Related Subjects: Asthma |Acute Severe Asthma |Exacerbation of COPD |Pulmonary Embolism |Cardiogenic Pulmonary Oedema |Pneumothorax |Tension Pneumothorax |Fat embolism |Hyperventilation Syndrome |Acute Respiratory Distress Syndrome (ARDS) |Respiratory Failure | |Non invasive ventilation (NIV) |Intubation and Mechanical Ventilation
- ARDS is a systemic disease with acute hypoxia/systemic and multiorgan dysfunction.
- Seen as a manifestation of trauma, sepsis, tissue damage, other severe illnesses.
- Mild ARDS was once called acute lung injury.
- If PaO2 < 10 Kpa on FiO2 = 0.5 then equals 20 Kpa
- Can lead to fibroproliferative phase and lung fibrosis
- Type 1 RF without evidence of significant cardiac dysfunction.
- Loss of Type 2 pneumocytes. Pulmonary inflammation.
- Proteinaceous alveolar oedema
- Neutrophil sequestration in pulmonary capillaries.
- Increased capillary permeability and Protein-rich pulmonary oedema.
- Capillary leakage with flooding and collapse of alveoli.
- Stiff poorly compliant lungs depleted of surfactant with severely impaired gas exchange.
Berlin modifications to ARDS definition
- Severity increases as the ratio of arterial PO2/FiO2 falls.
- Acute onset (within 1 week of known clinical insult).
- Bilateral opacities on CXR/CT unexplained by other pathology.
- Pulmonary artery wedge pressure (PAWP) <18 mmHg.
- Ratio PaO2/FiO2 mild <40 kPa, moderate <26.6 kPa, severe <13.3 kPa.
- Seen in context of other severe illness and worsening PaO2 and CXR changes.
- Breathlessness, cyanosis, basal inspiratory crackles.
- Tachycardia, severe hypoxia in the context of critical illness.
- Burns and smoke inhalation, pneumonia, pneumonitis from aspiration
- High altitude, fat or air embolism, near drowning, O2 toxicity.
- Systemic: sepsis, trauma, eclampsia, acute pancreatitis, heroin, barbiturates
- Transfusion-associated lung injury, malignancies, cardiopulmonary bypass.
- Congestive cardiac failure
- Bilateral pneumonia (ventilator associated or community acquired)
- Alveolar haemorrhage (WG/Goodpastures syndrome)
- Acute interstitial pneumonia
- Acute eosinophilic pneumonia or hypersensitivity pneumonitis (need steroids)
- ABG: PaO2/FiO2=300 mmHg (40 kPa) consistent with ARDS if obtained on PEEP or CPAP> 5 cmH2O.
- FBC: anaemia, ↑ neutrophils.
- U&E: AKI may be seen, ↑ lactate, ↑ ↑ LFTs.
- CXR: bilateral opacities (oedema).
- Chest CT: bilateral opacities, ground glass appearance.
- Echo: normal LV function. Right heart catheter: PAWP <15-18 mmHg. Blood cultures: sepsis.
- Coagulopathy: DIC may develop with ↑ APTT, PT and ↓ platelets.
- Broncho- alveolar lavage may be useful if undefined infection.
- ABC, Treat cause. Death due to progressive multiorgan dysfunction.
- Ventilate if needed. Consider High FiO2 and CPAP.
- Mechanical ventilation for worsening PaO2/FiO2.
- Lung protective ventilation strategies have been developed.
- The aim is adequate gas exchange with minimal ventilator-induced lung injury.
- Ventilation and prone positioning may be advocated.
- Neuromuscular blockade for 48 h may help.
- Diuretics: consider for oedema to generate a negative fluid balance.
- Haemofiltration may be used.
- Inhaled NITRIC OXIDE may be tried as well as aerosolised surfactant and PROSTACYCLIN for refractory hypoxia.
- Steroids have no evidence base. A
- Antibiotics for sepsis or pneumonia.
- ECMO may be considered for refractory hypoxia.
- PTX, ventilator-associated pneumonia, multiple organ failure, pulmonary fibrosis, RF. Death 30-50%
- De Haro et al. (2013) ARDS: prevention and early recognition. Annals Int Care, 3:11. Ferguson et al. (2005) Development of a clinical definition for ARDS using the Delphi technique. J Crit Care, 20:147.