Acute respiratory distress syndrome

Question 1

What is ARDS?

Answer 1

ARDS or acute lung injury may be caused by direct lung injury or occur secondary to severe systemic illness. Lung damage and release of inflammatory mediators causes increased capillary permeability and non-cardiogenic pulmonary oedema, often accompanied by multi-organ failure.

Question 2

What causes/what are the risk factors for ARDS?

Answer 2

Pulmonary

• Pneumonia
• Gastric aspiration
• Inhalation injury (i.e. smoke)
• Vasculitis
• Pulmonary contusion

Other: shock, septicaemia, haemorrhage, multiple transfusion DIC, pancreatitis, acute liver failure, trauma, head injury, malaria, fat embolism burns, obstetric events (eclampsia, amniotic fluid embolus), drugs/toxins (aspirin, heroin)

Question 3

What are the features of ARDS?

Answer 3

• Cyanosis
• Tachypnoea
• Tachycardia
• Peripheral vasodilation
• Bilateral fine- inspiratory crackles

Question 4

How is ARDS diagnosed?

Answer 4

The following 4 criteria are required to confirm ARDS

1. Acute onset
2. CXR = bilateral infiltrate
3. Pulmonary capillary wedge pressure (PCWP) <19mmHg on pulmonary artery catheter, or a lack of clinical congestive heart failure
4. Refractory hypoxaemia with PaO2: FIO2 <200 for ARDS

Question 5

How is ARDS treated?

Answer 5

Admit to ICU, five supportive therapy and treat the underlying cause.

Respiratory support:
• Continuous positive airway pressure (CPAP) with 40-60% oxygen may be adequate to maintain oxygenation
• Ventilation may be required
Indication for ventilation = PaO2 <8.3kPa despite 60% O2, PaCO2 >6kPa.

Circulatory support
• Invasive haemodynamic monitoring (i.e. arterial monitoring)
• Conservative fluid management
• Maintain cardiac output and O2 delivery with ionotropes, vasodilators, and blood transfusions.

Septic support
• Identify organisms and treat accordingly

Nutritional support:
• Enteral nutritional support is best
• Steroids – protect those at risk of fat embolization and those with pneumocystis

Question 6

What is the prognosis like for ARDS?

Answer 6

Overall mortality is 50-75%. Prognosis varies with age of patient, cause of ARDS (pneumonia = 86%, trauma = 38%) and the number of organs involved (if more than 3 organs involved for >1 week = invariably fatal)