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Adult Respiratory Distress Syndrome

--Acute respiratory failure associated with pulmonary injury and characterized by noncardiogenic pulmonary edema, hypoxemia, and severe respiratory distress.

Causes and Incidence Adult respiratory distress syndrome (ARDS) is precipitated by a variety of acute processes that injure the lung. Trauma is the most common cause; others are anaphylaxis, aspiration of gastric reflux, pneumonia, inhalation burns from fire or chemicals, drug reactions, drug overdose, near-drowning, and oxygen toxicity. The condition may also develop as the result of an underlying disease process (e.g., leukemia, tuberculosis, pancreatitis, uremia, thrombocytopenic purpura) or as a byproduct of a medical procedure (e.g., coronary artery bypass, multiple blood transfusions, mechanical ventilation, hemodialysis).

The incidence and mortality are elusive, because ARDS is often misdiagnosed. Other names for ARDS include such names as shock lung, wet lung, stiff lung, white lung, Da Nang lung, or adult hyaline membrane disease. Recent studies place the survival rate at about 50% with treatment.

Disease Process The initial injury to the lung is poorly understood. It is hypothesized that activated WBCs and platelets accumulate in the capillaries, interstitium, and air spaces and release prostaglandins, oxygen radicals, proteolytic enzymes, and other products. These injure the cells, increase fibrosis, and reduce bronchomotor tone, leading to capillary leakage of blood and plasma into the interstitial and alveolar spaces. This results in alveolar flooding and reduced surfactant activity, producing atelectasis. Bronchial inflammation and proliferation of epithelial and interstitial cells follow. Collagen accumulates, resulting in severe interstitial fibrosis (stiff lung) with low lung compliance, reduced functional residual capacity (FRC), pulmonary hypertension, perfusion maldistribution, and hypoxemia.

Symptoms

Early

Dyspnea, particularly on exertion, followed by rapid, shallow respirations, inspirational chest retractions, and wheezing

Late

Bloody, sticky sputum; racing heart rate; clammy, mottled, cyanotic skin; severe difficulty breathing; confusion; coma

Potential Complications Complications include secondary bacterial superinfections, tension pneumothorax, multiple-system organ failure, metabolic and respiratory acidosis, and cardiac arrest.

Diagnostic Tests

Pulmonary function

Decreased FRC and compliance; low/normal pulmonary capillary web pressure; increased shunt fraction

Arterial blood gases

Decreased PaO2; low/normal PaCO2; elevated pH

Lactic acid

Elevated

Radiology

Blurred margins and alveolar infiltrates on early chest x-rays; normal cardiac silhouette

Treatments Mechanical ventilation with positive end-expiratory pressure and continuous positive airway pressure is generally required until the underlying problem has been identified and treated.

Surgery

None

Drugs

No specific drugs; morphine and pancuronium bromide (Pavulon) are used in the management of mechanical ventilation; antiinfective drugs may be used for underlying infections

General

Correction of underlying cause of injury; hyperalimentation to prevent nutritional depletion; blood gas monitoring to prevent oxygen toxicity; careful aseptic technique and monitoring of secretions to prevent superinfection; intubation and ventilation; tracheobronchial suctioning to clear secretions; cardiac monitoring; bed rest; fluid volume replacement; regulation of activity to reduce hypoxia; instruction in communicating with intubated patient; communication tools (e.g., alphabet or picture boards, response switches)