ARDS Flashcards
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
What imaging results are associated with ARDS?
Bilateral opacities similar to pulmonary edema appear on CXR or CT scan
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
How can you rule out a cardiogenic source when considering ARDS?
Cxr to look at the cardiac silhouette
Echocardiogram
How is the severity of ARDS determined?
The P/F ratio
Mild ARDS would be characterized by a P/F ratio of what?
201-300
Moderate ARDS would be characterized by a P/F ratio of what?
101-200
Severe ARDS would be characterized by a P/F ratio of what?
Less than 100
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
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
Describe the fluid produced in CHF
Transudate
Thin, watery fluid that is protein poor
Describe the fluid found in non-cardiogenic pulmonary edema
Exudate
Protein rich
Macrophages, neutrophils
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
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
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
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
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
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
What is the most common cause of ARDS?
Sepsis
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
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
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
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
