Study Notes on Acute Respiratory Distress Syndrome (ARDS)

ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS)

Definition

• Acute Respiratory Distress Syndrome (ARDS) is a severe condition characterized by acute onset of hypoxemia due to non-cardiogenic pulmonary edema.

Anatomic Alterations of the Lungs

• The pathological changes associated with ARDS include:

  • Interstitial and intra-alveolar edema and hemorrhage

  • Alveolar consolidation

  • Intra-alveolar hyaline membrane formation

  • Pulmonary surfactant deficiency or abnormality

  • Atelectasis

Historical Names for ARDS

• Other names previously used to identify ARDS include:

  • Adult hyaline membrane disease

  • Adult respiratory distress syndrome

  • Capillary leak syndrome

  • Congestion atelectasis

  • Da Nang lung (high incidence in Vietnam War)

  • Hemorrhagic pulmonary edema

  • Noncardiac pulmonary edema

  • Oxygen pneumonitis

  • Oxygen toxicity

  • Postnontraumatic pulmonary insufficiency

  • Postperfusion lung

  • Postpump lung

  • Posttraumatic pulmonary insufficiency

  • Shock lung syndrome

  • Stiff lung syndrome

  • Wet lung

  • White lung syndrome

Causes of ARDS

• The most common causes of ARDS include:

  • Sepsis

  • Aspiration

  • Central nervous system disease

  • Cardiopulmonary bypass

  • Disseminated intravascular coagulation (DIC)

  • Severe trauma

  • Fat or air emboli

  • Infections

  • Inhalation of toxins and irritants

  • Immunologic reactions

  • Massive blood transfusions

  • Nonthoracic trauma

  • Oxygen toxicity (prolonged exposure to FiO2 > 0.60)

  • Pulmonary ischemia

  • Radiation-induced lung injury

  • Shock (hypovolemia)

  • Burns

  • Thoracic trauma

Clinical Data

Physical Examination

• Vital Signs

  • Increased respiratory rate (tachypnea)

  • Increased heart rate (pulse)

  • Changes in blood pressure

  • Presence of substernal/intercostal retractions

  • Cyanosis

Chest Assessment Findings

• Dull percussion note

• Bronchial breath sounds

• Crackles

Oxygen Toxicity in ARDS

• Oxygen toxicity can lead to ARDS, especially in the following situation:

  • Inhalation of > 60% oxygen for a prolonged period.

Radiologic Findings

• Chest Radiograph may reveal:

  • Increased opacity

  • Ground glass appearance

Berlin Definition of ARDS

Classification Criteria

• All elements must be present as follows (refers to Box 28-3):

  • Cardiogenic pulmonary edema must be ruled out as a primary alternative; if identified, treatment must address the cardiac issue.

  • Mild ARDS: P/F Ratio > 200 mmHg but < 300 mmHg

  • Moderate ARDS: P/F Ratio > 100 mmHg

  • Severe ARDS: P/F Ratio < 100 mmHg

Oxygen Therapy Protocol

• Hypoxemia in ARDS is commonly due to:

  • Widespread alveolar consolidation

  • Atelectasis

  • Increased alveolar-capillary thickening

Lung Expansion Therapy Protocol

• Treatments include:

  • PEEP (Positive End-Expiratory Pressure)

  • CPAP (Continuous Positive Airway Pressure)

  • Both aim to offset consolidation and atelectasis.

Mechanical Ventilation Protocol

• If ARDS is suspected, the patient should be placed on invasive ventilation promptly.

  • Acceptable modes are either volume-limited or pressure-limited.

Common ARDS Mechanical Ventilation Strategies

• Employ low-tidal volumes and high respiratory rates:

  • Use 6 to 8 mL/kg for tidal volumes

  • Maintain ventilatory rates between 20 and 25 bpm

  • Rates may need to increase to 35 bpm in some cases.

  • Utilize PEEP and/or CPAP to counteract atelectasis.

  • Permissive hypercapnia is often permitted.

Therapeutic Goals of Low-Tidal Volume Ventilation

• Aims include:

  • Decrease high transpulmonary pressure

  • Reduce overdistention of the lungs

  • Minimize barotrauma

Medications Commonly Prescribed

• Antibiotics to address infectious causes

• Diuretics to manage fluid retention

Final Notes

• Ensure meticulous monitoring of P/F ratio and vital signs during management of ARDS to evaluate effectiveness of treatment and adjust as necessary for optimal patient care.