ARDS

Question 1

Describe the types of cells found in the alveolus

Answer 1

Type 1: gas exchange (95% of SA; 40% of total cells)

Type 2: secrete surfactant; critical for healing/repair

Question 2

Describe the histological characteristics of ARDS

Answer 2

Diffuse alveolar damage (DAD)

• damages alveolar & capillary endothelium
• hyaline membrane around alveoli
• interstitial edema (inflam infiltrate)
• fibroblast proliferation
• connective tissue deposition

Question 3

Describe the etiology of ARDS

Answer 3

(Usually a combination of factors)
Direct Injuries:
 - *diffuse pulm infections*
 - inhaled irritants
 - *gastric irritation*
Systemic conditions:
 - *septic shock*
 - *trauma*
 - near-drowning

Question 4

Describe the pathogenesis of ARDS

Answer 4

ENDOTOXIN

• -> release of TNF-alpha (from macrophages & monocytes)
• -> up-regulates adhesion molecules on endothelial cells
• -> release of cytokines
• -> activates complement and C5a
• -> up-regulates adhesion molecules on neutrophils
• -> neutrophils stick to endothelium
• -> neutrophils sequester in lung capillaries

NEUTROPHILS

• -> release O2 radicals, PGs, LTs, proteases
• -> damage endothelium –> permeable –> coagulation
• -> Necrosis & Epithelial/Endothelial Damage

Question 5

Define pneumonia

Answer 5

Inflammation of pulmonary parenchyma

• usually infectious
• often a/w consolidation of lung

Question 6

Describe the classification of pneumonia

Answer 6

Types of Classification:

• Anatomical
• Clinical
• Etiology

Question 7

What are some common causes of pneumonia?

Answer 7

Infectious:
- Bacterial (Strep pneumo, SA, H. influenzae, Klebsiella, Legionella, Moraxella cararhallis, Pseudomonas)
- Viral (influenza, CMV)
- Fungal (histoplasma, coccidiodes, cryptococcus)
- PCP
Idiopathic

Question 8

What are some predisposing causes of pneumonia

Answer 8

• Suppression of cough reflex
• Immunocompromised
• Impaired cilia fxn
• Impaired dust cell fxn
• Pulm edema
• Hospitalization

Question 9

Describe Lobar Pneumonia

Answer 9

• uniform consolidation
• part of or entire lobe
• most common type of CAP
• usually due to Strep pneumo

Question 10

Describe the complications of pneumonia

Answer 10

• Bacterial dissemination
• Lung abscess formation
• Empyema
• Death

Question 11

Describe the pathology of TB

Answer 11

• Caseating necrosis (macroscopic)

- Inflammatory granulomatous necrosis (microscopic)

Question 12

Describe the causes of pneumonia in a compromised host

Answer 12

• Usual bacterial pathogens
• Mycobacterium infections
• fungal
• PCP
• CMV

Question 13

What are the characteristics of ARDS?

Answer 13

Respiratory Insufficiency

• Rapid onset
• Life-threatening
• may progress to other organ failure

Question 14

Pathological stages of Lobar Pneumonia

Answer 14

1: congestion (intra-alveolar fluid)
2: red hepatization (neutrophils + RBCs + fibrin in alveoli)
3: gray hepatization (macrophages ingest debris)
4: resolution

Question 15

Describe Bronchopneumonia

Answer 15

• patchy infective consolidation
• predominantly lobar distribution
• usually bilateral
• common in hospitalized pts
• may develop from bronchitis spread to bronchiolitis

Question 16

What is the most common cause of lung abscess formations?

What are the most commonly associated pathogens?

Answer 16

Aspiration

Pathogens: anaerobes of oropharynx; SA