PATHOPHYSIOLOGY OF
ACUTE RESPIRATORY
DISTRESS SYNDROME
DR.R.MYTHILI MD.,SR
DEPARTMENT OF PATHOLOGY
KALLAKURICHI MEDICAL COLLEGE

OVERVIEW
INTRODUCTION
ETIOLOGY
PATHOGENESIS
INVESTIGATION
ROLE OF PATHOLOGICAL DIAGNOSIS IN ARDS
MORPHOLOGY AND HISTOPATHOLOGY

INTRODUCTION
Acute Respiratory distress syndrome(ARDS)
defined by
◦ American and European Consensus Conference
(1994)
◦ Acute onset
◦ Bilateral pulmonary infiltrates on CXR/ CT
◦ Impaired oxygenation
◦ Absence of left atrial hypertension

Cont……
PaO2 / FiO2 (normal range 300 - 500 mmHg)
◦ Ratio of <300mmHg >200 mmHg – Mild ARDS
◦ Ratio of <200mmHg >100 mmHg – Moderate ARDS
◦ Ratio of <100mmHg – Severe ARDS

Cont…..
In Pathology
◦‘Acute lung injury’ by Katzenstein’
◦Inflammatory / fibroblastic
processes
◦Acute onset
◦Loose edematous ‘granulation
tissue’ like stroma
◦Reflecting response to insult
occurring at one point of time.
HPE

ETIOLOGY
DIRECT PULMONARY INSULT
Pneumonia
Aspiration
Oxygen toxicity
Near drowning
Smoke
INDIRECT PULMONARY INSULT
Sepsis
DIC
TRALI
Pancreatitis
Uremia

PATHOPHYSIOLOGY OF ARDS

CONT…
Exudative
phase
• Endothelial activation
• Neutrophil recruitment and
Macrophage activation
• Alveolar epithelial injury
• Edema
Proliferative
phase
• Organisation of exudate
• Migration of fibroblasts
• Fibroblast and type 2 pneumocyte proliferation
Fibrotic
phase/
Resolution
• Fibrosis
• Resolution

INVESTIGATION
Routine blood investigation
ABG
Blood / sputum culture
CXR
HRCT chest
ECG , ECHO
Other Investigations (as indicated)

Role Of Pathological Dx In ARDS
ARDS - essentially clinical diagnosis
Most common specimens:
BAL fluid - Infective organisms
- Cytopathology
- Regenerating alveolar epithelial cells - severe reactive
cytological atypia,
- Avoid erroneous diagnosis of malignancy.

Cont…..
Lung biopsy - clinical uncertainty around diagnosis,

Morphology & HPE
Exudative phase
Gross Microscopy

Morphology & HPE
Proliferative phase
Gross Microscopy
Proliferative phase

Morphology & Microscopy
Fibrosis
Gross Microscopy

TAKE HOME MESSAGES
◦ ARDS defined as acute onset of impair oxygenation,Bilateral
pulmonary infiltrates on CXR/ CT and absence of any cardiogenic
causes.
◦ Based on PaO2/FiO2 ratio, ARDS divided into mild, moderate,
severe degree of ARDS
◦ Based on pathology it has three phases
◦ Exudative phase
◦ Proliferative phase
◦ Resolution/ Fibrotic phase

REFERENCE
ROBBINS AND COTRAN PATHOLOGY 10TH EDITION
HARRISION’S PRINCIPLES OF INTERNAL MEDICINE
KATZENSTEIN AND ASKIN’S SURGICAL PATHOLOGY OF
NONNEOPLASTIC LUNG DISEASE,4TH EDN. PLILADELPHIA,PA: WB
SAUNDERS,2006:17-50
WALLACE WAH, SIMPSONAJ, HIRANI N.ACUTE LUNG INJURY.IN:
HASLETONP, FLIEDER DB(EDS),SPENCER’S PATHOLOGY OF THE
LUNG,6TH EDN.CAMBRIDGE UNIVERSITY PRESS

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