PARDS

Diagnostic Criteria for Pediatric ARDS (PARDS)

• The diagnosis of PARDS is established using the Pediatric Acute Lung Injury Consensus Conference (PALICC) 2015 criteria,.

• Severity stratification based on invasive mechanical ventilation oxygenation criteria:
  • Mild PARDS: 4 $\le$ OI < 8 or 5 $\le$ OSI < 7.5.
  • Moderate PARDS: 8 $\le$ OI < 16 or 7.5 $\le$ OSI < 12.3.
  • Severe PARDS: OI $\ge$ 16 or OSI $\ge$ 12.3.
• Special criteria apply for cyanotic heart disease, chronic lung disease, and left ventricular dysfunction, where an acute deterioration in oxygenation not explained by the underlying disease confirms PARDS,.

Pathogenesis

• ARDS is a complex inflammatory disorder characterized by non-cardiogenic pulmonary edema and arterial hypoxemia refractory to oxygen therapy due to an intrapulmonary shunt,.
• The "Permeability Originated Obstructive Response" (POOR) hypothesis describes a vicious cycle of ventilator-induced lung injury (VILI) propagation.
• Exudation of proteinaceous edema fluid leads to the inactivation of surfactant, causing significant heterogeneity in alveoli and the development of "stress concentrators".
• The disease presents with alveolar collapse and protein-rich edema fluid in the acute phase (lasting 7-10 days) and progresses to fibrosing alveolitis in the chronic phase.

Clinical Features

• Patients typically present with severe, acute respiratory distress, including tachypnea, increased work of breathing, chest retractions, and the use of accessory muscles of respiration.
• Severe arterial hypoxemia resistant to standard oxygen therapy is a cardinal feature.

Laboratory and Imaging Findings

• Chest Radiography: Demonstrates rapidly progressive, diffuse, bilateral pulmonary infiltrates or new infiltrates consistent with parenchymal disease,.
• Blood Gas Analysis: Reveals severe hypoxemia (low PaO2), initially often accompanied by hypocapnia due to hyperventilation, which may progress to hypercapnia and acidosis as lung compliance worsens,.
• Biomarkers: Elevated soluble Triggering Receptor Expressed on Myeloid cells-1 (s-TREM-1), procalcitonin (PCT), copeptin, C-reactive protein (CRP), plasminogen activation inhibitor-1, and surfactant protein D can aid in diagnosis and prognosis.

Treatment and Ventilatory Strategies

General and Supportive Management

• Source Control: Early initiation of appropriate antibiotics for suspected sepsis or pneumonia.
• Fluid Management: A conservative fluid strategy (70% of maintenance fluids) is advised once hemodynamically stable, utilizing diuretics or continuous renal replacement therapy if needed to minimize pulmonary edema and capillary leak,.
• Transfusion: The trigger for packed RBC transfusion is typically a hemoglobin level of 7 g/dL in hemodynamically stable children without severe hypoxemia or cyanotic heart disease.
• Sedation and Paralysis: Targeted sedation to prevent patient-ventilator asynchrony. Neuromuscular blocking agents are recommended in moderate-severe ARDS to optimize oxygen delivery and prevent effort-induced lung injury.

Ventilatory Strategies

• The primary goal is to maintain adequate gas exchange while minimizing ventilator-induced lung injury (volutrauma and atelectrauma).

Rescue Therapies

• Prone Positioning: Improves oxygenation by recruiting dorsal (nondependent) atelectatic lung units, improving V/Q matching, and decreasing mechanical compression by the heart,.
• High-Frequency Oscillatory Ventilation (HFOV): Used as a rescue modality for refractory hypoxemia (e.g., Plateau pressure > 28 cm H2O). It combines high frequencies with very low tidal volumes to maintain a constant distending mean airway pressure in the safe zone,,.
• Inhaled Nitric Oxide (iNO): A potent pulmonary vasodilator that improves V/Q matching; utilized for temporary rescue or as a bridge to ECMO.
• Extracorporeal Membrane Oxygenation (ECMO): Indicated as a final rescue therapy when conventional and other advanced strategies have failed,.