Acute Respiratory Distress Syndrome Flashcards
What is Starling’s equation governing edema fluid formation?
QE = KF [(Pmv - Pis) - σ(πmv - πis)]
KF is the filtration coefficient, increases with increasing permeability or surface area
σ is the reflection coefficient for preoteins - values range from 1 if completely impermeable to 0 if completely permeable
Acute Respiratory Distress Syndrome (ARDS)
a form of pulmonary edema that is non-cardiogenic
a state of acute lung injury resulting in bilateral lung infiltrates and hypoxemia (P/F ratio = 300)
mechanisms involved in fluid clearance from the lungs
active Na+ transport
lymphatics
reabsorption into blood vessels
acute lung injury (ALI)
used for mild ARDS patients who have P/F ratios beftween 200 and 300
staging of ARDS
P/F ratio 300 to 200 - mild
P/F ratio 200 to 100 - moderate
PF ratio = 100 - severe
normal P/F ratio
PaO2/FiO2 >/= 450
at-risk conditions for ARDS
sepsis
aspiration
pneumonia
shock
multiple blood transfusions
drug overdose
fat embolism
pancreatitis
cardiopulmonary bypass
trauma
inhalation injury
pulmonary contusion
What are some possible advances in supportive care that have been shown to decrease the incidence of ALI?
use of low tidal volumes during mechanical ventilation
earlier treatment of sepsis
decreased transfusion of blood products
What is the disease progress of ALI/ARDS?
first few days - watery/proteinaceous edema fluid (edematous stage, days 1-2)
after 1-2 days - hyaline membranes form and there is diffuse alveolar damage (exudative stage, days 2-7)
interstitial inflammation and fibrosis beings in the first few days, but by days 7-10, it may be the predominant problem (proliferative phase, day 7 and on)
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ARDS mechanisms of injury
- activation of inflammatory mediators and cellular components resulting in damage to capillary endothelial and alveolar epithelial cells
- increased permeability of the alveolar-capillary membrane
- influx of protein-rich edema fluid and inflammatory cells into the airspaces
- dysfunction of surfactant
- abnormalities of the coagulation system - platelet-fibrin thrombi in small vessels and impaired fibrinolysis within distal spaces of the injured lung
- abnormalities in production, composition, and function of surfactant that contribute to alveolar collapse and gas-exchange abnormalities
- ventilator-induced lung injury (VILI)
- potential for aberrant repair/fibrosis
DAD
diffuse alveolar damage
Proteinacious cellular material interferes with alveolar function
Hyaline membrane - pink membrane made up of fibrous tissue
Classic for this type of lung injury
Interstitium also has inflammation
Lung is damaged, barrier from vessel to interstitium is damaged
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methods of treating ARDS
increase FiO2
low tidal volume ventilation
faster respiratory rates
positive end expiratory pressure (PEEP)
sedation/analgesia/paralysis
prone positioning