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Key Features

Essentials of Diagnosis

  • Onset of respiratory distress, often progressing to respiratory failure, within 7 days of a known clinical insult

  • New bilateral radiographic pulmonary opacities not explained by pleural effusion, atelectasis, or nodules

  • Respiratory failure not fully explained by heart failure or volume overload

  • Impaired oxygenation, with ratio of PaO2/FIO2 < 300 mm Hg, with positive end-expiratory pressure (PEEP) ≥ 5 cm H2O

General Considerations

  • Damage to capillary endothelial cells and alveolar epithelial cells is common and results in increased vascular permeability and decreased production and activity of surfactant, leading to

    • Interstitial and alveolar pulmonary edema

    • Alveolar collapse

    • Hypoxemia

  • Severity of ARDS is based on the level of oxygenation impairment

    • Mild: PaO2/FIO2 ratio of between 200 and 300 mm Hg

    • Moderate: PaO2/FIO2 ratio between 100 and 200 mm Hg

    • Severe: PaO2/FIO2 ratio less than 100 mm Hg

Systemic insults associated with ARDS

  • Sepsis (Table 9–28)

  • Shock

  • Pancreatitis

  • Multiple blood-product transfusions

  • Trauma

  • Burns

  • Disseminated intravascular coagulation (DIC) and thrombotic thrombocytopenia purpura (TTP)

  • Drugs

    • Opioids

    • Aspirin

    • Phenothiazines

    • Tricyclic antidepressants

    • Amiodarone

    • Chemotherapeutics

    • Nitrofurantoin

    • Protamine

  • Cardiopulmonary bypass

  • Head injury

  • Paraquat exposure

Table 9–28.Selected disorders associated with ARDS.
Pulmonary insults associated with ARDS

  • Aspiration of gastric contents

  • Near-drowning

  • Pneumonia, bacterial, viral, or fungal

  • Miliary tuberculosis

  • Toxic gas inhalation

    • Nitrogen dioxide

    • Chlorine

    • Sulfur dioxide

    • Ammonia

    • Smoke inhalation

  • Free-base cocaine smoking

  • Embolism of thrombus, fat, air, or amniotic fluid

  • Lung contusion

  • Acute eosinophilic pneumonia

  • Cryptogenic organizing pneumonia

  • Acute upper airway obstruction

  • Lung reexpansion or reperfusion

  • Lung contusion

  • Radiation exposure

  • High-altitude exposure

  • Oxygen toxicity

Clinical Findings

Symptoms and Signs

  • Rapid onset of profound dyspnea, usually 12–48 hours after the initiating event

  • Labored breathing and tachypnea, with crackles on examination

  • Marked hypoxemia refractory to supplemental oxygen

  • Multiple-organ failure in many patients

Differential Diagnosis

  • Because ARDS is a syndrome, the concept of differential diagnosis applies only in considering the precipitating illness or injury

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