ARDS

Question 1

What is ARDS?

Answer 1

• Severe hypoxaemia in absence of cardiogenic cause
• Occurs when inflammatory damage to alveoli –> pulmonary oedema, respiratory compromise and acute resp failure

Question 2

4 key definition points of ARDS

Answer 2

Berlin Definition:
* Acute onset within 7 days
* PaO2:FiO2 ratio <300 (with PEEP or CPAP >5cm H2O)
* Bilateral infiltrates on CXR
* Alveolar oedema not explained by fluid overload or cardiogenic causes

Question 3

Severity of ARDS

Answer 3

Degree of hypoxaemia via PaO2:FiO2 ratio
* Mild - 200-300mmHg
* Moderate - 100-200mmHg
* Severe - 100mmHg or less

Question 4

ARDS direct vs indirect causes

Answer 4

Direct:
* Pneumonia
* Smoke inhalation
* Aspiration
* Fat emboli

Indirect:
* Sepsis
* Acute pancreatitis
* Polytrauma
* Major burns

Question 5

Phases of ARDS

Answer 5

• Exudative
• Proliferative
• Fibrotic phase

Question 6

Exudative phase

Answer 6

• Diffuse alveolar damage initiated from tissue injury
• Cytokines and inflamamtory mediators released
• = direct alveolar and endothelial injury

Question 7

Proliferative phase

Answer 7

• Restoration of alveolar-capillary membrane integrity, achieved by fibroblasts and type 2 pneumocytes
• Attempt to normalise alveolar structure
• New surfactant produced

Question 8

Fibrotic phase

Answer 8

• Fibrin deposition across lungs –> scarring of tissue
• Lead to long term morbidity inc need for LTOT or even ventilation dependency

Question 9

Symptoms of ARDS

Answer 9

Worsening dyspnoea

Question 10

Examination findings of ARDS

Answer 10

• Hypoxia
• Tachypnoea
• Inspiratory crackles
• ACUTE ONSET <7 days is KEY

Question 11

Investigations for suspected ARDS

Answer 11

• ABG
• Routine bloods - FBC, U&E, CRP, amylase (identify cause)
• CXR
• Echo - exclude cardiac cause
• If CXR inconclusive can do CT thorax

Question 12

Management ARDS

Answer 12

• Ventilation
• Treat underlying cause
• Early intubation and ITU admission - resp and cardiac support

Question 13

Main aspects of ventilation management in ARDS

Answer 13

• Maintaining minimum intravascular volume - limit excess oedema but perfuse tissue
• Lower tidal volumes in ventilation - reduce shear forces from over distension and ventilation injury
• Positive end expiratory pressures - splinting airways and avoids damage caused by cyclical opening of alveoli

Question 14

If severely hypoxic despite ventilation, what can considered?

Answer 14

• ECMO
• = extra-corporeal membrane oxygenation