PATH: Neonatal, Developmental and Vascular Diseases Flashcards
What are the 2 broad causes of pulmonary edema?
Hemotynamic Forces
microvascular Injury
What are some hemodynamic forces that can lead to pulmonary edema?
increased hydrostatic pressure (common) decreased oncotic pressure (less common) lymphatic obstruction (rare)
What are some examples of microvascular injury that can lead to pulmonary edema?
shock (common) pulmonary infection (less common) inhaled toxins (much less common)
What is the MOST COMMON cause of pulmonary edema?
left sided heart failure
Why do “heart failure cells”= hemosiderin-laden macrophages collect in the alveoli in some cases of pulmonary edema?
Extremely high hydrostatic pressure can burst capillaries leading to microhemorrhages that are “cleaned up” by these macrophages
Where does fluid first accumulate in the lung after leaking out of capillaries?
septal capillaries–> interstitium–> airspaces
At what hydrostatic pressure does fluid leak from the capillaries and into the interstitium?
20 mmHg
At what pressure does fluid transudate out into the alveoli to cause pulmonary edema?
25 mmHg
What clinical sign of pulmonary edema will be seen before a patient develops pulmonary crackles?
dyspnea due to increased pulmonary venous pressure
What is the appearance of pulmonary edema fluid?
thin, white and frothy
What is the microscopic appearance of lung with pulmonary edema?
alveoli with thin, pale pink, finely granular material and the small blood vessels are congested
What is acute lung injury?
abrupt onset of hypoxemia and bilateral (radiographic) pulmonary infiltrates in the absence of heart failure
What value divides ARDS into its 3 different severities?
ratio of arterial oxygen pressure divided by fraction of inspired oxygen
(PaO2/FiO2)
What is a normal PaO2/FiO2?
476
100 mm Hg/ 0.21
What is the 4 most common causes of ARDS?
sepsis
diffuse pneumonia
gastric aspiration
trauma
What are the molecular mediators of early ARDS? What releases them?
TNF and IL-1 released by alveolar macrophages
What do TNF and IL-1 do in the alveoli?
activate endothelial cells making them put up adhesion molecules for neutrophils
What do neutrophils do in the alveoli?
they degranulate and release injurious proteases and ROSs
What is “Diffuse alveolar damage”?
histopathologic counterpart of ARDS
What occurs in the first 12-24 hours of diffuse alveolar damage?
congestion, interstitial and alveolar edema, and neutrophils (initially in capillaries, then interstitium and finally airspaces)
What occurs in the 24-72 hours following onset of diffuse alveolar damage?
loose granular pink edema fluid in the alveoli gradually condenses into dense, darker pink, smooth “hyaline membranes”
Why might you misdiagnose diffuse alveolar damage as cancer around the 2nd day of injury in diffuse alveolar damage?
type 2 pneumocytes start proliferating to replace dead type 1 cells (and look like cancer cells)
What happens to the hyaline membrane in diffuse alveolar damage?
it is gradually resolved over 3 weeks if the patient lives
What occurs around 72 hours following onset of diffuse alveolar damage?
lymphocytes, macrophages, and fibroblasts infiltrate the interstitium
What occurs in the organizing phase of diffuse alveolar damage?
granulation tissue forms in alveolar walls that may resolve or (if more severe) lead to scarring