Acute Respiratory Distress Syndrome

Question 1

What is Starling’s equation governing edema fluid formation?

Answer 1

QE = K_F [(P_mv - P_is) - σ(π_mv - π_is)]

K_F 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

Question 2

Acute Respiratory Distress Syndrome (ARDS)

Answer 2

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)

Question 3

mechanisms involved in fluid clearance from the lungs

Answer 3

active Na+ transport

lymphatics

reabsorption into blood vessels

Question 4

acute lung injury (ALI)

Answer 4

used for mild ARDS patients who have P/F ratios beftween 200 and 300

Question 5

staging of ARDS

Answer 5

P/F ratio 300 to 200 - mild

P/F ratio 200 to 100 - moderate

PF ratio = 100 - severe

Question 6

normal P/F ratio

Answer 6

PaO₂/FiO₂ >/= 450

Question 7

at-risk conditions for ARDS

Answer 7

sepsis

aspiration

pneumonia

shock

multiple blood transfusions

drug overdose

fat embolism

pancreatitis

cardiopulmonary bypass

trauma

inhalation injury

pulmonary contusion

Question 8

What are some possible advances in supportive care that have been shown to decrease the incidence of ALI?

Answer 8

use of low tidal volumes during mechanical ventilation

earlier treatment of sepsis

decreased transfusion of blood products

Question 9

What is the disease progress of ALI/ARDS?

Answer 9

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)

Question 10

ARDS mechanisms of injury

Answer 10

1. activation of inflammatory mediators and cellular components resulting in damage to capillary endothelial and alveolar epithelial cells
2. increased permeability of the alveolar-capillary membrane
3. influx of protein-rich edema fluid and inflammatory cells into the airspaces
4. dysfunction of surfactant
5. abnormalities of the coagulation system - platelet-fibrin thrombi in small vessels and impaired fibrinolysis within distal spaces of the injured lung
6. abnormalities in production, composition, and function of surfactant that contribute to alveolar collapse and gas-exchange abnormalities
7. ventilator-induced lung injury (VILI)
8. potential for aberrant repair/fibrosis

Question 11

DAD

Answer 11

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

Question 12

methods of treating ARDS

Answer 12

increase FiO₂

low tidal volume ventilation

faster respiratory rates

positive end expiratory pressure (PEEP)

sedation/analgesia/paralysis

prone positioning