Overview
Definition:
Mechanical ventilation in pediatrics is the provision of ventilatory support to a child using a mechanical device to maintain adequate gas exchange when spontaneous breathing is insufficient
This involves setting specific parameters like tidal volume (VT) and positive end-expiratory pressure (PEEP) tailored to the child's physiology and clinical condition.
Epidemiology:
The need for mechanical ventilation in pediatrics arises in various conditions including severe respiratory distress syndrome, congenital anomalies, sepsis, trauma, and post-surgical recovery
Incidence varies significantly with age and underlying pathology, but it remains a critical intervention in pediatric intensive care units worldwide.
Clinical Significance:
Appropriate management of mechanical ventilation, particularly optimizing tidal volumes and PEEP, is crucial for preventing ventilator-associated lung injury (VALI), improving oxygenation, facilitating CO2 removal, and ultimately reducing morbidity and mortality in critically ill pediatric patients
Incorrect settings can lead to barotrauma, volutrauma, atelectrauma, and biotrauma.
Tidal Volume Targets
Rationale:
Tidal volume (VT) represents the amount of air delivered with each breath
In pediatrics, VT is typically set based on ideal body weight to minimize lung stress and strain
The goal is to achieve adequate ventilation while avoiding overdistension.
Target Ranges:
For most pediatric patients, a starting VT of 6-8 mL/kg of ideal body weight is recommended
In cases of acute lung injury (ALI) or acute respiratory distress syndrome (ARDS), a lower VT of 4-6 mL/kg may be considered to reduce driving pressure and lung injury.
Adjustments:
VT adjustments are guided by arterial blood gas (ABG) analysis, end-tidal CO2 (EtCO2) monitoring, and assessment of respiratory mechanics
If hypercapnia persists, VT may be increased cautiously, ensuring driving pressure remains within acceptable limits
Conversely, if air trapping or increased peak inspiratory pressure (PIP) is observed, VT may need to be reduced.
Peep Targets
Rationale:
Positive end-expiratory pressure (PEEP) is the pressure maintained in the airways at the end of expiration
It helps to keep alveoli open, improve oxygenation, reduce shunt, and prevent atelectasis.
Initial Peep Setting:
A starting PEEP of 5-8 cmH2O is commonly used in pediatric patients
For patients with ARDS, higher PEEP levels (e.g., 8-15 cmH2O or more) may be necessary to recruit alveoli and improve oxygenation, often guided by PEEP/FiO2 tables or lung recruitment maneuvers.
Optimization And Monitoring:
PEEP optimization aims to achieve adequate oxygenation without compromising hemodynamics or causing excessive lung injury
Monitoring includes oxygen saturation (SpO2), end-tidal CO2 (EtCO2), peak and plateau pressures, and assessment of chest wall mechanics
Frequent reassessment of PEEP is necessary as the patient's condition evolves
Permissive hypercapnia may be accepted to maintain lung-protective strategies.
Ventilator Modes And Settings
Common Modes:
Pressure control ventilation (PCV), volume control ventilation (VCV), synchronized intermittent mandatory ventilation (SIMV), and pressure support ventilation (PSV) are frequently used
Volume-assured pressure control (VAPC) offers a hybrid approach
The choice depends on the patient's condition and clinician preference.
Other Parameters:
In addition to VT and PEEP, other critical settings include respiratory rate (RR), FiO2, inspiratory time (Ti), and trigger sensitivity
RR is adjusted to maintain adequate CO2 clearance, typically 10-30 breaths/min for neonates and older children, or determined by patient's metabolic needs
FiO2 is titrated to achieve target SpO2 (90-95% generally, but may vary).
Adjuncts:
High-frequency oscillatory ventilation (HFOV) may be considered for severe ARDS or conditions where conventional ventilation fails
Lung recruitment maneuvers (e.g., sustained inflation) can be used to open collapsed alveoli before or during ventilation.
Monitoring And Assessment
Gas Exchange:
Arterial blood gases (ABGs) are essential for assessing oxygenation (PaO2), ventilation (PaCO2), and acid-base status
Non-invasive monitoring includes pulse oximetry (SpO2) and capnography (EtCO2).
Lung Mechanics:
Monitoring peak inspiratory pressure (PIP), plateau pressure (Pplat), driving pressure (ΔP = Pplat - PEEP), and compliance helps assess the stress on the lungs
High pressures or low compliance indicate potential lung injury or airway obstruction.
Hemodynamics:
Ventilation can affect hemodynamics by increasing intrathoracic pressure, which can reduce venous return and cardiac output
Hemodynamic monitoring (heart rate, blood pressure, central venous pressure) is crucial, especially in younger or unstable patients.
Complications Of Mechanical Ventilation
Lung Injury:
Ventilator-associated lung injury (VALI), including barotrauma (pneumothorax, pneumomediastinum), volutrauma (overdistension), atelectrauma (cyclic alveolar collapse and reopening), and biotrauma (inflammatory response).
Other Complications:
Ventilator-associated pneumonia (VAP), tracheal injury, vocal cord dysfunction, reintubation difficulties, and the impact on patient comfort and sedation requirements
Autonomic dysfunction and impaired diaphragmatic function can also occur with prolonged ventilation.
Key Points
Exam Focus:
Remember lung-protective ventilation strategies: low VT (4-8 mL/kg ideal body weight), appropriate PEEP to maintain alveolar recruitment, and limiting driving pressure (< 15-18 cmH2O)
Understand the goals of VT and PEEP in different pediatric respiratory conditions.
Clinical Pearls:
Always assess the child as a whole
ventilation is just one component
Titrate settings based on ABGs and lung mechanics, not just pre-set protocols
Use the lowest FiO2 and PEEP necessary to achieve target SpO2
Consider lung recruitment maneuvers cautiously when indicated.
Common Mistakes:
Using high tidal volumes in all pediatric patients without considering ideal body weight or lung pathology
Inadequate PEEP leading to atelectasis and hypoxemia
Over-reliance on FiO2 alone to correct hypoxemia without addressing ventilation or PEEP
Ignoring driving pressure as a measure of lung stress.