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21 Cards in this Set

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Define ARDS
Acute onset of dyspnea, bilateral infiltrates on CXR or CT, hypoxemia, absence of heart failure and presence of an inappropriate trigger.

Tends to occur in posterior parts of the lung while people lay supine
How do you measure hypoxemia
The P/F ratio. It is normally PaO2 over .21. It comes out to about 450. Falling below 300 is called acute lung injury. Falling below 200 is ARDS
How do you know it is ARDS and not CHF which is the most common cause of bilateral infiltrates?
A low PCWP suggests ARDS. We usually just do an echocardiography to check.

CHF responds to diuretics while ARDS does not
What triggers ARDS?
Direct injury: Aspiration, inhalation, infection, lung contusion, near drowning, fat/amniotic emboli, reperfusion

Indirect injury: Sepsis, severe non-thoracic trauma, blood transfusion, cardiopulmonary bypass, drug overdose, pancreatitis

Near drowning

Indirect is usually worse. Sepsis is the worst
Hyaline membranes
Pathognomonic lesion for ARDS
Pathophysiology of ARDS
Alveolar injury -> Flooding ->hyaline membranes -> Type I necrosis -> Hyperplasia of Type II -> Fibrosis
Describe the timeframe of ARDS
Edema in the first few days, development of hyaline membranes, inflammatory filtrate follows, and then fibrosis
What is the primary problem during the non-cardiogenic pulmonary edema phase of ARDS
Shunt physiology creates hypoxemia

Oxygen improves as edema resolves

When there people devolop interstitial thickening and fibrosis, the problem is ventilation/dead space
What does the lung look like following injury
There is diffuse alveolar damage which is associated with hyaline membranes.

DAD is not necessary for diagnosis of ARDS but it is pathognomonic for ARDS
Grossly what do DAD lungs look like?
They are heavy, full of blood, inflammatory cells, and protein?
Low vs High fluid management of ARDS
No difference in mortality but can get them out of ICU faster with low fluids. There is no association of low fluid strategy with more organ failures.
What if you use nitric oxide to treat ARDS?
It goes to well ventilated parts of lungs and dilates the pulmonary vasculature. Gas exchange improves and pulmonary artery pressure drops. It may have antiinflammatory effects.

When you go off of it, pulmonary htn rebounds. It is expensive. It does not improve survival rates

Rescue therapy only
What if you treat ARDS with corticosteroids?
May be harmful in acute phase.

No difference in 60-day mortality.

May reduce ventilatory days, ICU days, and reduce incidence of shock in the first month after injury

Complications were polyneuropathy and neuromuscular disease

May be high risk of death if you wait till after day 14 to start them.

So, there may be a window from 7-13 days when steroids are beneficial
What is the main strategy to deal with ARDS?
mechanical ventilation

-Don't use negative pressure like with polio
-Noninvasive positive pressure doesnt have high enough fraction of oxygen or enough pressure
-We use invasive positive pressure. Disadavantages are it is easy to catch an infection, and it is uncomfortable
PEEP?
Positive end expiratory pressure. Keeps alveoli from collapsing
What about compliance in ARDS?
Very low. You need high pressure air to get ventilation. Can lead to pneumothorax
What are the main complications of mechanical ventilation in ARDS
-Infection
-Hypotension
-Barotrauma is pressure trauma
-Sinusitis can develop.
-Ventilation prevents adequate sinus drainage so it can be aspirated.
-Pneumonia
-Ventilator-induced lung injury
Should you use high tidal volumes and pressure or not?
No because you can damage the lungs. It may release cytokines and inflammatory mediators. Can generate DAD. So you should probably tolerate poor gas exchange.

Low tidal volumes improves survival
Does the trigger matter in ARDS
Yes, direct is better than indirect. Trauma is best, sepsis is worst.

Mortality for ARDS is not predicted by initial gas exchange
what causes death with ARDS
1. Sepsis and progressive multi-organ failure
2. Respiratory causes
What pulmonary function is most likely to remain impaired in those surviving ARDS
CO diffusing capacity

Remember, most survivors have major problems in all areas of life afterwards