From the Guidelines
Acute Respiratory Distress Syndrome (ARDS) is a life-threatening lung condition characterized by widespread inflammation in the lungs that leads to fluid buildup in the air sacs, preventing adequate oxygen from reaching the bloodstream, as defined by the presence of acute arterial hypoxemia (PaO2/FiO2 ≤ 300 mmHg) with a minimum requirement of 5 cmH2O positive end-expiratory pressure (PEEP), plus the presence of bilateral radiographic opacities not entirely explained by cardiac failure or fluid overload 1.
Definition and Classification
ARDS is classified as mild (200 < PaO2/FiO2 ≤ 300 mmHg), moderate (100 < PaO2/FiO2 ≤ 200 mmHg) or severe (PaO2/FiO2 ≤ 100 mmHg) 1. The severity of ARDS is also classified according to the degree of hypoxemia (Pa O2/FIO2 ratio), with mutually exclusive categories of mild, moderate, and severe 1.
Pathophysiology and Clinical Presentation
The pathophysiology involves damage to the alveolar-capillary membrane, leading to increased permeability, protein-rich fluid leakage into alveoli, and formation of hyaline membranes that impair gas exchange. Patients with ARDS experience severe shortness of breath, rapid breathing, and low blood oxygen levels that usually require mechanical ventilation.
Treatment and Management
Treatment focuses on supportive care with lung-protective ventilation strategies using low tidal volumes and appropriate positive end-expiratory pressure (PEEP) to prevent further lung damage. The use of corticosteroids, venovenous extracorporeal membrane oxygenation, neuromuscular blocking agents, and positive end-expiratory pressure (PEEP) are recommended in the management of ARDS, with individual patient and illness characteristics factored into clinical decision making 1. Prone positioning for 12-16 hours daily is recommended for moderate to severe cases to improve oxygenation. Fluid management aims to minimize pulmonary edema while maintaining adequate organ perfusion.
Outcomes and Prognosis
ARDS has a mortality rate of 35-40%, with survivors often experiencing long-term pulmonary, cognitive, and psychological impairments 1. Approximately 25% of mechanically ventilated intensive care unit (ICU) patients have ARDS, and many patients with ARDS also have persistent morbidity after discharge 1.
From the Research
Definition and Overview of Acute Respiratory Distress Syndrome (ARDS)
- Acute Respiratory Distress Syndrome (ARDS) is a common complication associated with significant negative outcomes in critically ill patients 2.
- ARDS is a severe lung inflammatory disorder with a 30-50% mortality, and sepsis and pneumonia are the leading causes of ARDS 3.
- The syndrome is characterized by the onset of hypoxemia, tachypnea, and loss of lung compliance due to some stimulus 4.
Pathophysiology of ARDS
- The pathophysiology of ARDS involves pulmonary capillary endothelial cell permeability and fluid leakage into the pulmonary parenchyma, followed by neutrophils, cytokines, and an acute inflammatory response 3.
- Neutrophils play an important role in the development of pulmonary edema associated with acute lung injury or ARDS, and they express pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) 3.
Management and Treatment of ARDS
- The management of ARDS includes low tidal volume ventilation, positive end-expiratory pressure, and fluid management guidelines, which have improved outcomes for patients with ARDS 3, 4.
- Other therapeutic options for ARDS include prone positioning, extracorporeal membrane oxygenation (ECMO), corticosteroids, and inhaled pulmonary vasodilating agents (prostacyclins and nitric oxide) 2, 5, 4.
- The use of ECMO has been shown to be effective in severe cases of ARDS, and prone positioning has been shown to decrease ventilator days and days in the intensive care unit 3, 4.