the role of imaging in acute respiratory distress syndrome

Critical Care Radiology: The Role of Imaging in Acute Respiratory Distress

SyndromeAndrew Chalupka, MS III

Gillian Lieberman, MD

September, 2011

Andrew Chalupka, MS IIIGillian Lieberman, MD

Overview• Case presentation: index patient• Use of chest radiography to distinguish between causes of airspace

opacification

• Use of chest radiography to distinguish between cardiogenic

and non‐

cardiogenic

pulmonary edema• Acute Respiratory Distress Syndrome (ARDS):

– Definition– Associated disorders– Diagnostic criteria– Pathophysiology

• Imaging choices for ARDS• Radiologic findings in ARDS by stage• Implications of imaging for understanding ARDS pathophysiology• Implications of imaging for managing ARDS

2


Index Patient: Brief History

• 33 year‐old man

• Two‐day history of “feeling unwell”• Day of admission: onset of “worst headache

of [his] life,”

followed by nausea and vomiting

• At outside hospital, CT showed extensive subarachnoid hemorrhage and

intraventricular

hemorrhage

3


Index Patient: Brief Hospital Course

• Within an hour of arrival in the ED, becomes lethargic and is intubated

• Admitted to ICU• Week 1: Tachycardia, hypertension, and fever

– Therapeutic hypothermia protocol initiated

• Week 2: Pneumonia• Week 3: Extubated

dyspnea, rapid hypoxemia re‐intubated

4


Index Patient

The patient’s chest radiograph follows.

It was taken 24 hours after the onset of his dyspnea

and hypoxemia.

Attempt to interpret the film independently,

then continue to view findings.

5

6Source: Beth Israel Deaconess

Medical Center PACS

Index Patient: Chest radiograph,24 hours after onset of respiratory distress


Medical Center PACS

Diffuse,

hazy

opacities

Index Patient: Chest radiograph


Medical Center PACS

Diffuse,

hazy

opacities



Medical Center PACS

Air bronchograms



Medical Center PACS

Diffuse,

hazy

opacities

Diffuse,

hazy

opacities

Air

bronchogram

s



Given only a chest radiograph with an airspace/alveolar

pattern of opacification, what can we determine about its

etiology?

Quite a bit.

11


Airspace OpacificationCause of Opacification Radiographic AppearanceCardiogenic pulmonary edema • Diffuse

• Symmetric• Perihilar• ±

Dependent

Non‐cardiogenic pulmonary edema(e.g., ARDS)

• Patchy• Asymmetric• Peripheral• ±

Dependent• ± Air bronchograms

Bronchopneumonia • Patchy• Asymmetric• Peripheral• Non‐dependent

Aspiration pneumonia • Patchy• Asymmetric• Dependent

Septic infarcts • Peripheral• Wedge‐shaped

12Adapted from: Trotman‐Dickenson B. Radiography for the Critical Care Patient. In: McLoud TC, Boiselle

PM, eds.

Thoracic Radiology: the Requisites. Philadelphia, PA: Mosby; 2010: 136‐159.


Our patient’s film showed airspace opacification that was diffuse, peripheral,

and worse at the bases (i.e., potentially dependent) with air bronchograms.

It demonstrates many, but not all, of the

common radiographic features of non‐cardiogenic pulmonary edema.

13


Pulmonary Edema

• Abnormal accumulation of fluid in the extravascular compartments of the lung

• Net fluid movement = Kf

([Pc

– Pi

] –

σ[πc

–

πi

])

• Pathophysiologic categories of pulmonary edema:– increased hydrostatic pressure edema

– permeability edema with diffuse alveolar damage (DAD)

– permeability edema without DAD

– mixed edema

14Source: Ketai LH, Godwin JD. A new view of pulmonary edema and acute respiratory distress

syndrome. J Thorac Imaging. 1998;13(3):147‐71.


Having narrowed down the cause of our patient’s airspace opacification to

pulmonary edema, we can use the features of his chest radiograph to determine the type

of pulmonary edema.

The chest radiograph is a powerful tool in

the critical care setting; it can provide an assessment of volume status and vascular flow patterns.

15


Radiographic Features of Pulmonary Edema: Cardiac vs. Non‐cardiac

Signs Cardiogenic Edema Fluid Overload ARDS

Cardiomegaly + +

Vascular redistribution +

Widened vascular pedicle + +

Pleural effusions + +

Kerley lines + +

Peribronchial cuffing + +

Airspace opacification Diffuse perihilar Central

perihilar

Patchy

peripheral

16Adapted from: Trotman‐Dickenson B. Radiography for the Critical Care Patient. In: McLoud TC, Boiselle

PM, eds.



Based on our patient’s clinical presentation, the airspace opacification pattern on his

chest radiograph, and the absence of CXR features seen in cardiogenic or fluid‐

overload pulmonary edema, we suspect that he has Acute Respiratory Distress

Syndrome (ARDS).

Let’s continue by briefly examining the etiology and pathophysiology of ARDS.

17


ARDS: Definition and Associated Disorders• A clinical syndrome of abrupt‐onset dyspnea and

hypoxemia in the setting of diffuse pulmonary infiltrates• Disorders associated with ARDS:

18

Direct lung injury Indirect lung injury

Pneumonia Sepsis

Aspiration of gastric contents Shock

Pulmonary contusion Severe trauma

Drowning Multiple transfusions

Fat/amniotic fluid embolism Salicylate or narcotic overdose

Smoke/toxic gas inhalation Pancreatitis

Sources:Levy BD, Shapiro SD. Acute Respiratory Distress Syndrome. In: Fauci AS, Braunwald E, Kasper DL, Hauser SL, Longo DL,

Jameson JL, Loscalzo J, eds. Harrison's Principles of Internal Medicine

17e. New York, NY: McGraw Hill; 2008: 1680‐1684.Wheeler AP, Bernard GR. Acute lung injury and the acute respiratory distress syndrome: a clinical review. Lancet.

2007;369(9572):1553‐64.


ARDS: Diagnostic Criteria1.

Acute onset (<7 days)

2.

PaO2

/FIO2

<200 mmHg• Acute Lung Injury: PaO2

/FIO2

<300 mmHg

3.

Diffuse, bilateral pulmonary infiltrates on frontal radiograph

4.

Absence of left atrial hypertension• PCWP <18 mmHg if measured, or• No clinical evidence of elevated LA pressure

19

Sources:Levy BD, Shapiro SD. Acute Respiratory Distress Syndrome. In: Fauci AS, Braunwald E, Kasper DL, Hauser SL, Longo DL,

Jameson JL, Loscalzo J, eds. Harrison's Principles of Internal Medicine

17e. New York, NY: McGraw Hill; 2008: 1680‐1684.Wheeler AP, Bernard GR. Acute lung injury and the acute respiratory distress syndrome: a clinical review. Lancet.

2007;369(9572):1553‐64.


ARDS: Pathophysiology• Alveolar capillary membrane: 2 separate barriers

– Vascular endothelium– Alveolar epithelium (type I pneumocyte)

• ARDS: Injury to, and compromise of, either barrier

– Increased vascular permeability• Alveolar flooding (exudative/protein‐rich)

– Hyaline membrane formation• Loss of diffusion capacity• Damage to type II pneumocytes widespread surfactant

abnormalities

20Source: Husain AN. The Lung. In: Kumar V, Abbas AK, Fausto N, Aster JC, eds. Robbins and Cotran Pathologic Basis of

Disease 8e. Philadelphia, PA: Saunders; 2010: 677‐737.


Imaging Choices in ARDS• Chest radiograph

– To support a diagnosis of ALI/ARDS in patients fulfilling clinical

criteria– To detect or confirm a suspected subclinical complication (e.g.,

nosocomial pneumonia)

– To monitor progression or regression of prior findings• CT

– To quantify the extent of lung abnormality in patients with

equivocal CXR

– To determine the etiology of the ARDS– To identify areas of dependent, dense, parenchymal

opacification (compression atelectasis)

21

Sources:Desai SR. Acute respiratory distress syndrome: imaging of the injured lung. Clin Radiol. 2002;57(1):8‐17.Desai SR, Wells AU, Suntharalingam G, Rubens MB, Evans TW, Hansell DM. Acute respiratory distress syndrome

caused by pulmonary and extrapulmonary injury: a comparative CT study. Radiology. 2001;218(3):689‐93.


Stages of ARDS

• ARDS is comprised of three stages, each of which demonstrates distinct radiographic

findings.1.

Exudative Stage

2.

Proliferative Stage

3.

Fibrotic Stage

22


Stages of ARDS: Exudative Stage

• Pathophysiologic: – Interstitial edema, rapidly progressing to the

filling/flooding of alveolar spaces with an exudate– Hyaline membrane formation

• Radiologic (plain film):– First 24 hours: normal CXR– Early: interstitial edema (perihilar)– Later: alveolar consolidation (peripheral); air

bronchograms

23

Sources: Gluecker T, Capasso P, Schnyder P, Gudinchet F, Schaller MD, Revelly JP, Chiolero R, Vock P, Wicky S. Clinical and

radiologic features of pulmonary edema. Radiographics. 1999;19(6):1507‐31.Desai SR. Acute respiratory distress syndrome: imaging of the injured lung. Clin Radiol. 2002;57(1):8‐17.


Medical Center PACS

Companion Patient 1:Early

exudative stage

Chest radiograph


Medical Center PACS

Perihilar,

interstitial

opacities

Companion Patient 1:Early

exudative stage

Chest radiograph


Medical Center PACS

Index Patient:Later

exudative stage

Chest radiograph


Medical Center PACS

Index Patient:Later

exudative stage

Chest radiograph

Peripheral,

alveolar

consolidation


Stages of ARDS: Exudative Stage

• CT findings: Gravitational gradient– Ventral‐dorsal

• Anterior: normal lung• Posterior: dense consolidation• In between: ground‐glass opacification

– Cephalocaudal• Increasing abnormal density caudally

• CT findings: Airway changes– Bronchial dilatation

28


radiologic features of pulmonary edema. Radiographics. 1999;19(6):1507‐31.Desai SR. Acute respiratory distress syndrome: imaging of the injured lung. Clin Radiol. 2002;57(1):8‐17.


Medical Center PACS

Companion Patient 2:Later exudative stage

CT, axialImage 1


Medical Center PACS


CT, axialImage 1

Normal lung


Medical Center PACS


CT, axialImage 1

Ground‐glass

opacities


Medical Center PACS


CT, axialImage 1

Dense

consolidation


Medical Center PACS


CT, axialImage 1

Normal lung

Ground‐glass

opacities

Dense

consolidation


Medical Center PACS


CT, axialImage 1


Medical Center PACS


CT, axialImage 2


Medical Center PACS


CT, axialImage 3


Medical Center PACS


CT, axialImage 1


Medical Center PACS


CT, axialImage 1

Normal

lung


Medical Center PACS


CT, axialImage 1

Ground‐glass

opacities


Medical Center PACS


CT, axialImage 1

Dense

consolidation


Medical Center PACS


CT, axialImage 1

Dense

consolidation

Ground‐glass

opacities

Normal

lung


Medical Center PACS


CT, axialImage 1


Medical Center PACS


CT, axialImage 2


Medical Center PACS


CT, axialImage 3


Medical Center PACS


CT, axialImage 4


Medical Center PACS


CT, axialImage 5


Medical Center PACS


CT, axialImage 6


Stages of ARDS: Proliferative Phase

• Pathophysiologic:– Organization of fibrinous exudate– Regeneration of alveolar lining

• Radiologic:– Inhomogeneous areas of ground‐glass opacity

– Thickening of alveolar septae

48Source: Gluecker T, Capasso P, Schnyder P, Gudinchet F, Schaller

MD, Revelly JP, Chiolero R, Vock P, Wicky S. Clinical and

radiologic features of pulmonary edema. Radiographics. 1999;19(6):1507‐31.


Stages of ARDS: Fibrotic Stage

• Pathophysiologic: – Scarring/fibrosis– Formation of subpleural and intrapulmonary cysts

• Radiologic:– Distortion of interstitial and bronchovascular markings

– Cystic lesions– Complications of cysts or barotrauma:

• Aberrant air: pneumothorax, pneumatocele

49


radiologic features of pulmonary edema. Radiographics. 1999;19(6):1507‐31.Goodman LR. Congestive heart failure and adult respiratory distress syndrome. New insights using computed

tomography. Radiol Clin North Am. 1996 Jan;34(1):33‐46.


Implications of Imaging for Understanding ARDS

• CT allows quantitative analysis of volumes of gas and tissue• CT data of the whole lung have changed our understanding

of the pathophysiology of ARDS– Lung volume = tissue volume + gas volume– We now understand that there is a marked

reduction

in overall

lung volume

at the expense of the volume of the lower lobes

• Increase in tissue in upper lobes (edema, inflammation)• Loss of aeration of lower lobes (compression by heart, abdominal

contents)

• Old understanding of ARDS: overall volume of lung preserved

because gain of tissue was expected to exceed loss of gas

• New understanding of ARDS: reduction

in overall lung volume

because loss of gas is greater than gain of tissue

– Loss of aeration differs between patients50Source: Rouby JJ, Puybasset L, Nieszkowska A, Lu Q. Acute respiratory distress syndrome: lessons from computed

tomography of the whole lung. Crit Care Med. 2003;31(4 Suppl):S285‐95.


Lower‐lobe predominant pattern

• 40% of patients

• Loss of aeration:

– Mainly in lower lobes

– Minimal involvement of

upper lobes

• Mortality: 40%

51

CT scan from a 74‐year‐old patient with

ARDS caused by severe bronchopneumonia

•Upper lobes: some parts remain normally

aerated (black)•Lower lobes: either poorly aerated (gray) or

nonaerated (red).

Image: Rouby JJ, Puybasset L, Nieszkowska A, Lu Q. Acute respiratory

distress syndrome: lessons from computed tomography of the whole

lung. Crit Care Med. 2003;31(4 Suppl):S285‐95.


Lower‐lobe exclusive pattern

• One‐third of patients


– Exclusively in lower lobes

• Mortality: 40%

52

CT scan from 50‐yr‐old patient with ARDS

caused by aspiration pneumonia

•Upper lobes: normally aerated (black).•Lower lobes: either poorly aerated (gray) or

nonaerated (red).

Image: Rouby JJ, Puybasset L, Nieszkowska A, Lu Q. Acute respiratory

distress syndrome: lessons from computed tomography of the whole

lung. Crit Care Med. 2003;31(4 Suppl):S285‐95.


Diffuse pattern• 25% of patients


– Massive

– Equally‐distributed throughout lung

• Mortality: 70%

53

CT scan from in a 53‐year‐old patient with

ARDS caused by Pneumocystis

jirovecii

•Entire lung: nonaerated

(red) or poorly

aerated (gray).

Image: Rouby

JJ, Puybasset

L, Nieszkowska

A, Lu Q. Acute respiratory distress syndrome: lessons from computed tomography of

the whole lung. Crit

Care Med. 2003;31(4 Suppl):S285‐95.


Implications of Imaging for ARDS Management

• CT has led to safer and more‐effective management of ARDS

– Understanding that overall lung volume and cephalocaudal

lung dimensions are reduced at the

expense of the lower lobes• Prone and semi‐recumbent positioning of patients

– Assessment of alveolar recruitment and detection of lung overinflation

• Optimization of PEEP: maximizing recruitment while

limiting barotrauma

54Source: Rouby

JJ, Puybasset

L, Nieszkowska

A, Lu Q. Acute respiratory distress syndrome: lessons from computed

tomography of the whole lung. Crit

Care Med. 2003;31(4 Suppl):S285‐95.


Summary• The different causes of airspace opacification

on plain film have distinctive

radiographic appearances.

• Pulmonary edema is one such cause. It is possible to deduce the

origin of

pulmonary edema (cardiac, fluid overload, or ARDS) based on the

radiographic features of a chest film.

• ARDS is a clinical syndrome of severe dyspnea

of rapid onset and

hypoxemia in the setting of diffuse pulmonary infiltrates.

• ARDS is caused by diffuse lung injury that leads to leakage of alveolar

capillaries, allowing flooding of alveolar spaces with an exudate.

• The menu of imaging for ARDS includes plain film and CT.• ARDS has three phases (exudative, proliferative, and fibrotic), each of

which has distinct radiographic features.

• CT has changed our understanding of the pathophysiology of ARDS.• CT has changed our approach to the management of ARDS.

55


References• Desai SR. Acute respiratory distress syndrome: imaging of the injured lung. Clin

Radiol.

2002;57(1):8‐17.

• Desai SR, Wells AU, Suntharalingam

G, Rubens MB, Evans TW, Hansell

DM. Acute respiratory

distress syndrome caused by pulmonary and extrapulmonary

injury: a comparative CT study.

Radiology. 2001;218(3):689‐93.

• Gluecker

T, Capasso

P, Schnyder

P, Gudinchet

F, Schaller MD, Revelly

JP, Chiolero

R, Vock

P, Wicky

S. Clinical and radiologic features of pulmonary edema. Radiographics. 1999;19(6):1507‐31.

• Goodman LR. Congestive heart failure and adult respiratory distress syndrome. New insights using

computed tomography. Radiol

Clin

North Am. 1996 Jan;34(1):33‐46.• Husain AN. The Lung. In: Kumar V, Abbas

AK, Fausto

N, Aster JC, eds. Robbins and Cotran

Pathologic Basis of Disease 8e. Philadelphia, PA: Saunders; 2010: 677‐737.

• Ketai

LH, Godwin JD. A new view of pulmonary edema and acute respiratory distress syndrome. J

Thorac

Imaging. 1998;13(3):147‐71.• Levy BD, Shapiro SD. Acute Respiratory Distress Syndrome. In: Fauci

AS, Braunwald

E, Kasper DL,

Hauser SL, Longo DL, Jameson JL, Loscalzo

J, eds. Harrison's Principles of Internal Medicine

17e.

New York, NY: McGraw Hill; 2008: 1680‐1684.

• Rouby

JJ, Puybasset

L, Nieszkowska

A, Lu Q. Acute respiratory distress syndrome: lessons from

computed tomography of the whole lung. Crit

Care Med. 2003;31(4 Suppl):S285‐95.• Trotman‐Dickenson B. Radiography for the Critical Care Patient. In: McLoud

TC, Boiselle

PM, eds.


• Wheeler AP, Bernard GR. Acute lung injury and the acute respiratory distress syndrome: a clinical

review. Lancet. 2007;369(9572):1553‐64.

56


Acknowledgements

• The following individuals provided invaluable assistance in acquiring and interpreting

images:– Javier Perez‐Rodriguez, M.D.– Alexander Bankier, M.D.– Diana Litmanovich, M.D.– Paul Sprin, M.D.

• Thanks also to Emily Hanson for her logistical assistance.

57

the role of imaging in acute respiratory distress syndrome

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