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centage of treatment alterations affecting outcome. 7' 16, 2 Changes in the treatment or diagnostic approach to patients based on radiographic findings occur following 37% to 65% of all examinations, with 24% to 37% of "routine" studies resulting in changes. Nevertheless, the inappropriate use of imaging is to be avoided because of cost implications. It has been shown that guidelines for the appropriate use of portable radiography can be developed, 11 and it is recommended that multidisciplinary teams develop similar guidelines. Once images are obtained, it is imperative that prompt, accurate interpretations are rendered and communicated, particularly in light of the high percentage of unsuspected findings. Success in meeting this challenge depends on a cooperative effort between the clinical and radiologic teams. Providing adequate clinical information and including the reason for the examination aids the radiologist in making the best possible diagnosis. On the other hand, the radiology service should provide on-line film interpretation to the extent that is possible logistically. Bitetti and Zimmerman9 describe the concepts of such a team approach and cite references indicating positive benefits, including improved diagnostic information, facilitated sequencing of studies, and a decrease in the duration of hospital stay without increased mortality or morbidity because of missed diagnoses. Portable radiography has limited diagnostic capabilities for many reasons, including the limited power output of portable equipment, the inability to obtain motion-free films with full inspiration consistently, inconsistent filming technique, and the inability to position patients upright in many circumstances. Thus, imaging technology other than portable radiography has a place in the care of these patients and may be underutilized. Clinical questions regarding possible empyema, lung abscess, mediastinal abnormality, or other diagnostic dilemmas may require transportation of patients to the radiology department for computed tomography, despite the logistical difficulties in transporting and maintaining the life support systems of these patients. Portable ultrasonography has a well-defined role in diagnosis, especially in the diagnosis and percutaneous treatment of acute cholecystitis, pleural effusions, and empyema. FILM ANALYSIS

Interpreting films on ICU patients can fill the inexperienced with uncertainty and apprehension. The radiographs often reveal extensive abnormalities and the presence of multiple technical devices. A systematic process of evaluating the radiographs is essential to arrive at an accurate interpretation. All tubes and lines should be identified and their locations noted. The musculoskeletal structures and visualized portions of the abdomen should be assessed, a comprehensive evaluation of the cardiovascular status undertaken, and the lungs, pleural space, mediastinum, and diaphragm studied sequentially.

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Figure 1. Anteroposterior portable supine radiograph depicts catheters in place on a patient undergoing extracorporeal membrane oxygenation (ECMO) for respiratory failure following trauma and adult respiratory distress syndrome. A right carotid cannula for arterial access is present (arrowhead). Venous access tubes in the superior vena cava (short arrow) and the inferior vena cava (long arrows) are also in place.

relatively simple and can be instituted at the bedside. Basically, deoxygenated blood is drawn from the venous system, undergoes extracorporeal oxygenation, then is returned to either the arterial or venous system. The two forms of bypass are veno-arterial and venovenous. Arterial access typically is through the right carotid artery or the common femoral artery, and venous access is through the right internal jugular vein, although a femoral vein frequently is used. Use of the jugular vein or carotid artery requires vessel ligation. Evaluation of portable chest radiographs requires a careful analysis of the position of the access lines (Fig. 1) and careful inspection for complications, including barotrauma and hemorrhage. Barotrauma occurs frequently because of the high ventilatory pressures required with noncompliant lungs. Another device recently introduced for direct oxygenation of blood is the IVOX (CardioPulmonics, University of Utah Research Park, Salt Lake City, UT) intravenous oxygenator. This new catheter is placed in the inferior vena cava (Fig. 2). Pure oxygen is passed into the device through hollow fibers composed of gas transfer membranes that permit exchange of oxygen and carbon dioxide. Clinical trials have begun on human subjects with severe, potentially reversible respiratory failure, with promising early results. 21 EVALUATION OF THE CARDIOVASCULAR STATUS

A comprehensive evaluation of the cardiovascular status should be undertaken, including assessment of systemic blood volume, pulmonary blood volume, central venous pressure, pulmonary arterial pres-

ASPECTS

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Figure 3. A, A chronic renal failure patient with overhydration induced pulmonary edema. Arrowheads depict the margins of a wide vascular pedicle indicative of an increase in the circulating blood volume. White arrows show a wide azygos vein on end secondary to elevation of the central venous pressure and also reflecting the increased circulating blood volume. Two black arrows demonstrate a pulmonary artery and its adjacent bronchus on end. B, This portable radiograph was obtained following correction of the overhydrated state. The vascular pedicle (arrowheads) and the azygos vein (arrows) have returned to a normal diameter. The lungs are now clear and the heart size has decreased.

ameter throughout the lungs. As a corollary, decreased flow is recognized when vessel diameters are constricted. 27 By observing the diameters of an adjacent bronchus and pulmonary artery seen on end, the ratio between the diameters of these two structures can be used as a determinant. 44 Under normal circumstances, the pulmonary artery-tobronchus ratio is approximately 1: 1 or less. An increase in this ratio demonstrated throughout the lungs reflects increased pulmonary blood flow, whereas a generalized decrease indicates reduced pulmonary blood volume. Once an estimation of circulating blood volume and pulmonary blood volume is made, a comparison of these two volumes can be used to suggest clinical diagnoses and to guide effective treatment. Incremental widening of the vascular pedicle, associated with a generalized increase in the diameter of pulmonary vessels and a concomitant increase in the transverse cardiac diameter, for example, leads to a diagnosis of fluid overload (Fig. 3A,B). Subsequent response to treatment can be based not only on the physical examination and symptoms of the patient, but also on serial radiographs. Discrepancy between systemic and pulmonary blood volume also can suggest a diagnosis. A combination of vasoconstricted pulmonary vessels and a wide vascular pedicle, for example, suggests the diagnosis of cardiac tamponade. Reduced right ventricular output is the explanation for decreased pulmonary blood flow, whereas widening of the vascular pedicle occurs because of obstruction to central venous return. On the other hand,

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Figure 4. A portable radiograph of a 19-year-old male with an atrial septal defect and a 3 to 1 left to right shunt. Note the dilated pulmonary vessels in the hilar regions indicating increased pulmonary blood flow. The narrow vascular pedicle (arrowheads) indicates decreased or low normal circulating blood volume. This combination indicates the presence of a left to right shunt.

increased pulmonary blood flow in conjunction with normal or decreased systemic blood volume suggests a left-to-right intracardiac shunt, such as a congenital septa! defect (Fig. 4) or acquired rupture of the interventricular septum following myocardial infarction. Pulmonary arterial pressure can be estimated by observing the diameter of the central pulmonary arteries compared with the diameter of peripheral vessels. Several methods are available and, depending on the method used, correlation coefficients ranging up to 0.87 have been reported. 29 These observations do not distinguish acute variations in pulmonary artery pressure that occur in unstable patients, but instead predict a range of pressures in the steady state based on chronic physiologic alterations due to increased vascular resistance. Left ventricular function can be assessed by analyzing the appearance of the pulmonary vessels and the interstitium of the lung. There has been considerable controversy concerning the accuracy and validity of using portable chest radiographs for this purpose. It is important to understand the points of controversy in comprehending the place of radiography in this assessment. In upright patients with normal cardiovascular function, the diameter of the lower lobe vessels is larger than those in the upper lobes, because of preferential blood flow to the lung bases caused by gravitational variation in the hydrostatic pressure from the bottom to the top of the lungs. The vessel margins normally are sharply demarcated. Several studies demonstrated a change in this vascular pattern when pulmonary capillary wedge pressure (PCWP) is elevated. 2s, 4 o As PCWP rises above the normal mean value of 12 mm HHH-rig,vessel diamefers m the upper and-lower lung zones begin to equalize. As PCWP rises further, pulmonary blood flow is redistributed into

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Figure 5. An elderly patient with coronary artery disease and left ventricular failure. A, A portable radiograph demonstrates relative dilatation of upper lobe pulmonary vessels indicating mild elevation of the pulmonary capillary wedge pressure. B, Homogeneous airspace opacities in the central lung zones indicate the presence of alveolar pulmonary edema on this follow-up portable radiograph. The azygos vein has widened (arrowheads) and the vascular pedicle has increased in width (short arrows) indicating increased circulating blood volume and elevation of the central venous pressure.

the upper portions of the lungs (Fig. SA). This is recognized by the presence of larger vessels in the upper lung zones versus vessels in the lung bases. This phenomenon frequently is referred to as cephalization of pulmonary blood flow. When the PCWP rises even further, into the range of 18 to 2S mm Hg, the colloid osmotic pressure of blood is exceeded and transudation of fluid into the interstitium of the lung begins. This accumulation of fluid surrounding the pulmonary vessels results in the radiographic finding of "perivascular cuffing," with blurring of pulmonary vessel margins. Similarly, interstitial fluid accumulates around bronchi, manifesting radiographically as thickened bronchial walls with indistinct margins or "peribronchial cuffing." Fluid also gathers and thickens the interlobular septae, resulting in linear opacities that extend to the pleural surface, particularly near the costophrenic angles, the so-called Kerley B lines. Kerley A lines are longer and central. Kerley C lines represent an overlay of multiple superimposed Kerley A and B lines, but rarely are recognized on portable chest radiographs. As PCWP elevates above 2S mm Hg, transudates collect in large amounts in both the interstitial and alveolar compartments of the lungs, producing alveolar pulmonary edema. This is recognized by hazy, fluffy opacification of the lung, particularly in the central lung zones (see Fig. SB). The amount of extravascular lung water can be estimated. 27, 34 Patients with physiologic amounts of lung water (approximately SO mL/L of lung water at total lung capacity) have well-defined pulmonary

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vessel and bronchial margins. When perivascular and peribronchial cuffing occurs, there is 60 to 100 mL/L lung water at total lung capacity. Alveolar fluid begins to appear when the value rises to 110 to 130 mL/L, with widespread airspace edema at values of more than 160 mL/L. Discrepancies between the degree of heart failure demonstrated on chest radiographs and actual measurements of PCWP are common. Herman et al1 7 found that 38% of patients with left ventricular enddiastolic pressures greater than 20 mm Hg had no radiographic evidence of congestive heart failure. Others12' 22 also have noted discrepancies in the estimation of PCWP in subgroups of patients with acute myocardial infarction and acute left ventricular failure. There are many theoretical explanations for these discrepancies. Pre-existing emphysema, interstitial lung disease, or inability of the patient to attain total lung capacity for the radiograph are factors that may explain these differences. Whereas hemodynamic measurements reflect an instant in time, movement of water in and out of the extravascular compartment may take hours or even days. This lag phase may explain the differences between hemodynamic measurements and the radiographic findings. An assessment of the blood flow in the upper lung zones compared with the bases cannot be made on many patients, given that they often are critically ill, on life-support devices, and, for these reasons, examined in the recumbent or semi-erect position. Woodring45 attempted to circumvent this limitation by studying the relationship between the diameter of the pulmonary artery and its adjacent bronchus on patients in the supine and upright positions (see Fig. 3A). When patients are supine, hydrostatic differences occur from the dorsal to the ventral aspects of the lungs rather than from the lung bases to the lung apices; the arterial- bronchus ratios therefore are equalized throughout the lungs at approximately a 1: 1 ratio under normal circumstances. When PCWP is elevated, the ratio increases throughout the lungs. This allows distinction between left ventricular failure and normal physiology. This ratio cannot distinguish increased pulmonary blood flow from left ventricular failure, however, because both produce an increase in the pulmonary arterial-bronchus ratio. The technique also is severely limited because of the frequent inability to clearly identify adjacent pulmonary arteries and bronchi on end. Extravascular soft tissue water can be estimated by recognizing serial changes in the thickness of the chest wall. This parameter can be used only when patients are positioned consistently and when the chest wall is included in the field of view. A retrospective study correlating changes in chest wall thickness with body weight in renal failure patients showed a correlation coefficient of r = 0.56.27 In summary, the chest radiograph is a valuable tool in the assessment of cardiovascular status. To reach the most accurate assessment possible, a comprehensive evaluation of several parameters, including systemk.blood volume,-pulmonary blood volume, pulmonary vascular flow patterns, and extravascular water should be undertaken, and the findings correlated with the clinical symptoms and physical findings .

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EVALUATION OF PULMONARY DISEASE

Pulmonary parenchymal disease processes in the critically ill often are multiple and difficult to diagnose. Given the technical limitations of portable chest radiography, it is difficult to differentiate the cause of disease and distinguish changes in the disease process from film to film. By carefully correlating the morphology, distribution, and evolution of the radiographic findings with the clinical setting of the patient, however, the cause of the disease process often can be determined. This section delineates imaging features that aid in the differentiation of pathologic processes that produce abnormal pulmonary opacities on portable chest radiographs.

Atelectasis

Loss of aerated lung volume has several radiographic manifestations, including band-like opacities representing subsegmental atelectasis, segmental opacification with or without air-bronchograms, and lobar collapse. The radiograph may even be entirely normal, yet the patient may have physiologically significant intrapulmonary shunting secondary to decreased air exchange and pulmonary vasoconstriction. 43 In addition to visualizing the radiographic opacity of the atelectatic lung, secondary signs of volume loss may be present, including displacement of fissures, mediastinal structures, and the hemidiaphragms, and crowding of the bronchovascular structures and ribs. Subsegmental atelectasis typically has a linear or plate-like configuration. 43 Segmental and lobar atelectasis may appear as patchy, ill-defined opacity or lobar consolidation, often indistinguishable from pneumonia, especially if air-bronchograms are present. This can result in the overdiagnosis of infection as the cause of the radiographic abnormality. Atelectasis without air-bronchograms suggests the presence of an endobronchialobstructing lesion, typically a mucous plug, with retention of secretions within the airways distal to the obstructing lesion. 33 These patients benefit from bronchoscopy, unlike patients with atelectasis and airbronchograms15 of nonobstructive atelectasis. Identifying secondary signs of volume loss or a change in the radiographic findings over minutes to hours favors atelectasis over pneumonia, the latter evolving and improving over a period of days to weeks. The location of the radiographic abnormality also is useful. The left lower lobe is the most frequent site of atelectasis in the critically ill patient, occurring 66% of the time, compared with the right lower lobe, 22%; and the right upper lobe, 11%. 38 It is well known that the left lower lobe is the most common location for both atelectasis and pneumonia following cardiac surgery, secondary to stretching and cold-induced injury of the phrenic nerve. 8 Radiographic technique is important because underpenetrated radiographs result in excess noting of abnormality. With as little as 10 degrees lordotic angulation of the x-ray beam, the

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Figure 6. Cytomegalovirus (CMV) pneumonia. Diffuse bilateral airspace disease with air bronchograms in a 29-year-old HIV positive male. Note the normal size of the heart, azygos vein, and vascular pedicle, and the lack of pleural effusions. '

'j beam is no longer tangential to the apex of the hemidiaphragm and a pseudoconsolidation may appear. 47 Infection

Pneumonia often is difficult to diagnose in the critically ill. Fever and leukocytosis, the hallmarks of infection, may be absent, especially in patients receiving anti-inflammatory medications, the debilitated, and the immunocompromised. Fever is not a reliable indicator of infection, and is present in at least 50% of patients with atelectasis and no pneumonia. 36 The radiographic hallmark of pneumonia is airspace consolidation with air-bronchograms, whether segmental, lobar, or diffuse (Fig. 6). The radiographic false-negative misdiagnosis rate is especially prevalent in the setting of adult respiratory distress syndrome (ARDS), in which it may be as high as 29%. 3 Because of the difficulty in diagnosing pneumonia in this setting, and in separating patients as colonized versus infected, Mock et al in 198831 reviewed the clinical variables and radiographic findings of 80 patients with positive sputum cultures. The chest radiograph was scored with one point each for the presence of new airspace shadows, air-bronchograms, segmental infiltrates, asymmetric infiltrates, infiltrates in nondependent lung, ipsilateral pleural effusion, and absence of volume loss, cardiomegaly, and hilar enlargement. Patients with radiographic findings indicating a moderate or high probability -of pneumonia-tscores 4-10) were-more-likely to have positive blood and fluid cultures, polymicrobial cultures, multisystem organ failure, Escherichia coli or Pseudomonas infection, and improvement

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on antibiotic therapy, than patients with low probability radiographs. Clinical symptoms of fever, leukocytosis, respiratory failure, and mortality did not correlate with the radiographic findings. Nosocomial pneumonia more often is complicated by empyema and lung abscess than is community acquired pneumonia. In the critically ill patient, extensive lung disease and frequent supine or semi-upright films make it difficult to identify pleural collections that could benefit from drainage. Furthermore, drainage is most successful when an infected collection is detected early. 39 A high index of suspicion therefore should be maintained, on both a clinical and radiographic basis. Unfortunately, many fluid collections are unrecognized until they become quite large, with an organized fibrotic rind. When posteroanterior (PA) and lateral upright films are possible, identification of an air-fluid level can identify and distinguish lung abscess from pleural empyema. An air-fluid level of equal width on both views suggests that the abnormality is within the lung, whereas an air-fluid level that is narrow on one view and broad on the other as it parallels the chest wall indicates that the abnormality is within the pleural space. Portable lateral views are insufficient in making this distinction when patients cannot be transported. Lateral decubitus portable films or ultrasonography can be performed as tolerated by the patient and can be helpful in making this diagnosis. 46 If the patient cannot be turned or positioned as required, or if the diagnosis is not obtainable at the bedside, computed tomography is an excellent modality for detecting pleural fluid, identifying loculations for subsequent treatment planning (Fig. 7), and distinguishing empyema from lung abscess. 10, 35 Despite the logistical difficulties in transporting and maintaining life support systems of ICU patients, this accurate means of diagnosis may be lifesaving. Mirvis et al3° studied 56 ICU patients who underwent computed tomography and found significant additional information beyond that available from bedside radiographs in 70% of the studies, including empyema (17% ), large pleural effusions (13% ), malpositioned or occluded thoracostomy tubes (15% ), pneumothorax requiring chest tube (10% ), and lung abscess (8% ). The radiographic manifestations of septic pulmonary emboli and infection include the presence of patchy bilateral parenchymal opacities that typically progress slowly, but occasionally progress rapidly, mimicking pulmonary edema. The source of infection may arise from the lung, urinary tract, a wound, an abscess, or an indwelling catheter. 32 Computed tomography is more sensitive than plain radiography in the detection and diagnosis of septic emboli, and may yield a diagnosis

Figure 7. Empyema. A, Posteroanterior chest radiograph demonstrates diffuse opacification of the left hemithorax with shift of the mediastinum, including the heart and tracheobronchial tree to the left, indicating mass effect, which may represent a combination of fluid or mass. B, Contiguous contrast-enhanced CT images of the left hemithorax demonstrates multiple loculated fluid collections with thick enhancing walls (white asterisks), indicating the need for either multiple percutaneous catheter drainage or surgery, and not amenable to single catheter drainage. The underlying lung (black asterisk) is collapsed by the mass effect of the fluid collections.

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before it is suspected clinically or radiographically .19 , 23 Although the classic findings of septic pulmonary emboli on plain films include peripheral wedge-shaped opacities and nodules with or without cavitation, of the 18 cases of septic pulmonary emboli on computed tomography reported by Kuhlman et al, 23 the chest radiograph was normal in three and revealed nonspecific opacities in another three. In 83% of patients in this series, there were multiple pulmonary nodules ranging in size from 0.5 to 3.5 cm on computed tomography; 50% were associated with cavitation; and 39% of patients also had pleural effusions.

ASPIRATION

Critically ill patients are predisposed to aspiration because of tracheal and esophageal intubation, depressed cough reflex, impaired mucociliary function, increased secretions, supine position, and cardiopulmonary resuscitation events. Many episodes of aspiration occur during the night, often unrecognized by caretakers. The diagnosis should be considered when portable radiographs demonstrate the sudden appearance of new focal pulmonary opacities. In 1975, Bartlett and Gorbach6 differentiated three types of aspiration based on the type of fluid aspirated and subsequent lung injury and reaction-toxic, bland, and infectious. The aspiration of toxic acidic gastric contents with a pH of less than 2.5 or water-soluble contrast material results in severe bronchospasm and chemical pneumonitis within minutes. Fifty percent of these patients subsequently develop fever and leukocytosis. When massive, there may be immediate apnea, hypotension, and shock. The radiographs and clinical picture may mimic pneumonia, but both gradually improve over a period of 1 to 2 days, unlike pneumonia. When water, blood, or other bland fluid is aspirated, the radiograph often is normal unless a large volume of fluid is aspirated. The associated transient respiratory distress improves after suctioning and there is no significant inflammatory lung response. When toxic contents or bland fluid are aspirated in conjunction with solid foreign material such as food, the clinical and radiographic picture is one of airway obstruction with distal atelectasis and frequently subsequent pneumonia. The aspiration of infected material, including pharyngeal/airway secretions colonized by multiple organisms, results in gravity-dependent radiographic findings of pneumonia. 24 These are persistent regions of airspace consolidation that occur frequently in the superior segments of the lower lobes or the posterior segments of the upper and lower lobes when the patient has been in a supine position (Fig. 8). If the patient had been prone, as in a rotobed, the abnormality may be located in the anterior segments of the upper and lower lobes, the middle lobe, or the lingula. Patients aspirating while in a decubitus position may involve multiple or even all segments of one lung while sparing the other.

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Figure 8. Aspiration. Patchy bilateral airspace opacity, predominantly in the lower lobes, with an air-fluid level in the esophagus (arrows) .

ADULT RESPIRATORY DISTRESS SYNDROME

Although the diagnosis of ARDS is based primarily on clinical findings, the chest radiograph may provide significant additional diagnostic information and certainly provides important supplemental information concerning the effectiveness of treatment and ultimate prognosis of the patient. In 1977, Bachofen and Weibel5 described the three pathologic phases of ARDS lung injury and response. The acute phase, represented pathologically by diffuse endothelial cell injury with alveolar capillary leak of large protein molecule fluid and neutrophils, manifests as diffuse, ill-defined alveolar opacities localized predominantly in the peripheral portions of the lungs. 14 As capillary leak progresses, with larger protein molecules escaping, increased amounts of fluid extravasate from the intravascular space into the alveoli, causing widespread pulmonary opacification and, in certain cases, complete "white-out" of the lungs. 18 With injury to alveolar epithelial cells, there is decreased surfactant production and decreased lung compliance. This is reflected by the radiographic findings of relatively small lung volume and atelectasis. 14 In contrast to cardiogenic, uremic, and hypervolemic pulmonary edema, the alveolar edema of ARDS is not associated with widening of the vascular pedicle, cardiomegaly, or altered pulmonary blood flow distribution. When the pulmonary vessels can be distinguished, they often are constricted. Because capillary leak occurs directly into the alveolar spaces, septal lines usually are absent. In the subacute phase, occurring over the next 5 to 10 days, the pathologic finding of proliferation of epithelial cells and fibroblasts, as well as collagen deposition, produces the radiograpnic findings of progressive lung destruction and a transition from alveolar to interstitial opacities. Findings of barotrauma, including pneumothorax and pneumatocele formation, are common (Fig. 9). 1 ' 26 The patient eventually may enter the

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Figure 9. Adult respiratory distress syndrome (ARDS) with barotrauma. A, Diffuse bilateral airspace disease with air-bronchograms unchanged over 7 days following abdominal surgery complicated by bowel perforation and abscess formation. ARDS complicated by pneumatocele in right lung (asterisk) and bilateral pneumothoraces (arrowheads). B, Contiguous CT images over 7 days again demonstrate diffuse airspace (ground glass) opacity of ARDS and the large right pneumatocele (asterisk), but also reveals that the pneumothoraces are loculated posteriorly and medially (black arrowheads) and therefore not drained by indwelling thoracostomy tubes, multiple additional pneumatoceles (arrows), and an anterior pneumothorax (open arrow).

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chronic phase, which occurs several weeks after the initial lung injury, and wherein fibrosis and focal emphysema are the radiographic hallmarks.

SUMMARY

Timely performance and accurate interpretation of portable chest radiographs in the ICU setting are fundamental components of quality care. Teamwork between intensive care clinicians and radiologists is necessary to assure that the appropriate studies, of high technical quality, are obtained. By working together to integrate available clinical information with systematic comprehensive analysis of images, accurate diagnoses can be made, optimal treatment instituted, and successful outcomes optimized. ACKNOWLEDGMENT The authors wish to thank Cynthia Sims Holmes for her expertise and assistance in the preparation of the manuscript.

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2. Anderson HL III, Delius RE, Sinard JM, et al: Early experience with adult extracorporeal membrane oxygenation in the modern era. Ann Thorac Surg 53:553-563, 1992 3. Andrews CP, Coalson JJ, Smith JD, et al: Diagnosis of nosocomial bacterial pneumonia in acute diffuse lung disease. Chest 80:254-258, 1981 4. Andrews JC, Marx VM, Williams DM, et al: The upper arm approach for placement of peripherally inserted central catheters for protracted venous access. AJR 158:427-429, 1992 5. Bachofen M, Weibel ER: Alterations of the gas exchange apparatus in adult respiratory insufficiency associated with septicemia. Am Rev Respir Dis 116:589-615, 1977 6. Bartlett JG, Gorbach SL: The triple threat of aspiration pneumonia. Chest 68:560-566, 1975 7. Bekemeyer WB, Crapo RO, Calhoon S, et al: Efficacy of chest radiography in a respiratory intensive care unit: A prospective study. Chest 88(5):691-696, 1985 8. Benjamin JJ, Cascade PN, Rubenfire M, et al: Left lower lobe atelectasis and consolidation following cardiac surgery: The effect of topical cooling on the phrenic nerve. Radiology 142:11-14, 1982 9. Bitetti J, Zimmerman JE: A clinician's perspective of critical care imaging. In Goodman LR, Putman CE (eds): Critical Care Imaging, ed 3. Philadelphia, WB Saunders, 1992, p 29 10. Bressler EL, Francis IR, Glazer GM, et al: Bolus contrast medium enhancement for distinguishing pleural from parenchymal lung disease: CT features. JCAT 11:436-440, 1987 11. Cantwell KG, Press HC JR, Anderson JE: Beas!de raaiographic examinations: Indications and contraindications. Radiology 129:383-384, 1978 12. Cascade PN, Kantrowitz A, Wajszczuk WJ, et al: The chest x-ray in acute left ventricular power failure: An aid to determining prognosis of patients supported by intraaortic balloon pumping. Am J Roentgenol 126:1147- 1154, 1976

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13. Goodman LR, Almassi GH, Troup PJ, et al: Complications of automatic implantable cardioverter defibrillators: Radiographic, CT, and echocardiographic evaluation. Radiology 170:447--452, 1989 14. Greene R: Adult respiratory distress syndrome: Acute alveolar damage. Radiology 163:57-66, 1987 15. Harris RS: The importance of proximal and distal air bronchograms in the management of atelectasis. Can Assoc Radial J 36:103-109, 1985 16. Henschke CI, Pasternack GS, Schroeder S, et al: Bedside chest radiography: Diagnostic efficacy. Radiology 149:23-26, 1983 17. Herman PG, Khan A, Kallman CE, et al: Limited correlation of left ventricular enddiastolic pressure with radiographic assessment of pulmonary hemodynamics. Radiology 174:721-724, 1990 18. Holter JF, Weiland JE, Pach ER, et al: Protein permeability in adult respiratory distress syndromes. J Clin Invest 78:1513-1522, 1986 19. Huang RM, Naidich DP, Lubat E, et al: Septic pulmonary emboli: CT-radiographic correlation. AJR 153:41--45, 1989 20. Janower ML, Jennas-Nocera Z, Mukai J: Utility and efficacy of portable chest radiographs. AJR 142:265-267, 1984 21. Jurmann MJ, Demertzis S, Schaffers HJ, et al: Intravascular oxygenation for advanced respiratory failure. ASAIO J 38:120-124, 1992 22. Kostuk W, Barr JW, Simon AL, et al: Correlations between the chest film and hemodynamics in acute myocardial infarction. Radiology 47:623-632, 1973 23. Kuhlman JE, Fishman EK, Teigen C: Pulmonary septic emboli: Diagnosis with CT. Radiology 174:211-213, 1990 24. Landay MJ, Christensen EE, Bynum LJ: Pulmonary manifestations of acute aspiration of gastric contents. AJR 131:587-592, 1978 25. McHugh TJ, Forrester JS, Adler L, et al: Pulmonary vascular congestion in acute myocardial infarction: Hemodynamic and radiologic correlations. Ann Intern Med 76:29-33, 1972 26. McLoud TC, Barash PG, Ravin CE: PEEP: Radiographic features and associated complications. AJR 129:209-213, 1977 27. Milne ENC: A physiological approach to reading critical care unit films. J Thorac Imaging 1(3):60-90, 1986 28. Milne ENC: Physiological interpretation of the plain radiograph in mitral stenosis, including a review of criteria for the radiological estimation of pulmonary arterial and venous pressures. Br J Radial 36:902-913, 1963 29. Milne ENC, Pistolesi M, Miniati M, et al: The vascular pedicle of the heart and the vena azygos: Part I: The normal subject. Radiology 152:1-8, 1984 30. Mirvis SE, Tobin KD, Kostrubiak I, et al: Thoracic CT in detecting occult disease in critically ill patients. AJR 148:685-689, 1987 31. Mock CN, Burchard KW, Hasan F, et al: Surgical intensive care unit pneumonia. Surgery 104:494--499, 1988 32. Norwood SH, Civetta JM: Evaluating sepsis in critically ill patients. Chest 91:137-144, 1987 33. Pham DH, Huang D, Korwan A, et al: Acute unilateral pulmonary non-ventilation due to mucous plugs. Radiology 165:135-137, 1987 34. Pistolesi M, Miniati M, Milne ENC, et al: The chest roentgenogram in pulmonary edema. Clin Chest Med 6(3):315-344, 1985 35. Pugatch RD, Paling LJ, Robbins AH, et al: Differentiation of pleural and pulmonary lesions using computed tomography. J Comput Asist Tomogr 2:601-606, 1978 36. Roberts J, Barnes W, Pennoch MHS, et al: Diagnostic accuracy of fever as a measure of postoperative pulmonary complications. Heart Lung 17:166--170, 1988 37. Rose CP, Stolberg HO: The limited utility of the plain chest film in the assessment of left ventricular structure and function. Invest Radio! 17:139-144, 1982 38. Shevland JE, Hirleman MT, Hoang KA, et al: Lobar collapse in the surgical intensive care unit. Br J Radial 56:531-534, 1983 39. Silverman SG, Mueller PR, Saini S, et al: Thoracic empyema: Management with image-guided catheter drainage. Radiology 169:5-9, 1988 40. Simon M: The pulmonary vessels: Their hemodynamic evaluation using routine radiographs. Radial Clin North Am 2:363-375, 1963

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lracheobronchial

45.

Ll6.

47.

consolidation of the left lower lobe: A

1988 Address reprint request-s to

MD Center 2910 1500 East l.\1edica1 Center Drive Ann Arbor, rvlI 48109-0326