Acute Respiratory Distress Syndrome (ARDS)
This is a review of the definition of ARDS, examples of causes, pathophysiology, diagnostic criteria, and treatment options such as lung protective ventilation.
ARDS is an inflammatory lung disease that is usually not a primary disease but rather a result of systemic inflammation caused by predisposing conditions. Some of these conditions include intracranial hypertension, blood product administration, catheter-associated infections, sepsis, pneumonia, pulmonary contusions, cardiopulmonary bypass, pancreatitis, amniotic fluid embolism, long bone fractures, etc.
The inflammatory injury is the result of activated neutrophils that adhere to the vascular endothelium of pulmonary capillaries. This creates leaky capillaries and fibrinous deposits into alveolar spaces. Overtime, the lungs undergo remodeling and become fibrotic.
The diagnostic criteria consists of 5 components. The first is an acute onset, with respiratory failure progressing as quickly as requiring mechanical ventilation within 48 hours of symptom onset. Second is the presence of a predisposing condition as described above. Third is having a chest x-ray that shows bilateral pulmonary infiltrates. Fourth is a PaO2 to FiO2 ratio (P:F) of less than 200. And fifth is ruling out a cardiogenic cause with a PCWP of < 18 mmHg and no evidence of elevated left atrium pressure.
The ultimate cure for ARDS is correcting the underlying disease causing systemic inflammation. However, during lung recovery, there are ventilation management techniques to reduce on-going lung injury. This is commonly referred to as lung protective ventilation. The overall goal is to keep a low tidal volume (4-6 ml/kg of predicted body weight), increased PEEP (5-8 cmH2O), and maintain an overall low plateau pressure less than 30 cmH2O. In order to avoid a respiratory acidosis, the respiratory rate may need to be increased as high as 35 breaths/minute.
ARDS can be a difficult disease process to treat and can involve further management including paralysis for vent synchrony, proning to improve V/Q mismatch, and ECMO as a bridge to potential lung transplant.
