Episode Details

Acute Respiratory Failure (ARF) and Acute Respiratory Distress Syndrome (ARDS) are critical pulmonary conditions where gas exchange is insufficient to support systemic organs.

The 80/20 Core: Pathophysiology & Clinical Care

1. Classification of ARF ARF is a symptom of inadequate lung function, categorized into two types:

• Hypoxemic (Oxygenation Failure): PaO2​<60 mm Hg on room air. The core defect is inadequate O2​ exchange, caused by V/Q mismatch, shunt, diffusion impairment, or alveolar hypoventilation. Shunt is an extreme mismatch where alveoli fill with fluid, making O2​ therapy alone ineffective.
• Hypercapnic (Ventilatory Failure): PaCO2​>50 mm Hg with pH<7.35. It represents insufficient CO2​ removal. Primary causes include CNS depression, neuromuscular disease, chest wall abnormalities, or airway obstruction (COPD, severe asthma).

2. ARDS Pathophysiology & Phases ARDS is a progressive form of ARF triggered by direct or indirect lung injury. Its hallmark is refractory hypoxemia—unresponsive to supplemental oxygen. It progresses in three phases:

• Injury/Exudative (24–72 hours): Inflammatory mediators damage the membrane, causing edema. Alveolar type II cells are damaged, reducing surfactant, which causes collapse (atelectasis) and stiff lungs.
• Reparative/Proliferative (1–2 weeks): Fibroblasts and inflammatory cells infiltrate, increasing resistance, causing pulmonary hypertension and decreased compliance.
• Fibrotic/Late Phase: Diffuse scarring and remodeling further reduce gas exchange surface area, correlating with a poor prognosis.

3. Interprofessional Management Treatment focuses on treating causes, optimizing gas exchange, and avoiding complications:

• Ventilation Support: BiPAP decreases the work of breathing (WOB) in mild ARF. Severe ARDS requires low tidal volume (VT​) ventilation (4–8 mL/kg) to prevent barotrauma/volutrauma. This causes permissive hypercapnia (allowing PaCO2​ up to 60 mm Hg if pH≥7.30). High PEEP is applied to recruit collapsed alveoli.
• Prone Positioning: For severe ARDS with refractory hypoxemia; turning patients prone recruits dorsal alveoli, improving V/Q matching.
• Supportive Care: Corticosteroids reduce airway inflammation. Fluid management keeps patients "on the dry side" to minimize pulmonary edema. Enteral nutrition should begin within 24–48 hours to preserve respiratory muscle mass.