Physical examination and imaging of patients in the intensive care unit (ICU) can be difficult. However, The American College of Radiology’s Appropriateness Criteria recommends daily chest radiographs for patients with acute cardiopulmonary problems and for patients on mechanical ventilation. The authors review common findings in thoracic imaging in patients in the ICU as well as the limitations caused by medical devices.
is an Associate Professor of Radiology, University of Miami
School of Medicine, and Director of Diagnostic Radiology, Jackson
Memorial Hospital, Miami, FL.
is a Professor of Radiology and Medicine and Vice Chairman,
Department of Radiology, Oregon Health and Science University,
Although this material has not been published in manuscript
form, some of the material has been presented in part at the
following meetings: "Critical Care Radiology," American Thoracic
Society Annual Meeting, Atlanta, GA, May 2002; "Thoracic ICU
Radiology," Society of Thoracic Radiology Annual Meeting, Miami
Beach, FL, March 2003; "Chest Imaging in the Intensive Care
Unit," University of Miami Symposium: Imaging, Intervention, and
Physical examination is often difficult in the intensive care
unit (ICU) setting and for many years has been complemented by the
portable chest radiograph (CXR). The interpretation of portable ICU
radiographs may also be difficult because of the limitations of
applying optimal radiographic technique in the ICU setting, as well
as the patient's condition and the presence of monitoring and other
devices (either in or on the patient) that might obscure portions
of the chest. Studies have shown a wide range of utility of these
radiographs, and, to date, there have been only limited studies
claiming to document cost-effectiveness.
According to some studies, 43% to 65% of all ICU CXR had
"unexpected or ab-normal findings,"
many of which affected management. If limited to a "routine" daily
CXR, efficacy decreased to 15% to 18% in a medical or respiratory
ICU setting and decreased even further (5%) in the cardiothoracic
ICU. In pediatric ICUs, 45% of daily radiographs led to
interventions being performed; smaller, more critically ill
children with one or more life- support devices were the most
common patients to undergo such interven-tions.
The American College of Radiology has addressed these issues in
its Appropriateness Criteria,
stating that a daily CXR is indicated for patients with acute
cardiopulmonary problems and for patients on mechanical
ventilation. In patients with a central venous catheter, a
Swan-Ganz catheter, a feeding tube, or a chest tube placement, only
postprocedure radiographs are indicated. Stable cardiac monitoring
patients and those with purely extrathoracic disease require only
admission films upon entry into the ICU.
Atelectasis is the most common cause of lung opacity in an ICU
patient. There is an increased incidence after general anesthesia
and thoracic/upper abdominal surgery. The incidence is also
increased in patients with pre-existing lung disease, smokers,
obese patients, and the elderly. The left lower lobe is the most
common location. In many cases, the atelectasis is linear or
plate-like. However, atelectasis may be patchy and may mimic
pneumonia. In recumbent patients, radiographic evidence of volume
loss may not be evident and differentiation of atelectasis from
consolidation can be difficult. In lobar atelectasis, the presence
or absence of air bronchograms is useful to determine the potential
effectiveness of therapeutic bronchoscopy.
If air bronchograms are present, the atelectasis is most likely
related to the collapse of small airways, and bronchoscopy likely
will not be therapeutic. However, if air bronchograms are absent in
lobar atelectasis, mucoid impaction is the most likely etiology and
therapeutic bronchoscopy has a high likelihood of being beneficial
Pulmonary edema is one of the most common abnormalities
affecting ICU patients. Causes of edema are broadly grouped into 2
categories: 1) hydrostatic edema, including heart failure,
overhydration, and renal failure; 2) permeability edema, including
adult respiratory distress syndrome (ARDS), sepsis, drug reaction
or allergy, near drowning, smoke or toxic fume inhalation,
neurogenic edema, aspiration, fat embolism, and others.
The first radiographic sign of hydrostatic imbalance is
engorgement of the pulmonary veins, reflecting an elevation in left
ventricular end-diastolic pressure (LVEDP). Cephalization of the
vasculature is not very helpful in the ICU setting because many
films are obtained in the supine position, which redistributes
vascular volumes. Nevertheless, a study of 135 supine ICU patients
found that pulmonary wedge pressures >18 mm Hg could be detected
by a vascular pedicle (mediastinal width at the superior vena cava
[SVC]) measuring ≥70 mm and a cardiothoracic ratio (the width of
the heart to the width of the lungs at the bases) of ≥55%, yielding
a 70% accuracy.
These results were better than subjective interpretation of the
films without (56%) or with (65%) clinical data. The true edema
phase is first characterized by interstitial fluid, manifested by
indistinct vessel margins, thickening of bronchi, Kerley lines (A,
B, or C), hazy or "ground-glass" opacities, and a gravity-dependent
increase in density (particularly on CT scans). Pleural effusions
begin to accumulate as interstitial fluid overloads the venules and
lymphatics of the interstitium. Effusions may be bilateral or only
right-sided; a solely left-sided effusion suggests a superimposed
process (or gravity). Interstitial edema is radiographically
indistinguishable from infections, such as pneumocystis and
cytomegalovirus pneumonias, but daily changes are suggestive of
edema rather than infection. Edema with the highest LVEDP manifests
as alveolar opacification, typically bilateral and reasonably
symmetric. However, there are many reasons for asymmetric edema,
including gravity (eg, bedridden, immobile patients), underlying
lung disease that alters blood flow (eg, chronic obstructive
pulmonary disease, fibrosis), cardiac disease (eg, mitral
regurgitation) (Figure 2), pulmonary vascular disease (eg, shunts,
pulmonary embolism, hypoplastic vessels), and re-expansion after
thoracentesis or pneumothorax evacuation (Figure 3). Alveolar edema
may be indistinguishable from hemorrhage or diffuse pneumonia.
After cardiac surgery, patients generally exhibit at least mild
edema, but they typically improve daily.
Permeability edema (often called noncardiogenic) lacks the
pulmonary venous engorgement noted above. An advanced form of
permeability edema, ARDS, is defined by decreased lung compliance,
normal LVEDP, and hypoxia refractory to O
. Initially, there may be no abnormalities on the CXR (up to 12
hours postinsult). Subsequently, the radiograph shows a pattern of
edema (at 12 to 24 hours), which is usually patchy, although it can
progress to diffuse disease (36 to 72 hours). Air bronchograms are
and help distinguish ARDS from hydrostatic edema (Figure 4).
Additionally, Aberle et al
found that 87% of hydrostatic and 60% of permeability edema could
be correctly identified, with a patchy peripheral distribution seen
in 58% with permeability edema but only 13% with hydrostatic edema.
Decreased lung volumes are frequently observed. Pleural effusions,
if present, are usually small. Radiographic findings of barotrauma
are common (see below). Adult respiratory distress syndrome
progresses from an exudative to an organizing phase, which can lead
to a pattern of interstitial fibrosis that may be fixed or may
Aspiration is very common in ICU patients. Aspiration and its
consequences can be divided into 3 forms: Aspiration pneumonitis,
aspiration pneumonia, and obstruction of a central airway. The
severity of aspiration is related to the volume and type of the
aspirate. Factors that increase the risk of aspiration in an ICU
patient include general anesthesia, depressed consciousness,
neuromuscular disorders, esophageal disease, and the presence of a
nasogastric (NG) tube or an endotracheal tube. Focal or multifocal
consolidation in a dependent location is the most common
Poorly defined nodules in an airway distribution resulting from
acinar filling are often identified (Figure 5). Airway thickening
and plugging, as well as associated volume loss, are also commonly
identified. Aspiration pneumonitis may progress over the first day
but should show clearing within the first few days. A lack of
clearing or progression is suggestive of the development of
pneumonia. In the recumbent patient, the aspiration is typically
located in the posterior aspects of the upper lobes, the superior
segments of the lower lobes, and the posterior basilar segments of
the lower lobes. This distribution results in a central
predominance on the anteroposterior (AP) supine radiograph.
Most pneumonia in the ICU are due to either mixed anaerobic or
aerobic gram-negative organisms. They are commonly related to
aspiration. Opportunistic infection should be considered if the
patient is immunosuppressed. The incidence of pneumonia in the ICU
is approximately 10%; however, in patients with ARDS, the incidence
has been reported to range from 20% to 60%, with a 70% incidence at
Although pneumonia is commonly present in patients with ARDS, the
CXR radiograph is only 30% to 50% accurate.
The CXR typically shows patchy areas of consolidation or poorly
defined opacities that are often multifocal (Figure 6). Air
bronchograms are helpful in the diagnosis of pneumonia, but they
may also occur in areas of atelectasis. When present, cavitation is
a more specific finding of pneumonia. Radiographic changes in
pneumonia typically occur more slowly than in atelectasis,
aspiration, or pulmonary edema.
An estimated 4% to 15% of patients on ventilators develop
barotrauma, manifesting as abnormal air collections in the chest.
Underlying lung disease, such as pneumonia and especially ARDS,
raise the risk significantly. The effects of barotrauma are
generally more severe in children and adults up to age 40. The
major factors associated with development of barotrauma include a
peak inspiratory pressure >40 cm H
O, the use of positive end-expiratory pressure (PEEP), and an
inappropriately large tidal volume. Positive pressure ventilation
affects the CXR in a number of ways. The CXR visually improves with
PEEP and "sighs," especially in edema. Positive end-expiratory
pressure improves aeration mostly in the nondependent lung; a
mildly abnormal lung fares better than do dense consolidations and
dependent regions. The heart size decreases, as does the cardiac
output. Pulmonary vessels may decrease or increase in size.
Interstitial pulmonary edema has a protective effect against
barotrauma because of the elevated interstitial pressures.
The initial abnormal air collection in barotrauma is pulmonary
interstitial emphysema (PIE), most often identified in children.
Streaky lucencies radiate from the hila, without branching or
tapering as do air bronchograms. The gas collections can grow into
bubbles, clefts, and cysts between 1 and 8 cm in size. Cysts may
resolve or persist and can become superinfected. Patients with ARDS
frequently develop cysts at the lung bases. Pulmonary interstitial
emphysema carries a significant risk of pneumothorax (77%) from
rupture of a cyst.
The risk of PIE spreading to the mediastinum is 37%.
Pneumothorax (PTX) is the most concerning sequela of barotrauma.
It occurs in up to 25% of ventilated patients, and the risk
increases with increased time on the ventilator. Pneumothorax is
often associated with, but not caused by, pneumomediastinum. In the
supine patient, PTX is usually anteromedial or subpulmonic (lucent
upper quadrants of the abdomen, sharp superior surface of the
diaphragm, deep sulcus sign, and visualization of the inferior
surface of consolidated lung). Less often, the PTX is apical,
lateral (displaces the minor fissure from the chest wall), or
posteromedial. If PTX is suspected but not definite on supine CXR,
then upright, expiratory, or bilateral decubitus radiographs should
be obtained (Figure 7). False-positive appearances of PTX may be
due to skin folds, overlying tubing/dressing/lines, and prior chest
tube tracks. The size of the PTX is unrelated to its significance,
since even a tiny PTX can acutely enlarge in ventilated patients.
Tension is present in 60% to 96% of ventilated PTX cases
and signifies that pleural pressure exceeds atmospheric pressure.
Mediastinal shift is not always present in tension PTX, possibly
masked by PEEP. Signs of tension include displacement of the
anterior junction line, azygoesophageal recess, and flattening of
heart and vascular shadows.
Pneumomediastinum is important as a general sign of barotrauma
and must be distinguished from a PTX. Except in rare cases of
tension, pneumomediastinum is not a life-threatening condition.
Pneumothorax, pneumopericardium, and the Mach effect all mimic
pneumomediastinum. Pneumomediastinum may show air streaking into
the neck, a "continuous diaphragm," and/or retroperitoneal air.
Other manifestations of barotrauma include subcutaneous air and
Pleural effusions are common in patients in the ICU. The supine
CXR shows only moderate (67%) accuracy for identifying effusion,
which is improved on lateral and decubitus films. What appears to
represent pleural effusion on a portable upright film may, in fact,
represent atelectasis (Figure 8).
Pleural effusion is difficult to characterize on plain films,
except in certain settings. Sudden large effusions suggest
hemothorax in a postprocedure patient. Empyema may appear as a
loculated (nonmobile) effusion in a patient with fever. After
cardiac surgery, effusions are common, particularly as pulmonary
edema moves into the pleural space. However, increasing effusion
past the third postoperative day may signal a postpericardiotomy
syndrome, especially if pericardial effusion and pulmonary opacity
Monitoring and support devices
Endotracheal and tracheostomy tubes
The tip of the endotracheal tube should ideally be 4 to 6 cm
above the carina with the neck in a neutral position. If the neck
is flexed, the tube can migrate up to 2 cm inferiorly, while
extension of the neck can cause migration of the tube up to 2 cm
superiorly. If the endotracheal tube is advanced too far, it will
typically extend into the right main bronchus (Figure 9). The
balloon should be assessed to ensure that it is not overinflated.
The balloon should not be greater than the diameter of the trachea.
A ratio of the cuff to tracheal lumen >1.5 leads to an increased
risk of tracheal damage. Aspiration can occur in up to 8% of
patients with endotracheal tubes. Other complications of
endotracheal tube placement include dislodging of teeth or
fillings, tracheal rupture, and tracheal stenosis, as a chronic
Flexion and extension of the neck do not affect the position of
a tracheostomy tube. The tip of the tracheostomy tube should be at
approximately the T3 level. The balloon should not distend the
tracheal wall and the lumen of the tracheostomy tube should be
approximately two thirds of the tracheal diameter.
Feeding and nasogastric tubes
The most important consideration is to ensure that NG tubes,
especially those through which feeding occurs, are positioned in
the stomach or distally and not within the respiratory tree. Often,
a patient will have both suction and feeding tubes, and a request
to "check NG tube placement" should prompt a search for both types
Cardiovascular catheters and other intravascular
The tip of a central venous catheter should be between the right
atrium and most proximal venous valves. The proximal venous valves
2.5 cm distal to the junction of where the subclavian and
jugular veinsmeet to form the brachiocephalic vein. Therefore, a
central venous catheter tip should be medial to the first anterior
rib or beyond. Aberrant placement of central venous catheters
include placement into normal smaller branch veins or anomalous
veins, such as a persistent left SVC. Other important complications
include intra-arterial or extravascular placement (Figure 10). The
radiograph should also be assessed for the presence of a
pneumothorax or hemothorax.
Pulmonary artery catheters (Swan-Ganz catheters) measure
pulmonary artery and capillary wedge pressures. The tip should be
in the main right or left pulmonary artery and should not be distal
to the proximal interlobar pulmonary artery. Approximately 24% of
these catheters are malpositioned on the initial CXR and need to be
Complications include pulmonary infarction, pulmonary artery
rupture, cardiac perforation, intracardiac knots, and
Intra-aortic balloon pumps (IABP) are used for the treatment of
cardiogenic shock. These devices increase coronary perfusion and
decrease cardiac afterload. The balloon deflates in systole and
inflates in diastole, when it may occasionally be seen as a tubular
lucency on the radiograph. The tip should be just distal to the
left subclavian artery in the proximal descending aorta,
approximately 1 to 2 cm below the top of the aortic arch.
Too proximal or too distal positioning may lead to
Chest CT in the ICU
CT scanning is increasingly being used in critically ill
patients who may have multiple medical problems that may not be
easily discriminated by the CXR. It has been estimated that 24% to
75% of ICU chest CTs show "clinically useful" information,
translating to a change in management in 22% to 39% of scanned
However, there remains the risk and cost of transporting patients
from the ICU to the scanner and back.
Major categories in which chest CT has proven useful are:
Mirvis et al
found that 30% of trauma ICU CT showed significant effusion with
possible empyema. Pleural enhancement with contrast suggests an
exudative process, such as hemorrhage, empyema, or tumor. Further-
more, CT is far superior in quantifying effusions as compared with
CT may detect unsuspected pneumonia or tumor. CT is far superior to
the CXR for detecting cavitation, and, therefore, can help identify
abscess and differentiate it from empyema (Figure 11).
Life support devices--
CT revealed that chest tubes were malpositioned in 15% of cases.
Complications of mechanical ventilation
Although seen on CT, 40% of PTX, 70% of bullae, and 80% of
pneumomediastinum were not seen on CXR.
Unsuspected PTX was found in 7% of ventilated patients by CT.
Contrast-enhanced CT is becoming a primary test in patients with
possible pulmonary embolism, a disease of particular concern in
patients experiencing extended hospitalization, such as those in
PACS and the ICU
While the installation and integration of a picture archival and
communications system (PACS) into daily practice primarily benefits
the radiologist in terms of efficiency and workflow, its improved
image accessibility and availability allow clinicians, including
intensivists, to more easily review the radiographic studies they
order. As expected, a study on the presence of PACS workstations in
an ICU setting reported decreased time from the radiograph order to
In order to maintain or improve the benefit of radiologist input on
patient care, timely reporting and/or routine
radiologist-intensivist "rounds" or consultation become
increasingly important. PACS workstations located within ICU
settings are often installed with suboptimal viewing conditions.
For example, bright rooms with excessive ambient light and glare
may render accurate diagnosis difficult in some instances.
Radiologist consultation should be requested when installing new
PACS workstations outside of the radiology department in order to
optimize the viewing environment, including lighting, ergonomics,
and software menu/toolbar layout.
Thoracic imaging, especially using chest radiography, is a
crucial component of intensive medical care. Although specific
radiographic diagnoses are sometimes difficult to make, the
radiograph provides important information about disease
progression, and radiographic findings often lead to changes in
management. The radiograph is invaluable for verification of life
support devices. Computed tomography is particularly useful when
radiographic findings are equivocal or are at odds with the