Adult acute respiratory distress syndrome (ARDS)
Serious reaction to various forms of injuries to the lung = RLD
- Mortality rate = 30% – 85%.
ARDS can occur within 24 to 48 hours of an injury or attack of acute illness. In such a case the patient usually presents with shortness of breath, tachypnoea, and symptoms related to the underlying cause, i.e. shock.
- if PaO2:FiO2 < 300 mmHg (40 kPa) acute lung injury (ALI) is considered to be present
- o ALI (=diffuse injury): hypoxaemia, non-cardiogenic pulmonary oedema, reduced lung compliance, capillary leakage. Cause = sepsis.
- if PaO2:FiO2 < 200 mmHg (26.7 kPa) acute respiratory distress syndrome (ARDS) is considered to be present.
- An ABG and CXR allow formal diagnosis
Aetiology of ARDs:
- Mechanical ventilation
- Trauma (especially pulmonary contusion)
- Major surgery
- Massive transfusions
- Smoke inhalation
- Drug reaction or overdose
- Fat emboli and reperfusion pulmonary oedema after lung transplantation
- Pulmonary embolectomy
- ARDS = pneumonia, eosinophilic pneumonia, cryptogenic organizing pneumonia, acute fibrinous organizing pneumonia, and diffuse alveolar damage (DAD).
- Of these, the pathology most commonly associated with ARDS is DAD.
- DAD is characterized by a diffuse inflammation of lung parenchyma.
- The triggering insult to the parenchyma usually results in an initial release of cytokines and other inflammatory mediators, secreted by local epithelial and endothelial cells
- Neutrophils and some T-lymphocytes quickly migrate into the inflamed lung parynchema and contribute in the amplification of the phenomenon.
- ARDS can produce sepsis and SIRS, leading to shock and MOF… CYTOKINE STORM!
Treatment and management (conservative/medical/surgical)
- Mechanical ventilation is an essential part of the treatment of ARDS.
- Treatment of the underlying cause is imperative, as it tends to maintain the ARDS picture. This often is a form of ABx.
- Aside from the infectious complications arising from invasive ventilation with tracheal intubation, positive-pressure ventilation directly alters lung mechanics during ARDS. The result is higher mortality, i.e. through baro-trauma, when these techniques are used
- Other factors of management include: APRV (Airway Pressure Release Ventilation = CPAP) and ARDS / ALI
- Positive end-expiratory pressure
- Prone position
- Fluid management
- Corticosteroids: The initial regimen consists of methylprednisolone 2 mg/kg daily
- Nitric oxide
- Surfactant therapy
- Pulmonary complications of ARDS include:
- Pulmonary: barotrauma (volutrauma), pulmonary embolism, pulmonary fibrosis, ventilator-associated pneumonia