Acute Respiratory Distress Syndrome (ARDS)

ARDS

- Rapid onset of noncardiac pulmonary edema
- Progressive refractory hypoxemia
- Extensive lung tissue inflammation
- Small blood vessel injury
- Multisystem organ malfunction
- Varied initial admitting diagnoses

ARDS patho

Acute lung injury from unregulated systemic inflammatory response to acute injury or inflammation
Damaged capillary membranes → plasma, blood cells leak into
interstitial space
 Damage to alveolar membrane → fluid enters alveoli
 Deficit of surfactant, increased alveolar surface tension, alveolar collapse with atelectasis
 Lungs become less compliant; gas exchange impaired
 Hyaline membranes form → further reduces gas exchange, compliance
 Fibrotic changes in lungs → less surface area for gas exchange
 Hypoxemia becomes resistant to improvement with supplemental O2
 PaCO2 rises→ Respiratory acidosis
 Significant hypoxemia→ metabolic acidosis develops → Multiple
Organ Dysfunction Syndrome (MODS)

ARDS etio

Nearly 200,000 Americans affected by ARDS each year
• Many more in 2020-2022 with COVID-19
• 90% of COVID-19 deaths attributed to ARDS
Affects all ages
• Increased incidence/severity amongst smokers
Mortality rate ranging from 25% to 45%
• Greater for men than women
• Greater for African Americans
• Patients who develop ARDS from sepsis have poorer outcomes than those who develop ARDS from pulmonary infections or trauma
• Why?

ARDS direct insults

• Pulmonary infections
• Viral or bacterial
• Aspiration of gastric contents
• Inhalation injuries
• Smoke inhalation
• Saltwater inhalation
• Drowning

ARDS indirect insults

• Sepsis
• Trauma
• Gastrointestinal (GI) infections
• Drug overdose
• Multiple blood transfusions
• Severe fluid overload

ARDS four stages 

Initiation of ARDS

Onset of pulmonary edema 

Alveolar collapse 

End-stage ARDS

ARDS manifestations and findings

As progressive respiratory distress develops:
- Intercostal retractions, use of accessory muscles
- Tachypnea as demand for O2 increases and patient tries to release
CO2
Adventitious lung sounds
- Edema?
- Atelectasis?
Chest x-ray shows interstitial changes, patchy infiltrates
- Late: Ground glass opacities and diffuse fluid
- Pulse oximetry, ABG levels show refractory hypoxemia
- Agitation, confusion, and lethargy

ARDS diagnostics

-ABG analysis to determine O2 levels in blood
-Chest x-ray or chest CT to assess fluid in lungs
-CBC, blood chemistry, and blood cultures to determine cause of ARDS
-Sputum culture

ARDS treatment

Oxygen!

No definitive drug therapy for ARDS

Nutrition support and delicate fluid management

Prone position

ECMO

Insertion of PA catheter to manage CO

Oxygen

• Intubation: May require atypical ventilator modes and high PEEP due to alveolar collapse and edema
• CPAP or BiPAP

Drug therapy for ARDS

• Vasoconstrictors to manage hemodynamics instability
• Diuretics
• Corticosteroids
• Bronchodilators
• NSAIDs
• Surfactant therapy
• ICU care may include sedation, paralytics and targeted temperature management to reduce oxygen demand

Prone position 

•Decreases dead space
• Reduces intrathoracic pressure and gravity forces on lung tissue
•Reduces atelectasis
•Enhances ventilation
•Improves V/Q matching
•Decreases mortality

ARDS complications

Ventilator-associated pneumonia (VAP)
Barotrauma & pneumothorax

PE or thrombosis

Decreased CO

GI effects

Lung transplant

Barotrauma & pneumothorax

• High PEEP pressures
• Decreased lung compliance

Decreased CO 

• Due to high PEEP
• Kidney and liver dysfunction

GI effects

• Gastric ulcers
• Distention