Acute Respiratory Distress Syndrome

Question 1

What is ARDS?

Answer 1

An acute lung injury defined as respiratory distress, stiff lung with reduced lung compliance.

It may be caused by direct lung injury or secondary to severe systemic illness.

Question 2

Pathophysiology of ARDS.

Answer 2

Non-cardiogenic pulmonary oedema is the first and clinically most evident sign of a generalised increase in vascular permeability.

Pulmonary hypertension sometimes leading to pulmonary hypertension.

Haemorrhagic intra-alveolar exudate

Resolution, fibrosis and repair

Physiological changes where there is shunt and dead space increase, compliance falls and there is airflow limitation.

Question 3

What causes the non-cardiogenic pulmonary oedema in ARDS?

Answer 3

Microcirculatory changes and release of immune mediators.

Activated neutrophils as well.

Pulmonary epithelium is also damaged in the early stages, reducing surfactant production and predisposing to alveolar collapse.

Question 4

Causes of ARDS.

Answer 4

Pneumonia
Aspiration of gastric contents
Sepsis
Severe traum with shock and multiple transfusions

Pulmonary contusion

Fat embolism

Acute pancreatitis

Pulmonary vasculitis

Eclampsia

Malaria

Burns

Drugs

Question 5

Clinical features of ARDS.

Answer 5

Cyanosis

SOB

Tachypnoea

Tachycardia

Peripheral vasodilation

Bilateral fine inspiratory crackles

Question 6

Investigations done in ARDS.

Answer 6

FBC, U&Es, LFT, Amylase, Clotting, CRP, Blood cultures, ABGs.

CXR

Pulmonary artery catheter to measure pulmonary capillary wedge pressure might be done.

Question 7

CXR findings in ARDS.

Answer 7

Bilateral diffuse shadowing, interstitial at first but subsequently with an alveolar pattern and air bronchograms.

Question 8

Diagnostic criteria of ARDS.

Answer 8

All 4.

1 - Acute onset

2 - Bilateral infiltrates on CXR

3 - PCWP < 19 mmHg or a lack of clinical congestive heart failure

4 - Refractory hypoxaemia with PaO2:FiO2 < 200.

Question 9

Management of ARDS.

Answer 9

Admit to ITU, give supportive therapy and treat underlying cause.

Resp support - CPAP with 40-60% O2. However most patients will need mechanical ventilation. - Indications such as PaO2 < 8.3 kPa despite 60% O2 and PaCO2 > 6 kPa.

Circulatory support - Invasive haemodynamic monitoring with an arterial line and Swan-Ganz catheter aids the diagnoiss and may be helpful in monitoring PCWP and cardiac output. Conservative fluid management. Inotropes and blood transufions.

Inhaled Nitric oxide as a vasodilator to treat pulmonary HTN.

Diuretics to treat oedema or possible haemofiltration if not enough.