Pathophysiology of ARDS and SIRS

Etiology and Pathophysiology

• Acute Lung Injury (ALI) is characterized by non-cardiogenic pulmonary edema, reduced lung compliance, and refractory hypoxemia.
• Acute Respiratory Distress Syndrome (ARDS) is the most severe form of ALI, marked by inflammation and increased permeability.
• ARDS definition includes:
  • PaO2/FIO2 ratio < 200 mmHg
  • Bilateral lung infiltrates
  • Pulmonary Artery Occlusive Pressure < 18 mmHg
• Criteria for ARDS diagnosis involve acute onset lung injury, bilateral opacities, and respiratory failure not related to heart failure.

Systemic Inflammatory Response Syndrome (SIRS)

• SIRS results from an exaggerated host defense reaction to bodily insults or tissue damage.
• Commonly associated with bacterial infections and can arise from trauma, hypoxia, and other conditions.
• Manifestations include fever, tachycardia, tachypnea, and elevated white blood cell count.

Precipitating Causes of ARDS

• Direct pulmonary insults are caused by:
  • Aspiration, inhalation of toxic substances, pneumonia, and pulmonary contusion.
• Indirect insults stem from conditions such as sepsis, multiple trauma, burns, and anaphylaxis.

Pathophysiology of ARDS

• Damage to the alveolar-capillary membrane increases permeability, leading to fluid and protein accumulation in the alveoli.
• Ineffective surfactant results in alveolar collapse and ventilation/perfusion mismatch, worsening oxygenation despite increased oxygen supply.
• Lung healing may progress to fibrosis and scarring, obstructing gas exchange.

Stages of ARDS

• Phase 0: Injury stage (first 12 hours - subtle signs).
• Phase I: Early exudative phase (alveolar edema with cellular debris).
• Phase II: Proliferative phase (persistent endothelial damage).
• Phase III: Fibroproliferative phase (chronic ARDS with significant fibrosis).

Assessment

• Assessment should focus on neurologic status, respiratory function, and cardiovascular health.
• Neurologic signs: altered consciousness, restlessness, or lethargy.
• Respiratory indicators: dyspnea, tachypnea, cough with sputum, and chest X-ray changes.
• Cardiovascular signs: tachycardia, potential cardiac failure, and elevated pulmonary pressure.

Nursing Diagnoses

• Ineffective airway clearance.
• Impaired gas exchange.
• Ineffective breathing pattern.
• Decreased cardiac output and altered tissue perfusion.

Collaborative Management

• Airway management may involve endotracheal intubation and mechanical ventilation.
• Goals of mechanical ventilation include improving gas exchange and relieving respiratory distress while preventing atelectasis.
• Challenges include ventilator-induced lung injury, O2 toxicity, and hypotension due to positive pressure.

Advanced Management Techniques

• High-Frequency Jet Ventilation reduces peak airway pressure with small tidal volumes.
• Pressure-controlled ventilation adjusts the inspiratory/expiratory time ratio for consistent gas delivery.
• Super PEEP aims to maintain PaO2 while minimizing barotrauma and hypotension risks.

Additional Techniques

• Low tidal volume ventilation prevents normal lung overdistension.
• Permissive hypercapnia allows higher CO2 levels with minimal side effects.
• Pharmacologic support includes antioxidants to mitigate lung injury.

This quiz covers the key concepts of Acute Lung Injury (ALI), Acute Respiratory Distress Syndrome (ARDS), and the Systemic Inflammatory Response Syndrome (SIRS). It highlights the definitions, diagnostic criteria, and the various precipitating causes that lead to these conditions. Test your knowledge on the pathophysiology and etiology of these critical respiratory and systemic responses.