Acute Respiratory Distress Syndrome

Question 1

A 76-year-old gentleman was admitted to the intensive care unit 4 days ago with shortness of breath secondary to a right lower lobe pneumonia. He was intubated and ventilated. He has a history of COPD, ischaemic heart disease and a hiatus hernia. You are asked to review this patient due to worsening type 2 respiratory failure.

What are the potential causes of his deterioration?

Answer 1

Equipment factors:

• Inappropriate ventilator settings.
• Malpositioned endotracheal tube.
• Blocked endotracheal tube or circuit.

Disease factors:
* New ventilator-associated/aspiration pneumonia.
* Sepsis.
* Over-sedated patient.
* Acute respiratory distress syndrome (ARDS).

Question 2

How is ARDS diagnosed?

Answer 2

• The 2012 Berlin definition can be used, which includes four criteria that need to be met for a diagnosis of ARDS to be made:
• Acute onset of symptoms (within 1 week of physiological insult or
  trauma).
• Bilateral pulmonary infiltrates (on chest X-ray or CT).
• Hypoxia with PEEP of at least 5cm H2O.
• Symptoms not explained by cardiac failure.
• ARDS can be defined as mild, moderate or severe depending on the degree of hypoxia. This is calculated using the PaO2/FiO2 ratio:
• Mild: PaO2/FiO2 ≤39.9 kPa.
• Moderate: PaO2/FiO2 ≤26.6 kPa.
• Severe: PaO2/FiO2 ≤13.3 kPa.

Question 3

What are the common causes for the development of ARDS?

Answer 3

Pulmonary:
* Pneumonia.
* Pulmonary contusion.
* Airway burns/smoke inhalation.
* Vasculitis.
* Drowning.

Extra-pulmonary:
* Sepsis.
* Massive blood transfusion.
* Polytrauma.
* Pancreatitis.
* Burns.
* Toxins.

Question 4

The patient assessment suggests a diagnosis of ARDS.

What is your initial approach to management?

Answer 4

• Ensure lung protective ventilatory strategies, to include:
• Tidal volume ≤6 mL/kg.
• Plateau pressures <30 cm H2O.
• PEEP >5 cm H2O.
• Respiratory rate 20–30.
• Permissive hypercapnia (raised PaCO2 if the pH >7.2).
• Titrated oxygen targets.
• Supportive management:
• Identify and treat the underlying cause.
• Consider neuromuscular blockade.
• Elevate the head of the bed.
• Judicious use of fluids.
• If the above measures do not demonstrate improvement, consider:
• Prone position ventilation.
• Extracorporeal membrane oxygenation.

Question 5

What are the common complications associated with placing patients in the prone position on intensive care?

Answer 5

• Pressure sores/ulcers.
• Facial oedema.
• Haemodynamic instability.
• Ocular oedema or injury.
• Nerve damage.
• Accidental removal of endotracheal tube and intravenous lines.
• Difficulty maintaining renal replacement therapy access.