Acute Respiratory Distress Syndrome (ARDS) Overview

Study Notes

Acute Respiratory Distress Syndrome (ARDS)

Overview

The term "acute respiratory distress syndrome" (ARDS) was first introduced in 1967 when medical professionals began to recognize the unique characteristics of a particular group of patients suffering from noncardiogenic pulmonary oedema, hypoxaemia, and the need for mechanical ventilation. These patients' conditions were not typically associated with heart failure, and their sudden onset suggested a distinct condition separate from other forms of respiratory distress. Since then, ARDS has remained a topic of intense study and concern among healthcare providers due to its high mortality rate and the challenges posed by its diagnosis and treatment.

ARDS was initially defined by a case-based report describing the noncardiogenic pulmonary oedema, reduced lung compliance, increased work of breathing, and the need for positive-pressure ventilation in association with various clinical disorders, such as pneumonia, sepsis, and aspiration. Later, an American-European consensus conference established specific diagnostic criteria for the syndrome in 1992, which were updated in 2012 with the so-called Berlin definition.

Today, ARDS is understood as a multifaceted syndrome characterized by dysregulated systemic inflammation, endothelial activation, and alveolar epithelial injury. It affects approximately 10% of patients in intensive care units (ICUs) globally and causes noncardiogenic pulmonary oedema, hypoxaemia, and the need for mechanical ventilation. Mortality rates remain high, averaging 30-40%, though these figures vary depending on the severity of the disease.

Symptoms

Patients with ARDS exhibit a range of symptoms related to respiratory failure. These include shortness of breath, reduced oxygen levels in the blood (hypoxaemia), increased work of breathing, and noncardiogenic pulmonary oedema. The severity of these symptoms can vary widely depending on individual factors such as underlying lung health and the specific cause of ARDS.

Causes

ARDS is most commonly associated with severe respiratory infections like pneumonia or influenza, but it can also be triggered by sepsis, aspiration of gastric contents, trauma, or other conditions that lead to widespread inflammation and damage within the lungs. In recent years, the COVID-19 pandemic has highlighted the potential for ARDS to arise from multiple causes, including various viruses, bacteria, and environmental factors.

Pathophysiology

The pathophysiological mechanisms behind ARDS are complex and involve dysregulated systemic inflammation, endothelial activation, and alveolar epithelial injury. This results in an accumulation of protein-rich inflammatory oedematous fluid in the alveolar space, which impairs gas exchange and leads to hypoxaemia. Treatment strategies focus on managing ventilation, providing sufficient oxygenation, and addressing underlying causes of lung damage.

Diagnosis

Diagnostic criteria for ARDS have evolved over time to reflect advances in our understanding of the condition. Currently, the Berlin definition requires several key features, including timing, imaging, origin, and oxygenation. Timing refers to the sudden onset of respiratory failure following a known clinical insult or new/worsening respiratory symptoms. Imaging should reveal bilateral opacities not fully explained by effusions, lobar/lung collapse, or nodules. Origin involves assessments to exclude hydrostatic edema if no risk factor exists, such as echocardiography. Oxygenation depends on partial pressure of arterial oxygen (PaO₂) and fraction of inspired oxygen (FiO₂), with mild ARDS defined as PaO₂/FiO₂ between 200 and 300 mmHg at positive end-expiratory pressures (PEEP) or continuous positive airway pressures (CPAP) of ≥ 5 cm H₂O.

Prevention and Management

Preventive measures for ARDS primarily focus on identifying patients at risk of developing the syndrome and implementing early interventions to mitigate lung damage. Potential preventative strategies include fluid management, early recognition and treatment of sepsis, and judicious use of mechanical ventilation. Once ARDS develops, supportive care remains the mainstay of treatment, with a range of therapies targeting different aspects of the disease process.

In recent years, research has explored novel treatments such as metabolomics profiling and mesenchymal stem cell transplantation, offering hope for improved outcomes in ARDS patients. However, more studies are needed to determine the long-term benefits of these approaches.

Long-Term Outcomes

Survivors of ARDS often face ongoing functional and psychological challenges, emphasizing the importance of recognizing the long-term consequences of this condition. As medical technology continues to advance and our understanding of ARDS deepens, researchers remain committed to improving both short-term survival rates and long-term quality of life for those affected by this devastating syndrome.

Description

Test your knowledge on Acute Respiratory Distress Syndrome (ARDS) with this quiz covering its history, symptoms, causes, pathophysiology, diagnosis, prevention, management, and long-term outcomes. Explore the complexities of this critical condition and learn about the evolving diagnostic criteria and treatment strategies.