ARDS Flashcards
What is ARDS?
A form of acute lung injury characterised by severe hypoxaemia in the absence of a cardiogenic cause.
There is inflammatory damage to the alveoli which leads to pulmonary oedema, respiratory compromise and ultimately acute respiratory failure.
Definition of ARDS
Berlin defintion
Acute onset within 7 days
PaO2:FiO2 ratio <300 (with PEEP or CPAP >5cmH2O
Bilateral infiltrates on CXR
Alveolar oedema not explained by fluid overload or cardiogenic cause.
Direct causes
Pneumonia
Smoke inhalation
Aspiration
Fat embolus
Indirect causes of ARDS
Sepsis
Acute pancreatitis
Polytrauma
Major burns
Pathophysiology
Divided into an exudative phase, proliferative phase and a fibrotic phase
Explain exudative phase
Diffuse alveolar damage from initial tissue injury.
Cytokines and various inflammatory mediators are all released that cause a direct alveolar and endothelial injury.
Explain proliferative phase
Restoration of alveolar-capillary membrane integrity by fibroblasts and T2 pneumocytes.
This is in order to try to normalise alveolar structure that has been damaged in the exudative phase.
New surfactant is produced as well.
Explain fibrotic phase
Extensive fibrin deposition across the lungs.
This leads to scarring of the lung tissue.
Substantial long-term morbidity follows where the patient might be dependent on long-term oxygen and ventilation therapy.
Clinical features
Worsening dyspnoea
Rapid hypoxia and tachypnoea
Inspiratory crackles on auscultation
One of the most characteristic features is the acute onset <7 days
Dx
CHF
ILD
Diffuse alveolar haemorrhage
Drug-induced lung injury
Investigations
ABG to assess hypoxia
Routine bloods with FBC, U&Es, amylase and CRP
CXR
CT thorax might be done if CXR is inconclusive
ECHO should also be performed to exclude a potential cardiogenic cause
CXR findings
Diffuse bilateral infiltrates
General management
Supportive treatment with ventilation
Focused treatment of the underlying
Highly likely you will need to intubate them early and ITU admission might be warranted and circulatory support.
What are the specific goals in ARDS management?
Limiting the inflammatory cascade
Reducing alveolar injury
How do you achieve the specific treatment goals
Maintaining the minimum intravascular volume to ensure adequate tissue perfusion.
Lower tidal volumes used in ventilation to reduce the shear forces from over-distension and ventilator associated lung injury.
Postive end-expiratory pressure by splinting the airways and avoids damage caused by the cyclical opening of alveoli.
