Acute respiratory distress syndrome

Question 1

Define acute respiratory distress syndrome

Answer 1

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

Diagnosis required:
• Acute onset
• Bilateral opacities on CXR
• PaO2/FiO2 ratio of <300 on PEEP/CPAP >5cm
• Lack of cardiac failure or pulmonary capillary wedge pressure <19

Acute respiratory distress syndrome (ARDS) is characterized by the development of acute dyspnoea and hypoxemia within hours to days of an inciting event

Question 2

Explain the aetiology of acute respiratory distress syndrome

Answer 2

Caused by many conditions
o Sepsis from a pulmonary source = most common
o Sepsis from non-pulm source = 2nd most common

Other associated conditions:
o Pulmonary: aspiration, inhalation (smoke), pneumonia, trauma, bypass, fat embolism and vasculitides
o Extra-pulmonary: haemorrhagic shock, burns, trauma, drug overdose, acute pancreatitis, many transfusions, DIC

Early pathological finding = diffuse alveolar damage
o Proteinaceous oedema fluid (exudate?)
o Inflammatory cells
o Inflammatory mediators – cytokines, lipid mediators, oxidants
o Epithelial injury – necrosis, type 1 cell sloughing

Question 3

Explain the risk factors of acute respiratory distress syndrome

Answer 3

• Sepsis
• Aspiration
• Pneumonia
• Severe trauma
• Blood transfusions
• Lung transplantation
• Pancreatitis
• Alcohol abuse history
• Burns/smoke inhalation
• Drug overdose
• Cigarette smoking

Question 4

Summarise the epidemiology of acute respiratory distress syndrome

Answer 4

• 10-15% of patients admitted to ICU
• 20% of all mechanically ventilated patients
• Mortality ~40%
• Incidence increases with age, reflecting the incidence of underlying causes

Question 5

Recognise the presenting symptoms of acute respiratory distress syndrome

Answer 5

• SOB

* Frothy sputum

Question 6

Recognise the signs of acute respiratory distress syndrome on physical examination

Answer 6

Obs - Low O2 saturation, Tachypnoea, tachycardia

Hands - Cyanosis

Chest - Low lung compliance, Bilateral rales

Respiratory failure

Symptoms of cause - Critically ill patient (Often with multiple organ failure)
Sepsis - Hypotension, Peripheral vasoconstriction

Distinguish from cardiogenic pulmonary oedema: signs of congestive heart failure (Exclude JVP distention, cardiac murmurs, gallops, hepatomegaly, oedema)

Question 7

Identify appropriate investigations for acute respiratory distress syndrome

Answer 7

First line
o	CXR - Bilateral infiltrates
o	ABG - Low paO2
o	Cultures (urine, sputum, blood) -  Infection
o	Lipase - Acute pancreatitis

Other investigations
o BNP - <100 nanograms
o Echo - Normal
o Pulmonary artery catheterisation - Occlusion pressure <18 mmHg
o Bronchoalveolar lavage - Identify infectious pathogens
o CT thorax - Identify pulmonary causes