ARDS (2) Flashcards

(51 cards)

1
Q

Characteristics of ARDS on histological examination?

A
  • Diffused alveolar damage
  • Oedema
  • Cell necrosis
  • Fibrosis
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2
Q

What was the initial definition of ARDS?

A
  • Acute onset hypoxia
  • PaO2 to FiO2 ration < 200mmHg
  • Bilateral infiltrates on CXR
  • PAWP < 18mmHg or cardiogen pul oedema
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3
Q

What is the current Berlin definition of ARDS?

A
  • Acute onset ARDS within 7 days of insult
  • Degree of hypoxia based on PaO2/FiO2
  • PEEP of at least 5
  • Absence of fluid overload or CCF
  • Infiltrates on CXR & CT
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4
Q

Classification of ARDS based on degree of hypoxaemia (PaO2/FiO2 ratio)?

A
  • Mild - 201 and 300
  • Moderate - 101 and 200
  • Severe - <100 mmHg
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5
Q

Characteristics of ARDS?

A
  • Precipitated by underlying factors
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6
Q

Distinguishing between types of ARDS?

A
  • Pulmonary
  • Extra-pulmonary
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7
Q

What is pulmonary ARDS?

A

Direct insult to the lung affecting pulmonary epithelium

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8
Q

What is extra-pulmonary ARDS?

A

Indirect lung injury caused by inflammatory mediators acting on vascular endothelium

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9
Q

What are the causes of pulmonary ARDS?

A
  • Pneumonia (Main cause)
  • Aspiration pneumonitis
  • Inhalation injury
  • Pulmonary contusion
  • Pulmonary vasculitis
  • Near drowning
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10
Q

What are the causes of extra-pulmonary ARDS?

A
  • Non-pulmonary sepsis
  • Non-cardiogenic shock
  • Pancreatitis
  • Major trauma
  • TRALI
  • Burns
  • Drug overdose
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11
Q

What are the mimics of ARDS?

A
  • Vasculitis (Alveolar haemorrhage)
  • Drug induced
  • Eosinophilic pneumonia
  • Interstitial pneumonia
  • Lung mets (Cancer)
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12
Q

What are the phases of ARDS pathophysiology?

A
  • Exudative
  • Proliferative
  • Fibrosis
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13
Q

Features of the exudative phase of ARDS?

A
  • Capillary congestion
  • Alveolar oedema
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14
Q

Features of the proliferative phase of ARDS?

A
  • Proliferation of alveolar Type-2 cells
  • Proliferation of fibroblasts
  • This phase can lead to resolution or formation of fibrosis
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15
Q

What are the intrapulmonary causes of hypoxaemia in ARDS?

A
  • Shunt
  • Dead space
  • Impairment of gas diffusion
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16
Q

What are the mechanisms contributing to hypoxaemia in ARDS?

A
  • Epithelial damage and increased shunt
  • Endothelial damage and increased dead space
  • Interstitial damage and impaired diffusion
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17
Q

Explain the mechanism of epithelial damage and increased shunt?

A
  • Primary cause of hypoxaemia in ARDS
  • Loss of lung volume - Surfactant deficiency
  • Alveolar oedema
  • Lung collapse
  • Intraplulmonary shunt
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18
Q

Explain the mechanism of Endothelial damage and increased dead space ?

A
  • Abnormalities in pulmonary blood flow
  • The lung region is usually well ventilated
  • Surrogate for dead space is ventilatory ratio
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19
Q

Explain the mechanism of Interstitial damage and impaired gas diffusion?

A
  • Interstitial oedema
  • Hyaline membrane
  • Fibrosis - Thickened alveolar-capillary memebrane
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20
Q

What are the components of ventilator induced lung injury ? (VILI)

A
  • Volutrauma
  • Barotrauma
  • Atelectrauma
  • Biotrauma
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21
Q

Risk factors of VILI?

A
  • High end-inspiratory lung volume
22
Q

What is volutrauma?

A

This is high end-inspiratory lung volume

23
Q

Factors promoting volutrauma?

24
Q

What is lung strain?

A

This is the ratio of VT to end-expiratory lung volume. Excess in strain results from high VT or high PEEP which brings the end-expiratory lung volume closer to TLC

25
What are the risk factors for barotrauma?
- Lung hyper-inflation
26
What is atelectrauma?
This is due to the repeat opening and closing of the small airway over the breathing cycle at low tidal volumes.
27
Factors promoting atelectrauma?
- Surfactant deficiency - Alveolar instability - Oedema - Increased permeability - Inflammation - Structural damage - Fibrin accumulation - Fibrosis
28
How can atelectrauma be be prevented?
- Application of high PEEP
29
What is biotrauma?
- Release of inflammatory mediators - Oxygen toxicity
30
What are the major determinants of VILI and in-hospital mortality ?
- Driving pressure (Plateau pressure - PEEP) - Mechanical power
31
Phenotype of Covid-19?
- Type L
32
Characteristics of L-type covid-19?
- Low elastance (i.e high compliance) - Low ventilation/perfusion ratio - Low lung weight - Low recruitability
33
Characteristics of type-H ARDS sub-phenotype?
- High elastance (Low compliance) - High right to left shunt - High lung weight - High recruitability
34
What is the ventilatory strategy for the L-type phenotype?
- High VT 8-9ml/kg - Low PEEP
35
What is the ventilatory strategy for the H-type phenotype?
- Low VT - High PEEP - Prone ventilation
36
What is compliance ? How is it calculated
- Tidal volume divided by driving pressures - Combination of lung/chest wall compliance - Chest wall compliance > lung compliance
37
What is the average value of the respiratory system compliance?
30ml/cmH2O or less
38
Factors increasing respiratory system resistance?
- Low lung volumes
39
Methods of measuring chest wall compliance?
- Oesophageal pressure
40
What is the influence of compliance on plateau pressure and driving pressure
- Relevant in intra-abdominal pathology
41
What are the methods of oxygenating patients ?
- CPAP - HFNC - NIV
42
What is the ROX index?
- Ratio between sats & FiO2 - High respiratory rate - Predicts therapy failure in pts on HFNC
43
What is the HACOR scale?
Predicts NIV failure by evaluating; - HR - Acidosis - GCS - RR
44
What is the driving pressure?
- VT / Compliance - > 15cmH2O is high risk for mortality
45
What is the volume of oxygen and flow rate that can be delivered during ECMO?
- 400ml O2/min - Flow 6L/min
46
Characteristics of the Extracorporeal CO2 removal?
- CO2 clearance 150-200ml/min - Veno-venous blood flow (1-2L/min)
47
What are the characteristics of the High Frequency Oscillatory Ventilation?
- 900 cycles/min
48
What are the advantages of iNO in ARDS ?
- Selectively dilates pulmonary vessels - Improves oxygenation (preserved HPV) - Reduction of PVR
49
What are the components of the total peak pressure? This can be separated in VCV
- Resistive (Peak pressure - Plateau pressure) - Elastic (plateau pressure)
50
What is End-Expiratory Lung Volume ?
- Amount of aerated lung at the end of exp - Evaluates collapse or over-distention - Assessment of the effect of PEEP - Its underestimated by bedside - Circuit leaks can compromise measurement
51
What is acute cor-pulmonale?
- Increased RV afterload - Complication of ARDS - Increased HPV & compression pul capillaries - Increased PVR - Dilated RV & septal dyskinesia