Acute lung injury (ALI) is a sudden onset of hypoxemia and diffuse pulmonary infiltrates, caused by direct lung injury or systemic conditions. ALI leads to inflammation and destruction of the alveolar-capillary membrane, causing capillary leakage, alveolar flooding, and decreased pulmonary surfactant. Symptoms include difficulty breathing, cyanosis, and hypoxemia. Treatment involves mechanical ventilation, supportive care, and treatment of the underlying cause. Chronic ARDS without infection may benefit from corticosteroids. Death is usually due to uncontrolled sepsis and multiple organ system failure.
Acute lung injury (ALI) is a condition characterized by the sudden onset of significant hypoxemia and the presence of diffuse pulmonary infiltrates as seen on chest radiographs, in the absence of heart failure. ALI is also called non-cardiogenic pulmonary edema due to the lack of associated cardiac abnormalities. Acute respiratory distress syndrome (ARDS) refers to severe ALI. The underlying mechanisms of acute lung injury and ARDS include increased permeability of blood vessels in the lungs, death of lung epithelial and endothelial cells, and inflammation. An ALI usually results from conditions that have caused direct types of injury to the lung or from systemic conditions, such as sepsis.
Both injury and systemic problems can cause ALI. Direct injuries that can lead to acute pulmonary injury include mechanical trauma to the chest, near drowning, fractures leading to medullary or fat embolism, burns, inhaled irritants, and ionizing radiation. Systemic conditions that can result in pulmonary injury include sepsis, disseminated intravascular coagulation, multiple blood transfusions, and severe allergic reactions. Most cases of ARDS occur among patients who have sepsis, gastric aspiration, widespread lung infections such as pneumonia, and head injuries and other bodily injuries due to trauma.
Despite differences in the underlying condition, cases of acute lung injury occur due to damage to endothelial and epithelial cells. Endothelium refers to the inner lining of the capillaries, while epithelium refers to the lining of the alveolar sacs. Normally these two layers form a barrier which keeps the alveolar-capillary membrane intact.
With the injury, an inflammatory response is triggered, leading to the release of various pro-inflammatory substances and the activation of inflammatory cells. This leads to destruction of the alveolar-capillary membrane, causing capillary leakage, alveolar flooding, decreased amount of pulmonary surfactant, and formation of hyaline membranes. These hyaline membranes form due to extravasation of protein-rich fluid that traps dead epithelial cells and are characteristic in the biopsy findings of an acute lung injury.
Symptoms that indicate an ALI are profound difficulty breathing or dyspnea, as well as increased respiratory rate or tachypnea. These symptoms are then followed by bluish discoloration of the skin and extremities called cyanosis. Measurement of blood gases and ventilation-perfusion ratios would show hypoxemia, respiratory insufficiency and low pulmonary compliance. Low blood oxygen or hypoxemia typically does not respond to oxygen therapy. On chest X-ray, both lungs have diffuse infiltrates, and parts may stiffen and collapse.
Treatment of this lung injury usually involves mechanical ventilation, supportive care, and treatment of the underlying cause. Cases of chronic ARDS without infection may benefit from corticosteroids. Death among patients who have acute lung injury is usually secondary to uncontrolled sepsis and multiple organ system failure.
Protect your devices with Threat Protection by NordVPN
