Overview
Definition:
Acute Respiratory Distress Syndrome (ARDS) is a severe, acute lung injury characterized by diffuse alveolar damage leading to refractory hypoxemia, pulmonary edema, and decreased lung compliance
In pediatrics, ARDS is a life-threatening condition requiring aggressive management, often including rescue therapies when conventional mechanical ventilation fails.
Epidemiology:
Pediatric ARDS incidence varies widely by definition and patient population, estimated between 1.5 to 3.5 per 100,000 children annually
Risk factors include sepsis, pneumonia, aspiration, trauma, and near-drowning
Mortality rates remain significant, ranging from 20% to 50%, and are higher in neonates and infants.
Clinical Significance:
ARDS in children presents a significant challenge due to their smaller airways, different lung physiology, and evolving immune responses
Effective management of refractory hypoxemia and lung protection is paramount
Rescue therapies like inhaled nitric oxide (iNO) and High-Frequency Oscillatory Ventilation (HFOV) are employed to improve oxygenation and reduce ventilator-induced lung injury (VILI) in severe cases, directly impacting patient outcomes and survival.
Age Considerations
Neonatal ARDS:
Neonatal ARDS, often secondary to surfactant deficiency or perinatal insults, has unique pathophysiology and requires specialized ventilation strategies
Bronchopulmonary dysplasia (BPD) is a common sequela, influencing long-term respiratory health.
Infantile ARDS:
Infants with ARDS present with smaller tidal volumes and higher respiratory rates
Lung recruitment strategies and careful ventilator settings are crucial to avoid barotrauma and volutrauma
The underlying causes can be diverse, including viral infections and congenital anomalies.
Older Children:
In older children, ARDS is more commonly triggered by severe sepsis, pneumonia, or trauma
The lung architecture is more developed, but the inflammatory response can still lead to diffuse alveolar damage
The use of rescue therapies is guided by similar principles as in younger children, but lung mechanics can differ.
Clinical Presentation
Symptoms:
Rapid onset of severe dyspnea
Progressive tachypnea
Accessory muscle use
Grunting respirations
Retractions
Cyanosis
Cough (often non-productive initially)
Fever (if infectious etiology)
Decreased activity level.
Signs:
Tachycardia
Marked tachypnea
Severe hypoxemia refractory to conventional oxygen therapy
Diffuse crackles on auscultation
Reduced breath sounds
Pulsus paradoxus may be present
Hypotension (indicating shock)
Altered mental status.
Diagnostic Criteria:
Pediatric ARDS consensus criteria (e.g., Pediatric Acute Lung Injury Consensus Conference - PALICC) typically include: 1
Acute onset
2
Bilateral opacities on chest imaging not fully explained by effusions, lobar/lung collapse, or nodules
3
Respiratory failure not fully explained by cardiac dysfunction or fluid overload
4
Moderate to severe hypoxemia defined by PaO2/FiO2 ratio < 300 mmHg (in pediatrics, often adjusted for age and severity, e.g., PaO2/FiO2 < 15-20 kPa or SaO2 < 85% on FiO2 1.0)
Presence of risk factors for ARDS.
Diagnostic Approach
History Taking:
Detailed history of underlying conditions (e.g., sepsis, pneumonia, aspiration)
Timeline of symptom onset and progression
Recent illnesses or exposures
Birth history for neonates
Known cardiac or renal disease
Medications
Prior respiratory issues
Allergies
Red flags: rapid deterioration, extreme dyspnea, cyanosis.
Physical Examination:
Complete cardiopulmonary examination
Assess for signs of respiratory distress (retractions, nasal flaring, grunting)
Evaluate for peripheral edema (fluid overload)
Assess neurological status and hydration
Monitor vital signs closely, including oxygen saturation and heart rate.
Investigations:
Arterial blood gas (ABG) analysis: essential for assessing oxygenation (PaO2/FiO2), ventilation (PaCO2), and acid-base status
Complete blood count (CBC) with differential: to identify infection or inflammation
Serum electrolytes, renal and liver function tests
Blood cultures: if sepsis suspected
Chest X-ray (CXR) and/or CT scan: to evaluate for bilateral infiltrates, pulmonary edema, or other parenchymal abnormalities
Echocardiogram: to rule out cardiac causes of pulmonary edema and assess cardiac function
Sputum Gram stain and culture (if productive cough)
Viral respiratory panel (nasopharyngeal swab)
Lactate levels: to assess tissue perfusion in sepsis.
Differential Diagnosis:
Congenital heart disease (e.g., VSD, PDA with pulmonary hypertension)
Pulmonary edema (cardiogenic vs
non-cardiogenic)
Pneumonia (severe bacterial or viral)
Meconium aspiration syndrome
Transient tachypnea of the newborn
Bronchiolitis (severe)
Sepsis with multi-organ dysfunction
Anaphylaxis
Drowning
Pulmonary hemorrhage.
Management
Initial Management:
Early recognition and prompt initiation of supportive care
Secure airway and provide mechanical ventilation
Address underlying cause (e.g., antibiotics for pneumonia/sepsis, fluid resuscitation for shock)
Maintain adequate oxygenation and ventilation
Hemodynamic support with intravenous fluids and vasopressors if needed
Sedation and analgesia to reduce oxygen consumption and ventilator dyssynchrony.
Mechanical Ventilation Strategies:
Lung protective ventilation is paramount: small tidal volumes (4-6 mL/kg predicted body weight), adequate positive end-expiratory pressure (PEEP) to maintain lung volume and prevent alveolar collapse, and adequate respiratory rate to manage CO2
Permissive hypercapnia may be employed to avoid excessive PEEP
Avoidance of ventilator-induced lung injury (VILI).
Rescue Therapies:
When conventional ventilation fails to maintain adequate oxygenation, rescue therapies are considered
These include: 1
Inhaled Nitric Oxide (iNO): A selective pulmonary vasodilator
Primarily used to improve oxygenation by redistributing blood flow to well-ventilated lung areas, reducing intrapulmonary shunting
Initial dose typically 5-20 ppm, titrated based on response
Contraindications include significant left heart dysfunction or synchronous ventilatory support issues
2
High-Frequency Oscillatory Ventilation (HFOV): A mode of ventilation that uses very small tidal volumes delivered at very high rates (e.g., 3-15 Hz) with a superimposed mean airway pressure
It aims to maintain open alveoli, minimize shear stress, and improve gas exchange
Often initiated with a high mean airway pressure (MAP) and amplitude, adjusted to achieve adequate ventilation and oxygenation
Key for recruitment and lung rest.
Other Rescue Strategies:
Prone positioning: improves V/Q matching by reducing dorsal lung compression and promoting ventral lung aeration
Extracorporeal Membrane Oxygenation (ECMO): considered in severe, refractory ARDS when other therapies fail, providing cardiopulmonary support and lung rest
Surfactant therapy: may be beneficial in specific causes of pediatric ARDS (e.g., meconium aspiration, surfactant deficiency), but its role in generalized ARDS is debated and less established than iNO or HFOV.
Complications
Early Complications:
Barotrauma/volutrauma leading to pneumothorax or pulmonary interstitial emphysema
Ventilator-associated pneumonia (VAP)
Pulmonary edema progression
Airway collapse
Hemodynamic instability
Renal failure
Multi-organ dysfunction.
Late Complications:
Bronchopulmonary dysplasia (BPD) in premature infants
Chronic lung disease of infancy
Neurodevelopmental impairment
Pulmonary fibrosis
Prolonged hospital stay and rehabilitation needs
Increased risk of respiratory infections in the future.
Prevention Strategies:
Strict adherence to lung-protective ventilation strategies
Judicious use of PEEP to maintain lung volume without overdistension
Early and aggressive treatment of underlying causes
Strict infection control measures to prevent VAP
Minimizing ventilator days through prompt weaning
Careful fluid management to avoid overload.
Prognosis
Factors Affecting Prognosis:
Severity of initial lung injury (PaO2/FiO2 ratio)
Presence of co-morbidities
Etiology of ARDS
Age of the patient (neonates and very young infants have worse prognosis)
Response to rescue therapies
Development of complications like VAP or pneumothorax.
Outcomes:
Mortality rates in pediatric ARDS remain significant
Survivors may experience short-term respiratory sequelae or long-term pulmonary issues
Neurodevelopmental outcomes can be affected in severe cases requiring prolonged ICU stay
Early and effective management, including appropriate use of rescue therapies, improves survival chances.
Follow Up:
Survivors of pediatric ARDS require long-term follow-up to monitor for pulmonary function deficits, growth and development, and neurocognitive outcomes
Pulmonary rehabilitation and regular respiratory assessments are essential
Screening for chronic lung disease and recurrent respiratory infections.
Key Points
Exam Focus:
Understand the definition and diagnostic criteria for pediatric ARDS
Differentiate between various rescue therapies: iNO (pulmonary vasodilator, improves oxygenation by reducing shunt) and HFOV (recruitment, lung rest, minimizing VILI)
Know indications and contraindications for iNO and HFOV
Recognize the importance of lung-protective ventilation strategies (low tidal volumes, PEEP)
Be aware of alternative rescue measures like prone positioning and ECMO.
Clinical Pearls:
iNO is most effective in ARDS with pulmonary hypertension
HFOV is beneficial for lung recruitment and stabilization in severe ARDS
Titrate iNO carefully to avoid methemoglobinemia and rebound pulmonary hypertension
Monitor CO2 clearance with HFOV
may need to adjust frequency or amplitude
Always consider the underlying cause and treat it aggressively
Prone positioning is a simple yet effective rescue measure, especially in conjunction with HFOV.
Common Mistakes:
Delaying mechanical ventilation or rescue therapies in severe hypoxemia
Using excessively high tidal volumes or pressures, leading to VILI
Inadequate PEEP leading to alveolar derecruitment
Failing to consider alternative diagnoses or underlying causes
Not appropriately weaning from mechanical ventilation or rescue support when feasible
Misinterpreting ABG values, especially in the context of permissive hypercapnia.