symptoms of

atelectasis are nonspecific, and atelectasis may coexist with

other pulmonary diseases. Multiple factors contribute to the

development of atelectasis. In the bedridden patient,

hypoventilation results in atelectasis of the dependent lung.

Central neurogenic depression, anesthesia, or splinting may

decrease alveolar volume, reducing surfactant and promot-

ing diffuse microatelectasis. Bronchial obstruction from

retained secretions and mucous plugging may lead to post-

obstructive collapse of the distal lung, particularly in patients

with pulmonary infection or chronic airway disorders. In the

intubated or postoperative patient, other factors are contrib-

utory. A malpositioned endotracheal tube with right main

stem bronchial intubation can cause atelectasis of the non-

ventilated left lung. Following cardiac surgery, left lower lobe

collapse occurs frequently due in part to the weight of the

heart unsupported by pericardium, which compresses the

left lower lobe bronchus. Phrenic nerve paresis secondary to

intraoperative cold cardioplegia results in diaphragmatic ele-

vation and is also thought to contribute to lower lobe atelec-

tasis. Pleural processes, including pneumothorax and pleural

effusion, may also result in atelectasis.

Radiographic Features

The radiographic appearance of atelectasis depends largely on

the degree and cause of lung collapse. Findings noted on the

chest radiograph in atelectasis range from subtle diminution in

lung volume without visible opacification to complete opacifi-

cation of a segment, lobe, or lung. Dependent atelectasis occur-

ring in supine patients may be demonstrated on thoracic CT

even in healthy individuals but is usually not appreciated on

plain chest radiography. Linear bands of opacity may be seen in

“discoid” or “platelike” atelectasis, whereas a patchy opacity is

seen with atelectasis of lung subtended by a segmental or sub-

segmental bronchus. With more extensive volume loss such as

collapse of an entire lobe or lung, radiographic signs include an

increase in opacity of the atelectatic lung; shift in the position

of a fissure; change in the position of the mediastinum, hila, or

diaphragm; and hyperexpansion of the uninvolved lung

(Figure 7–4). In some cases, signs of volume loss may be absent

because of exudation of fluid into the atelectatic lung.

Air bronchograms are linear lucencies coursing through

opacified lung and represent patent bronchi and bronchi-

oles surrounded by opacified air spaces. Air bronchograms

are radiographically nonspecific and occur in any disorder

in which patent air-containing bronchi are situated within

consolidated lung, including atelectasis, pulmonary edema,

pneumonia, and hemorrhage. The presence of air bron-

chograms is also variable in atelectasis and depends on the

patency of the major airways and the cause of atelectasis.

Air bronchograms may be useful predictors of the effective-

ness of bronchoscopy in patients with lobar collapse.

Patients without air bronchograms are more likely to

demonstrate improvement following fiberoptic bron-

choscopy than those with air bronchograms. The absence of

air bronchograms in lobar collapse suggests that central



Figure 7–4. Atelectasis in a 22-year-old man with

status asthmaticus. The right upper lobe is opaque, and

there is elevation of the minor fissure consistent with

right upper lobe collapse. Areas of increased density in

the left lung are also due to atelectasis. Lucency adjacent

to the left heart border secondary to pneumomedi-

astinum is present (arrow), and there is subcutaneous

emphysema in the right supraclavicular region.



CHAPTER 7

146

airways may be plugged by secretions which by virtue of

their proximal location are amenable to bronchoscopic

removal. In contrast, the presence of air bronchograms sug-

gests that the collapse is more apt to be due to small airway

collapse or peripheral mucous plugs that are not effectively

treated by therapeutic fiberoptic bronchoscopy.

The left lower lobe is the most frequent location of lobar

atelectasis, with collapse occurring two to three times more

often in the left lower than in the right lower lobe. The cause

is uncertain, although many of the factors cited earlier are

contributory. The radiographic features of left lower lobe col-

lapse include a triangular opacity in the retrocardiac region

and loss of definition of the descending aorta and left hemidi-

aphragm—as well as other signs of volume loss outlined ear-

lier (Figure 7–5). Adequate penetration and patient

positioning are important in assessing left lower lobe disease.

Left lower lobe collapse may be falsely diagnosed secondary

to faulty radiologic technique. Cephalic angulation of the

radiographic beam by 10–15 degrees (lordotic positioning)

may cause projection of extrapleural fat onto the base of the

left lung and result in loss of tangential imaging of the apex of

the hemidiaphragm and subsequent loss of definition of the

diaphragm in the absence of left lower lobe disease. In

instances in which patients are examined radiographically

with even a small degree of lordosis, loss of definition of the

diaphragm therefore cannot be assumed to be secondary to

left lower lobe collapse. Ancillary findings, including depres-

sion of the hilum, crowding of vessels, and air bronchograms,

must be used to diagnose true left lower lobe disease.

Unusual appearances of lobar atelectasis may occur and

make diagnosis difficult. Atelectasis with marked volume

loss may be caused by peripheral airway obstruction and is

frequently chronic and easily missed. Atelectasis also may

present as a mass and be confused with tumor. Recognition

of the anatomic alterations described earlier is required for

differentiation.

Many other causes of parenchymal opacification may be

confused with atelectasis, including pneumonia and pul-

monary infarction. In addition to other features previously

discussed, temporal sequence may be helpful in distinguish-

ing atelectasis from other causes of focal parenchymal opaci-

fication. Whereas atelectasis may appear within minutes to

hours and also may clear rapidly, pneumonia and infarction

typically resolve over days to weeks.

Ashizawa K et al: Lobar atelectasis: Diagnostic pitfalls on chest

radiography. Br J Radiol 2001;74:89–97. [PMID: 11227785]

Tsai KL, Gupta E, Haramati LB: Pulmonary atelectasis: A frequent

alternative diagnosis in patients undergoing CT-PA for sus-

pected pulmonary embolism. Emerg Radiol 2004;10:282–6.

[PMID: 15290480]



Pneumonia

ESSENTIALS OF RADIOLOGIC

DIAGNOSIS



May present as lobar pneumonia, bronchopneumonia,

or interstitial pneumonia.



Parapneumonic effusions and cavitation may be present.



Hilar or mediastinal densities may lead to suspicion of

obstruction secondary to underlying malignancy.



In ICU patients, development of new or worsening

parenchymal pulmonary infiltrates may indicate nosoco-

mial pneumonia, especially if accompanied by cavitation.

General Considerations

Patients with severe pneumonia complicated by sepsis, respira-

tory failure, hypotension, or shock are seen frequently in the

ICU. Some patients will have acquired pneumonia outside of

the hospital (community-acquired), but an important problem

is that of nosocomial pneumonia, defined as lower respiratory

tract infection occurring more than 72 hours after admission.

Nosocomial pneumonia is the most common infection leading

to death among hospitalized patients. Factors contributing to

the high incidence of hospital-acquired pneumonias include

endotracheal intubation or tracheostomy, aspiration, and

impaired host defenses. Prior antibiotic therapy promotes col-

onization of the tracheobronchial tree.

Most radiologists sort the radiographic appearance of

pneumonias into three categories that may aid in differenti-

ation: lobar (alveolar or air space) pneumonia, lobular



Figure 7–5. Left lower lobe collapse in a 20-year-old

man with head trauma sustained in a motor vehicle acci-

dent. A triangular region of increased opacity is present

in the retrocardiac region secondary to left lower lobe

collapse. The major fissure is displaced inferiorly (arrow).