Acute Respiratory Distress Syndrome

Question 1

Define ARDS

Answer 1

Syndrome of acute and persistent lung inflammation with increased vascular permeability.

Question 2

What characterises ARDS

Answer 2

Acute onset
Bilateral infiltrates consistent with pulmonary oedema
Hypoxaemia
No evidence of increases left atrial pressure (PCWP< or equal to 18)
ARDS is the severe end of the spectrum of acute lung injusry

Question 3

Pathology of ARDS

Answer 3

Severe insult to the lungs or other organs induces the release of inflammatory mediators, increased capillary permeability, pulmonary oedema, impaired gas exchange and decreased lung compliance

Question 4

causes of ARDS

Answer 4

Sepsis
Aspiration
Pneumonia
Pancreatitis
Trauma/burns
Transfusion (TRALI)
Transplantation 
Drug overdoes/reaction

Question 5

pathological stages

Answer 5

exudative –> proliferative –> firbrotic

Question 6

Symptoms

Answer 6

rapid deterioration in respiratory function

breathless, cough, symptoms of aetiology

Question 7

Signs

Answer 7

Cyanosis, tachynpoea, tachycardia, widespread inspiratory crepitations, hypoxia refractory to oxygen treatment

Question 8

Investigations

Answer 8

Chest x-ray (bilateral alveolar and intersitial shadowing)
Bloods (FBC, UE, LFT, ESR/CRP, amylase, clotting, ABG, blood culture, sputum culture, plasma BNP (to distinguish from heart failure).
ECHO (to exclude cardiac cause)
Pulmonary artery catherterisation (PCWP less than 18)
Bronchoscopy (if cause cannot be determined from history to exclude differentials.

Question 9

Management

Answer 9

Oxygen - most patients require intubation and mechanical ventilation
Sedation and analagesia. Neuromuscular blocks can be used if sedation inadequate
Fluids are conservative unless hypotensive or organ hypo perfusion. Blood transfusion if HB less than 7g/dL.
Enteral feeding, control blood glucose.
Treat cause
Treat/prevent complications

Question 10

Complications of ARDS

Answer 10

Respiratory failure and death
Complications related to mechanical ventilation ( pneumothorax, surgical emphysema, nosocomial pneumonia)
DVT, GI bleed

Question 11

Prognosis

Answer 11

Variable depends on cause.
60 percent if from sepsis,
Mortality increases with age, sepsis, steroid treatment prior to onset. ARDS associated with trauma has lower mortality

Question 12

How is the patient ventilated in ARDS

Answer 12

using a low tidal volume ventilation technique
he rationale for LTVV is that smaller tidal volumes are less likely to generate alveolar overdistension and ventilator-associated lung injury. LTVV frequently requires ‘permissive hypercapnic ventilation’, a ventilatory strategy that accepts alveolar hypoventilation in order to maintain a low alveolar pressure and minimize the complications of alveolar overdistension.