Acute respiratory stress syndrome

Question 1

Define ARDS

Answer 1

• Acute respiratory distress syndrome (ARDS) is a non-cardiogenic pulmonary oedema and diffuse lung inflammation syndrome that often complicates critical illness.

Question 2

What is ARDS characterised by?

Answer 2

Characterised by:
o Acute onset (within 1 week)
o Bilateral infiltrates on chest x-ray
o Hypoxaemia (Pa02/FiO2 ratio of less than/equal to 300 on Positive End-Expiratory Pressure (PEEP)
o No clinical evidence of increased left arterial pressure (pulmonary capillary wedge pressure)
o ARDS is the severe end of the spectrum of acute lung injury

Question 3

Explain the aetiology of ARDS

Answer 3

• Severe insults to the lungs and other organs leads to the release of inflammatory mediators
• Generalised inflammatory response with endothelial dysfunction – associated with MODS (multiple organ dysfunction syndrome).
• These lead to increased capillary permeability, pulmonary oedema, impaired gas exchange and reduced lung compliance

Question 4

What are the causes of ARDS?

Answer 4

o	Sepsis (most common)
o	Aspiration 
o	Pneumonia 
o	Trauma/burns
o	Pancreatitis
o	Burns and smoke inhalation
o	Blood transfusions
o	Lung transplantation
o	History of alcohol misuse
o	drowning

Question 5

What are the 3 stages of ARDS?

Answer 5

o Exudative
o Proliferative
o Fibrotic

• Oedema may induce vascular compression resulting in pulmonary hypertension
• Haemorrhagic intra-alveolar exudate forms, rich in platelets, fibrin and clotting factors. Inactivates surfactant, stimulates inflammation and promotes hyaline membrane formations. Leads to progressive pulmonary fibrosis.

Question 6

Epidemiology of ARDS

Answer 6

• Annual UK incidence: 64/100000

* 10-15% patients in ICU meet criteria for ARDS

Question 7

What are the presenting symptoms of ARDS?

Answer 7

• Rapid deterioration of respiratory function
• Dyspnoea (most common)
• Respiratory distress
• Cough
• Symptoms of CAUSE

Question 8

What are the clinical signs of ARDS?

Answer 8

• Cyanosis
• Tachypnoea
• Tachycardia
• Widespread inspiratory crepitations
• Hypoxia refractory to oxygen treatment
• Signs are usually bilateral but may be asymmetrical in early stages
• Low lung compliance (tidal volume/PEEP)

Question 9

What are the 1st investigations to order for ARDS and the results?

Answer 9

• CXR - bilateral alveolar infiltrates and interstitial shadowing
• Bloods - to figure out the cause (FBC, U&Es, LFTs, ESR/CRP, Amylase, ABG, Blood Culture)
o Pa02/FiO2 ratio of less than/equal to 300 on PEEP or CPAP of greater than/equal to 5cm H2O
o Serum amylase and lipase can check for acute pancreatitis (3x normal levels in acute pancreatitis)
• Sputum culture (check for infection as sepsis)
• Urine culture (check for infection)

Question 10

What are some investigations to consider for ARDS?

Answer 10

• Plasma Brain Natriuretic Peptide < 100 pg/mL could distinguish ARDS from heart failure, >500 make HF more likely
• Echocardiography
o Check for severe aortic or mitral valve dysfunction
o Abnormal left ventricular function suggests cardiogenic pulmonary oedema rather than ARDS.
• Pulmonary Artery Catheterisation
o Check pulmonary artery occlusion pressure,