ARDS

Question 1

Define ARDS.

Answer 1

Acute respiratory distress syndrome =
a non-cardiogenic pulmonary oedema and diffuse lung inflammation syndrome that often complicates critical illness.

Question 2

What is the pathophysiology of ARDS?

Answer 2

Caused by the increased permeability of alveolar capillaries leading to fluid accumulation in the alveoli –> wet lung

There are dependent and non-dependent areas:
* dependent areas undergo dead space ventilation- all perfusion is in gravitational areas i.e. at bottom of lung on CT (low VQ)
* non-dependent areas undergo intrapulmonary shunting - where there is a lot of ventilation but not much perfusion (high VQ)

This causes **refractory hypoxaemia. **

Question 3

What are the risk factors/causes for ARDS?

Answer 3

• infection: sepsis, pneumonia, aspiration
• massive blood transfusion/haemorrhagic shock
• trauma
• smoke inhalation
• fat emboli
• prolonged mechanical ventilation
• acute pancreatitis
• cardio-pulmonary bypass

Question 4

How is ARDS diagnosed?

Answer 4

The diagnosis of ARDS is based on fulfilling three Berlin criteria:
* Acute onset (within 1 week)
* Bilateral opacities on CXR
* **Gas exchange abnormality **- PaO₂/FiO₂ (arterial to inspired oxygen) ratio of ≤300mmHg on PEEP OR CPAP ≥5 cm H₂O.
* Non-cardiogenic (pulmonary artery wedge pressure needed if doubt)

Question 5

What are the clinical features of ARDS?

Answer 5

Typically acute onset and severe:
* dyspnoea
* elevated RR
* bilateral lung crackles
* low O2 sats

Question 6

What is the management of ARDS?

Answer 6

Generally severe and managed in ITU
* oxygenation/ventilation to treat hypoxaemia
* organ support e.g. vasopressors as needed
* treat underlying cause e.g. antibiotics for sepsis
* prone positioning 16hrs/day
* neuromuscular blockers
* veno-venous ECMO in refractory hypoxaemia
* nitric oxide - pulmonary vasodilator to recruit blood flow to less perfused areas

Question 7

What are the complications of ARDS?

Answer 7

• death - ~40% risk
• VAP
• pneumothorax - from barotrauma
• organ failure - most commonly renal, shock, coma, delirium
• lung damage long term with dyspnoea
• reduced QoL

Question 8

What is the prognosis with ARDS?

Answer 8

1. 40% mortality
2. Those who recover experience obstructive lung disease and dyspnoea causing a reduced QoL
3. More than 50% of patients do not return to work a year after discharge from ICU
4. Muscle weakness, neuropathies, joint disorders, and chronic pain are also common in survivors of ARDS at 1 year.

Question 9

What are the complications of overventilation in ARDS?

Answer 9

VALI - overdistension of non-dependent areas will lung inflammation
Protective lung ventilation is used - driving pressures peaking at <25cmH2O

Question 10

What is the additional complication seen in COVID ARDS vs non-COVID ARDS?

Answer 10

Much higher incidence of PE in COVID ARDS than non-COVID ARDS

Question 11

How much is an ICU bed/day?

Answer 11

£3000/day

Question 12

What are the indications for ECMO?

Answer 12

• Within 7 days of ventilation
• Reversibility
• Adequate reserve in the patient
• Best for those with asthma and flu
• Not great for fibrosis or chronic lung disease
• Usually for single organ failure