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ADULT RESPIRATORY DISTRESS SYNDROME (ARDS) AND CHRONIC INTERSTITIAL DISEASES

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I. ADULT RESPIRATORY DISTRESS SYNDROME
II. CHRONIC INTERSTITIAL LUNG DISEASE

QUESTIONS TO CONSIDER AS LEARNING OBJECTIVES:

The Vietnam conflict highlighted this war-related etiology of ARDS.
This component of the compliment system is the first to be triggered in ARDS.
This cellular event is the second step in the pathogenesis of ARDS.
These toxic substances are produced by neutrophils and are felt to induce vascular and epithelial damage with permeability and resultant edema.
While many pulmonary diseases may produce "white-out" on the chest X-ray, ARDS can be distinguished by this aspect of its presentation.
A hallmark of ARDS pathologically are these glassy pink membranes that line the insides of alveoli.
The mortality rate for ARDS may be as high as this figure.
The chest X-ray in ARDS can be described best by this term.
Some therapies may inherently aggravate ARDS which is what makes this manifestation of ARDS, the most difficult to manage.
The stiff lungs of ARDS are produced initially by these two related events.

CHRONIC INTERSTITIAL LUNG DISEASES: QUESTIONS TO CONSIDER AS LEARNING OBJECTIVES:

The clinical course of patients with chronic interstitial lung disease usually begins in this way.
This chest symptom is a hallmark of chronic interstitial lung disease.
This systemic therapy for patients with chronic interstitial lung disease may slow progression but rarely cures these diseases.
These particular mechanisms of organ injury were first defined in the heart in patients exposed to streptococcus bacteria in childhood, but are clearly at play in certain chronic interstitial lung diseases.
These systemic immunologically-mediated diseases frequently involve the joints and may have well-defined associated chronic interstitial lung disease.
The cells that comprise the "alveolitis" of idiopathic pulmonary fibrosis syndromes are of these two types primarily.
These 2 symptoms are commonly described by patients with idiopathic pulmonary fibrosis.
This clinical syndrome is actually a wastebasket for a number of chronic lung diseases that probably have diverse etiologies.
This surgical technique may be the only viable method for diagnosing the nature of chronic interstitial lung diseases while assisting in the selection of therapy and prediction of outcome.
This name is given to the appearance of the lungs at autopsy in patients with endstage chronic interstitial lung disease.

I. ADULT RESPIRATORY DISTRESS SYNDROME

ARDS is less a disease and more the end result of a variety of severe injuries that have in common the activation of the complement system.
The first well-described cause of ARDS was traumatic shock sustained after non-thoracic injury (shock lung).
ARDS is a clinical syndrome characterized by the sudden onset of severe shortness of breath, tachycardia, and profound hypoxia refractory to oxygen therapy. Some degree of pulmonary edema is present on chest X-ray.
Common causes of ARDS include: septic shock, traumatic shock, diffuse viral pneumonias, oxygen therapy toxicity, inhaled toxins and irritants, narcotic overdose, hypersensitivity reactions to organic solvents, cardiac surgery with an extracorporeal pump and aspiration pneumonitis.
The currently accepted pathogenesis of ARDS begins with the release of mediators (like complement C5a, platelet activating factor, leukotriene B4) into the blood that result in leukocyte aggregation in the lungs. Stimulated neutrophils release oxygen free radicals, lysosomal enzymes and products of arachidonic acid that damage the lung capillaries and alveolar epithelium.
Damaged endothelium of the capillaries allows fluid to leak from the blood. Further chemical damage by neutrophils destroys alveolar lining cells.
- The result is the accumulation of serum, fibrin and dead cell debris in the alveoli.
- Pink glassy membranes form on the insides of the alveoli. These pink membranes are called hyaline membranes.
Once hyaline membranes have formed, no surfactant is present in the alveoli so they tend to collapse (atelectasis). The combination of atelectasis and edema make the lung stiff and noncompliant.
Many patients with ARDS progress to a phase of the disease where healing occurs by fibrosis of the lung (organizing stage).
Most patients who develop ARDS have some other condition that brings them to the hospital. Once ARDS develops, there is a 50% mortality.
There is no effective therapy for ARDS once it has begun. Only resolving the initial injury (e.g. treating the initial sepsis) and supportive care are useful. Some patients will resolve their ARDS completely with few sequela.

II. CHRONIC INTERSTITIAL LUNG DISEASE

There are two main categories of chronic interstitial inflammatory lung disease: those with known etiologic agents and another group that are the result of abnormal immune responses, including autoimmunity.
Known etiologic agents for chronic interstitial lung disease include: inorganic dusts, drugs-- like chemotherapeutic agents (e.g. bleomycin) and toxins (e.g. paraquat).
Abnormal immune reactions are responsible for the majority of chronic interstitial pneumonias. These include: hypersensitivity reactions to inhaled organic material (e.g. farmer's lung), sarcoidosis, Goodpasture's syndrome, eosinophilic granuloma (histiocytosis X), collagen vascular diseases (e.g. SLE), and a group of poorly understood but surely autoimmune lung diseases known as "idiopathic pulmonary fibrosis".
Desquamative interstitial pneumonitis (DIP).
All of these diseases have some degree of progressive lung fibrosis and many end with severe scarring and cyst formation known as "honeycomb" lung. Patients experience slowly progressive shortness of breath.
The earliest pathologic manifestation of chronic interstitial pneumonia common to all of the disorders above is alveolitis-- inflammation of the alveolar wall. Fibrosis occurs when alveolar basement membranes are damaged.
Conceptually, the chronic interstitial pneumonias are like a slowly progressive brush fire burning across the lungs, leaving scarred remains in its path. The cause of many of these diseases is unknown, thus the wastebasket term "idiopathic pulmonary fibrosis".
Radiographically, these different disease entities all have in common reticulo-nodular densities involving both lungs-- in distributions that may be characteristic.
The clinical hallmark of chronic interstitial lung diseases is progressive shortness of breath with persistent non-productive cough.
- Diagnosis of these diseases often must rely on the open lung biopsy in order to secure sufficient tissue for accurate assessment.
- There is no effective therapy for most these diseases. High dose corticosteroids and even chemotherapeutic agents aimed at disarming the immune system are used commonly but remain unproven as curative therapies.

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