Acute Respiratory Distress Syndrome

Question 1

What is ARDS?

Answer 1

acute lung inflammation as a result of sepsis, pneumonia, trauma or aspiration.

Question 2

What can ARDS result in?

Answer 2

shock, either through direct ischaemic damage, or as a result of reperfusion damage.

Question 3

What are direct causes of ARDS?

Answer 3

trauma, aspiration pneumonia, fat embolism, alveolar haemorrhage

Question 4

What are indirect causes of ARDS?

Answer 4

sepsis, systemic trauma, shock, stroke, drug overdose (aspirin, heroin), burns, liver failure, pancreatitis, massive blood transfusion, head injury, pregnancy, eclampsia, malaria

Question 5

What is the pathology of ARDS?

Answer 5

results from local or systemic inflammatory processes. cytokines and other inflammatory mediators recruit macrophages and neutrophils to area. These then release other inflammatory agents, there is a disruption of the boundary between lung tissue and normal capillaries, leading to ‘leaking’ of blood products into air spaces. there is reduced lung compliance and disruption of surfactant leading to collapse of airways.

Question 6

What can ARDS be difficult to differentiate from?

Answer 6

acute heart failure and infection

Question 7

How is ARDS differentiated from acute heart failure?

Answer 7

by taking a pulmonary wedge pressure measurement

Question 8

What are the signs/symptoms of ARDS?

Answer 8

dyspnoea
tachycardia
tachypnoea
bilateral basal crepitations/other abnormal breath sounds 
chest pain 
peripheral vasodilation

Question 9

What must be present to diagnose ARDS?

Answer 9

• Acute onset
• Pulmonary capillary wedge pressure of <19mmHg
• CXR - demonstrating bilateral diffuse infiltrates
• refractory hypoxaemia - PO2:FiO2 <200

Question 10

What blood investigation would be used to diagnose ARDS?

Answer 10

amylase
FBC
U+E
CRP

Question 11

What would arterial blood gases be like in ARDS?

Answer 11

• low O2 - often does not respond well to prescribed O2
• pH - can be low initially (due to respiratory acidosis), or may be high in the presence of sepsis, or as result of underlying cause

Question 12

What would be seen on a chest X-ray in ARDS?

Answer 12

bilateral, widespread infiltrates. may take several hours to appear after onset of symptoms

Question 13

What is the mortality of ARDS?

Answer 13

50-75%

Question 14

What is the most important treatment for ARDS?

Answer 14

treat the underlying cause

Question 15

If ARDS caught early what treatment may be given?

Answer 15

40-60% O2

Question 16

why might mechanical ventilation be dangerous in ARDS?

Answer 16

high tidal volumes/pressures involved due to poor lung compliance, can lead to pneumothorax

Question 17

When might mechanical ventilation be considered in ARDS?

Answer 17

if given oxygen and ABG O2 remains <8.2kPa.

Question 18

What circulatory support may be given for ARDS?

Answer 18

• Give fluids
• consider pulmonary vasodilator to combat high intrapulmonary pressure (e.g. inhaled nitric oxide)
• consider an ionotrope (increase cardiac output without affecting rate) such as dobutamine