PARDS

Diagnostic Criteria for Pediatric ARDS (PARDS)

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

Criterion	Definition
Age	Exclude patients with perinatal-related lung disease.
Timing	Onset within 7 days of a known clinical insult.
Origin of Edema	Respiratory failure not fully explained by cardiac failure or fluid overload.
Chest Imaging	Findings of new infiltrate(s) consistent with acute pulmonary parenchymal disease.
Oxygenation (Non-Invasive)	Full face-mask Bi-level ventilation or CPAP $\ge$ 5 cm H2O yielding a PaO2/FiO2 (PF) ratio $\le$ 300 or SpO2/FiO2 (SF) ratio $\le$ 264.
Oxygenation (Invasive)	Stratified using Oxygenation Index (OI) or Oxygen Saturation Index (OSI).

• 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).

Parameter	Strategy / Target
Tidal Volume (Vt)	3-6 mL/kg predicted body weight (PBW) for poor lung compliance; 5-8 mL/kg PBW for preserved compliance,.
Positive End-Expiratory Pressure (PEEP)	Titrated to optimize oxygenation and hemodynamics; often >10 cm H2O for severe ARDS,.
Plateau Pressure	Targeted $\le$ 28 cm H2O (allowing 29-32 cm H2O for patients with decreased chest wall compliance).
Permissive Hypoxemia	Target SpO2 92-97% (PEEP < 10 cm H2O) or 88-92% (PEEP $\ge$ 10 cm H2O),.
Permissive Hypercapnia	Accept elevated PaCO2 while maintaining pH $\ge$ 7.15 - 7.30 (unless contraindicated by intracranial hypertension or significant ventricular dysfunction).
Driving Pressure	Keep as low as possible (Plateau pressure - PEEP); an increase is strongly associated with mortality.

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,.