Adult Acute Respiratory Distress Syndrome (ARDS)

16/06/2013 by admin | Respiratory

Adult acute respiratory distress syndrome (ARDS)

Definition

Serious reaction to various forms of injuries to the lung = RLD

Epidemiology

  1. 10/100,000/y
  2. Mortality rate = 30% – 85%.

 

Presenting complaint

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.

  1. if PaO2:FiO2 < 300 mmHg (40 kPa) acute lung injury (ALI) is considered to be present
    1. o ALI (=diffuse injury): hypoxaemia, non-cardiogenic pulmonary oedema, reduced lung compliance, capillary leakage. Cause = sepsis.
  2. if PaO2:FiO2 < 200 mmHg (26.7 kPa) acute respiratory distress syndrome (ARDS) is considered to be present.

 

Diagnostic tools/investigations

  1. An ABG and CXR allow formal diagnosis

 

Aetiology of ARDs:

  1. Mechanical ventilation
  2. Sepsis
  3. Pneumonia
  4. Shock
  5. Aspiration
  6. Trauma (especially pulmonary contusion)
  7. Major surgery
  8. Massive transfusions
  9. Smoke inhalation
  10. Drug reaction or overdose
  11. Fat emboli and reperfusion pulmonary oedema after lung transplantation
  12. Pulmonary embolectomy

 

Pathophysiology

  1. ARDS = pneumonia, eosinophilic pneumonia, cryptogenic organizing pneumonia, acute fibrinous organizing pneumonia, and diffuse alveolar damage (DAD).
  2. Of these, the pathology most commonly associated with ARDS is DAD.
  3. DAD is characterized by a diffuse inflammation of lung parenchyma.
  4. 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
  5. Neutrophils and some T-lymphocytes quickly migrate into the inflamed lung parynchema and contribute in the amplification of the phenomenon.
  6. ARDS can produce sepsis and SIRS, leading to shock and MOF… CYTOKINE STORM!

 

Treatment and management (conservative/medical/surgical)

  1. Mechanical ventilation is an essential part of the treatment of ARDS.
  2. Treatment of the underlying cause is imperative, as it tends to maintain the ARDS picture. This often is a form of ABx.

 

  1. 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
  2. Other factors of management include: APRV (Airway Pressure Release Ventilation = CPAP) and ARDS / ALI
  3. Positive end-expiratory pressure
  4. Prone position
  5. Fluid management
  6. Corticosteroids: The initial regimen consists of methylprednisolone 2 mg/kg daily
  7. Nitric oxide
  8. Surfactant therapy

 

Prognosis

  1. Pulmonary complications of ARDS include:
  2. Pulmonary: barotrauma (volutrauma), pulmonary embolism, pulmonary fibrosis, ventilator-associated pneumonia 
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