Overview

ARDS is a clinical syndrome of acute respiratory failure characterized by hypoxemia and bilateral pulmonary infiltrates that cannot be fully accounted for by heart failure or fluid overload.

• Sepsis (most common cause), e.g., secondary to trauma, infection or peritonitis

• Trauma

• Shock

• Massive transfusion

• Acute pancreatitis

• Hematopoietic stem cell transplantation

• Medication (e.g., salicylic acid, tricyclic antidepressants, bleomycin)

• Recreational drug overdose (e.g., cocaine)

• Pneumonia

• Aspiration

• Inhaled toxins

• Pulmonary contusion

• Inhalation injury (e.g., inhalation of hyperbaric oxygen)

• Drowning incidents

• Fat embolism (e.g., through blunt trauma)

• Amniotic fluid embolism (e.g., during labor)

• Lung transplantation

• Tissue damage (pulmonary or extrapulmonary) → release of inflammatory mediators (e.g., interleukin-1) → inflammatory reaction → migration of neutrophils into alveoli → excessive release of neutrophilic mediators (e.g., cytokines, proteases, reactive oxygen species) → injury to alveolar capillaries and endothelial cells (diffuse alveolar damage, DAD) leading to:

  • Exudative phase: excess fluid in interstitium and on alveolar surface → pulmonary edema with normal pulmonary capillary wedge pressure (noncardiogenic pulmonary edema) → decreased lung compliance and respiratory distress

  • Hyaline membrane formation: exudation of neutrophils and protein-rich fluid into the alveolar space → formation of alveolar hyaline membranes → impaired gas exchange → hypoxemia

    • Hypoxemia → compensation through hyperventilation → respiratory alkalosis

    • Hypoxemia → chronic hypoxic pulmonary vasoconstriction → pulmonary hypertension and right-to-left pulmonary shunt (increased shunt fraction)

    • Damage to type I and type II pneumocytes → decrease in surfactant → alveolar collapse → intrapulmonary shunting

  • Organizing phase (late stage): proliferation of type II pneumocytes and infiltration of fibroblasts → progressive interstitial fibrosis

• Acute dyspnea

• Tachypnea and tachycardia

• Cyanosis

• Diffuse crackles

• Fever, cough, and chest pain may also be present.