Acute respiratory distress syndrome

Acute Respiratory Distress Syndrome (ARDS) is a serious and life-threatening condition characterized by rapid, severe lung dysfunction, which is typically a response to systemic injury or illness, and not attributable to a primary lung disease. It can arise from various insults such as surgery, major trauma, sepsis, and aspiration of gastric contents. The hallmark of ARDS is widespread inflammation and injury in the lungs leading to impaired gas exchange and decreased oxygen levels in the blood (hypoxemia), causing acute respiratory failure.

ARDSSevere

Pathophysiology

The pathophysiology of ARDS involves damage to the alveolar-capillary membrane, resulting in increased permeability and the leakage of fluid into the alveoli (the small air sacs in the lungs where oxygen is exchanged for carbon dioxide). This process, known as pulmonary edema, leads to impaired gas exchange and eventually respiratory failure. It is typically accompanied by an intense inflammatory response in the lungs, involving various immune cells and inflammatory mediators.

Clinical Presentation

Patients with ARDS often present with rapid onset dyspnea (difficulty breathing), hypoxemia, and bilateral pulmonary infiltrates seen on chest imaging. These symptoms usually develop within a week of the inciting event or a known clinical insult. It's also common to see decreased lung compliance (lung stiffness) during mechanical ventilation. In addition to respiratory symptoms, patients may also exhibit symptoms related to the underlying cause of ARDS, such as sepsis or trauma.

Diagnosis

The diagnosis of ARDS is made based on clinical, radiographic, and oxygenation criteria, according to the Berlin definition of ARDS. These include:

The onset of symptoms within one week of a known clinical insult, or new or worsening respiratory symptoms.

Bilateral opacities on chest imaging, not fully explained by effusions, lobar or lung collapse, or nodules.

Respiratory failure not fully explained by heart failure or fluid overload.

Decreased oxygenation, defined by the ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2).

There are no specific lab tests for ARDS. Instead, the diagnosis is based on the clinical presentation and the exclusion of other causes of the patient's symptoms.

Management

Management of ARDS is largely supportive and involves treating the underlying cause, providing supportive care, and mitigating further lung injury. This often requires intensive care unit (ICU) admission. Treatment strategies include:

• Mechanical ventilation: The use of a ventilator may be necessary to maintain oxygenation and carbon dioxide removal. However, it is important to use lung protective ventilation strategies, which include low tidal volume ventilation and the application of positive end-expiratory pressure (PEEP), to minimize ventilator-induced lung injury.
• Prone positioning: This can improve oxygenation and may decrease mortality in severe ARDS patients. It involves turning the patient onto their stomach to allow better expansion of the dorsal lung regions, thereby improving oxygenation.
• Fluid management: Conservative fluid strategies may be beneficial to reduce the amount of lung water and improve lung function.
• Pharmacological treatments: This includes treating the underlying cause of ARDS (such as antibiotics for sepsis) and providing supportive therapies like sedation and neuromuscular blockers. There are no specific drugs for treating ARDS itself, although research is ongoing.
• Extracorporeal membrane oxygenation (ECMO): This technique, which oxygenates the blood outside of the body, may be considered for severe, refractory cases of ARDS.

Prognosis

The prognosis of ARDS is variable and depends on factors such as the patient's age, underlying health status, and the severity of ARDS. Despite advances in care, the mortality rate for ARDS remains high, ranging from 35% to 50%. Survivors of ARDS often face long-term consequences including physical, cognitive, and psychological impairments, collectively known as post-intensive care syndrome (PICS).

Prevention

While ARDS itself cannot be directly prevented due to its nature as a secondary response to other illnesses or injuries, efforts can be made to prevent conditions that might lead to ARDS, such as sepsis and pneumonia, or to minimize risk factors such as smoking and excessive alcohol use. In the hospital setting, strategies to prevent ventilator-associated pneumonia and implement lung-protective ventilation can also help prevent the onset of ARDS.

References

Acute respiratory distress syndrome Resources
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