ARDS Flashcards by Ezekiel McGinn

According to the berlin definition, what is the timing parameter needed to consider ARDS?

The respiratory conditions associated with ARDS must manifest within 1 week of a known clinical event

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What imaging results are associated with ARDS?

Bilateral opacities similar to pulmonary edema appear on CXR or CT scan

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What specific distinction must we be able to make about the bilateral opacities in order to support a diagnosis of ARDS?

The opacities cannot fully be explained by pleural effusion, lobar or lung collapse or pulmonary nodules
The edema cannot have a cardiogenic source

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How can you rule out a cardiogenic source when considering ARDS?

Cxr to look at the cardiac silhouette
Echocardiogram

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How is the severity of ARDS determined?

The P/F ratio

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Mild ARDS would be characterized by a P/F ratio of what?

201-300

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Moderate ARDS would be characterized by a P/F ratio of what?

101-200

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Severe ARDS would be characterized by a P/F ratio of what?

Less than 100

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What is the Frank Starling Law and what does it describe?

It describes net fluid movement out of a capillary based on capillary and interstitial hydrostatic and oncotic pressure

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What portion of the frank starling law does congestive heart failure affect?

In congestive heart failure, capillary hydrostatic pressure is increased which results in more fluid being pushed out of the capillaries and into the interstitium

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Describe the fluid produced in CHF

Transudate
Thin, watery fluid that is protein poor

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Describe the fluid found in non-cardiogenic pulmonary edema

Exudate
Protein rich
Macrophages, neutrophils

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What can happen if a pleural effusion is drained too rapidly?

Decompression pulmonary edema
Fluid leaving the space creates a negative pressure area which can pull fluid out of the capillaries and into the alveoli

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What can cause a decrease in intrapleural pressure?

Someone with an upper airway restriction gasping for breath can drive pressure down enough to cause a fluid shift
This is known as a self induced lung injury

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Describe how altitude can cause a pulmonary edema

Forceful breathing at higher altitudes due to not being acclimated can cause a fluid shift into the alveoli due to the individual generating such a large negative pressure by breathing very forcibly

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What can cause a decrease in capillary oncotic pressure?

Overtransfusion
Uremia = elevated urea concentration in blood
Malnutrition aka hypoproteinemia
Acute nephritis = inflammatory kidney disease
Polyarteritis nodosa = necrotic inflammation of blood vessels

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Describe how ARDS is different from cardiogenic edema

Capillary permeability caused by ARDS results in alveoli being filled with exudate
A patient with ARDS can have no cardiogenic issues associated with the pulmonary edema
ARDS significantly impacts oxygenation and is resistant to treatment with CPAP

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What are some additional conditions/behaviors that can cause pulmonary edema?

Allergic reaction to drugs
Excessive sodium consumption
Drug overdose
Metal poisoning
Chronic alcohol ingestion
Aspiration

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What is the most common cause of ARDS?

Sepsis

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Why does sepsis frequently result in ARDS?

Sepsis is a dysregulated host response to an infection. As part of the inflammatory process, excessive capillary permeability can result in the alveoli being flooded with fluid and lymphocytes that can attack the alveoli directly resulting in more inflammation and damage

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What criteria must be met in order to diagnose sepsis?

Temp >38.3 or < 36
HR > 90 bpm
RR > 20 or PaCO2 < 32 mmHg
WBC > 12000 or >10% Bands
And a sepsis induced organ dysfunction

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Give some examples of sepsis induced organ dysfunction?

Hypotension
Lactate > 2 mmol (evidence of anaerobic metabolism)
Creatinine > 2.0 mg/dL
Total bilirubin > 2.0 mg/dL
Platelets < 100k per microliter
Coagulopathy
Encephalopathy
Acute respiratory failure

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What are examples of direct initial injuries that could lead to ARDS?

Pneumonia
Aspiration of gastric contents
Lung contusions
Near drowning
Smoke inhalation

What are examples of indirect initial injuries that can lead to ARDS?

Sepsis
Pancreatitis
Multiple long bone fractures releasing a fat embolis
Transfusion associated lung injury
Drug use

What drugs are associated with ARDS?

Amiodarone = heart medication Self injected IV drugs

T/F: ARDS cannot be caused iatrogenically

False. Mechanical ventilation and oxygen toxicity can result in ARDS. Along with certain prescription drugs that can have adverse reactions like amiodatone

Describe the hyaline membrane that forms as a result of ARDS

Increased capillary permeability results in neutrophils entering the alveoli and releasing reactive oxygen species and proteases which damage the type one and 2 cells resulting in cellular debris, increased inflammation, dead cells, RBCs and fibrin creating a layer of junk that forms over the walls of the alveoli

What is the result of the formation of a hyaline membrane?

Severely compromised gas exchange

ARDS causes significant changes in ventilation. Explain these changes and the physiologic effects that they have on the lungs.

In healthy lungs, a stress is distributed uniformly in the lungs. In lungs with ARDS, there are areas of consolidation with lowered compliance. These areas of lower compliance result in heterogenous distribution of the stress which causes alveoli near the consolidation to experience more stress which can result in damage

What are the stages of ARDS?

Exudative phase (within 72 hours) Proliferative phase (4-14 days) Fibrotic phase (14-21 days)

Describe the exudative phase of ARDS

Interstitial edema Acute and chronic inflammation Type 2 cell hyperplasia Hyaline membrane formation

Describe the proliferative phase of ARDS

Resolution of pulmonary edema Proliferation of type 2 cells Squamous metaplasia

Describe the fibrotic stage

Obliteration of normal cell architecture Fibrosis Cyst formation

Do all patients enter the fibrotic stage of ARDS?

No, less severe cases of ARDS do not necessarily end with fibrosis

What hemodynamic indices could be indicative of ARDS?

Increased pulmonary arterial pressure Decreased PCWP Increased PVR

Describe PFT findings if you were to force a patient with ARDS to take a PFT because you hate them

Decreased capacities, some flows may be normal but will likely be decreased depending on the underlying condition Volumes will be down

What is the difference in appearance between edema caused by ARDS and edema caused by CHF?

ARDS = ground glass and more diffuse CHF = fluffy and somewhat centralized

Should patients with ARDS receive systemic corticosteroids?

Corticosteroids should be used on patients with ARDS Corticosteroids may be associated with increased risk of harm after prolonged mechanical ventilation

What level of severity of ARDS calls for use of systemic corticosteroids?

Mild through severe

Should patients with ARDS receive higher levels of PEEP?

Higher PEEPs should be used without LRM in patients with moderate to severe ARDS Respiratory mechanics, hemodynamics and response to PEEP should be continuously monitored in order to determine whether or not higher PEEP is helping or harming

What level of severity of ARDS calls for potential use of higher PEEP?

Moderate to severe

Should NMBAs be used on patients with ARDS?

NMBAs can be used on patients with early severe ARDS however the recommendation is conditional and there isnt a lot of evidence that demonstrates a benefit

What level of severity of ARDS calls for potential use of NMBAs?

Severe ARDS

Should patient with ARDS be put on ECMO?

ECMO can be used on select patients with ARDS Other methods such as lung protective ventilation, prone positioning and NMBAs should be initiated prior to considering ECMO

Should patients with ARDS be proned?

Patients with moderate to severe ARDS are strongly recommended to be positioned in prone

What benefit does prone positioning have for patients with ARDS?

Changes V/Q matching Takes the weight of the heart off the lungs Redistributes regional blood flow

What is ARDSnet?

ARDSnet was a study that found that lower tidal volumes significantly increased survival rates in patients with ARDS and significantly reduced the risk of ventilator derived injuries

What are the ARDSnet recommendations for tidal volume?

6-8 ml/kg of IBW

What are the ARDSnet recommendations for Pplat?

25-30 cmH2O

What are the ARDSnet recommendations for PaO2 or SpO2?

55-80 mmHg or 88-95%

What are the ARDSnet recommendations for pH?

7.3-7.45

In essence, what is the goal of ARDSnet in regards to ventilation?

Abandon attempts to reinflate collapse or inundated alveoli Focus on ventilating functional portions of the lung without causing more damage by attempting high pressure recruitment maneuvers

How does APRV rival ARDSnet?

APRV is used to keep the lung open as much as possible using CPAP and dropping pressure at regular intervals to flush out CO2 Apparently worked on pigs

What are the recommendations for driving pressure in regards to ARDS?

Decreased delta P was strongly associated with increased survival Target a delta P of less than or equal to 15 cm H2O

What do prostaglandins cause?

Increased capillary permeability Altering vascular smooth muscle tone

What are endotoxins?

Proteins present on the membranes of gram negative bacteria which can provoke a significant immune response