RESPIRATORY DISTRESS SYNDROME Flashcards
What is respiratory distress syndrome characterised by?
Rapid onset of widespread inflammation in the lungs
A medical emergency
bilateral pulmonary infiltrates and severe hypoxemia (PaO2/FiO2 ratio < 200) in the absence of evidence for cardiogenic pulmonary oedema
Whats the main site of injury in respiratory distress syndrome?
Alveolar-capillary membrane (becomes more permeable -> pulmonary oedema)
What causes respiratory distress syndrome?
Direct lung injury - e.g. pneumonia which is the most common cause
Sepsis
Aspiration
Trauma
Acute pancreatitis
Long bone fractures - fat embolisms
Head injury - sympathies nervous stimulation can cause acute pulmonary hypertension
Transfusion reactions
Outline the pathophysiology of respiratory distress syndrome?
Initial insult -> injury to alveolar capillary membrane -> increased permeability of membrane -> pulmonary oedema/ acute inflammatory exudate -> hypoxaemia and washes away surfactant in alveoli so it cannot reduce the surface tension any more = alveoli collapse
In response we get hypoxic pulmonary vasoconstriction -> hypoxaemia and eventually type 2 respiratory failure
In response to this inflammatory mediators are released e.g. neutrophils, TNF alpha, Il-1, IL-8 which further exacerbate inflammation and damage the lungs as well as other organs
Note: it causes hyaline membrane formation
What are the 2 stages of respiratory distress syndrome?
Early stages consist of an exudative phase of injury with associated oedema.
The later stage is one of repair and consists of fibroproliferative changes. Subsequent scarring may result in poor lung function.
What are clinical features of respiratory distress syndrome?
Acute dyspnoea and hypoxaemia hours/days after event
Fever
Tachypnoea and hypotension
Chest pain
Hypoxia
Cyanosis
Multi organ failure
Bilateral bibasal crackles on auscultation
Sympotms indicative of cause e.g. abdo pain radiating to back = pancreatitis
What may ARDS present the same as?
Acute heart failure
What investigations should you do for ARDS?
Amylase
FBC
U&Es
CRP
ABG - low O2 and low/high pH
CXR - bilateral, widespread infiltrates
Pulmonary catheter to measure pulmonary capillary wedge pressure (<19mmHg)
What are the 4 diagnostic criteria for adult respiratory distress syndrome?
Acute onset - within1. Week
Bilateral infiltrates seen on CXR
Hypoxaemia that doesn’t improve with administartion of supplemental oxygen
Absence of left atrial hypertension (measure pulmonary artery wedge pressure)
How do you manage ARDS?
Ventilators support - a low tidal volume is associated with best outcomes
Treat underlying cause -
Negative fluid balance with diuretics
Prone positioning to improve ventrilation or use of positive end-expiratory pressure
Antibiotics if signs of sepsis or pneumonia
