What strategies are important in preventing ventilator-induced lung injury in a pediatric patient with status asthmaticus and dynamic hyperinflation?

Preventing Ventilator-Induced Lung Injury in Pediatric Status Asthmaticus with Dynamic Hyperinflation

The most critical strategy is limiting plateau pressure to ≤30 cmH₂O while using low tidal volumes (≤10 mL/kg ideal body weight) and accepting permissive hypercapnia (PaCO₂ 45-60 mmHg, pH >7.20) to prevent worsening dynamic hyperinflation and barotrauma. 1, 2

Core Ventilator Settings to Prevent VILI

Pressure Limitation

• Keep plateau pressure ≤30 cmH₂O in obstructive airway disease to prevent barotrauma and worsening dynamic hyperinflation 1, 2
• Monitor plateau pressure continuously as increases typically reflect dynamic hyperinflation rather than decreased compliance in asthma patients 3
• A suggested upper limit for plateau pressure is 25-30 cmH₂O in severe asthma 3

Tidal Volume Strategy

• Target tidal volumes ≤10 mL/kg ideal body weight (not actual body weight) 1, 2
• Use physiologic tidal volumes and avoid exceeding 10 mL/kg ideal body weight 1
• Low tidal volumes reduce the risk of volutrauma and excessive lung inflation 4, 5

Permissive Hypercapnia

• Accept elevated PaCO₂ (45-60 mmHg) as long as pH remains >7.20 2
• Avoid rapid correction of hypercarbia and respiratory acidosis, as this requires high minute ventilation that worsens dynamic hyperinflation 4, 3
• Controlled hypoventilation with low tidal volume reduces barotrauma and hypotension risk 4

Respiratory Timing and Expiratory Management

Inspiratory and Expiratory Time

• Set inspiratory time and respiratory rate based on respiratory system mechanics (time constant = compliance × resistance) 1
• Prolong expiratory time to allow complete exhalation and prevent air-trapping 1, 4
• Use low ventilator rates to maximize expiratory time 3
• Avoid end-expiratory flow interruption to prevent air-trapping 1

Intrinsic PEEP Management

• Measure intrinsic PEEP (PEEPi) using an expiratory hold maneuver to guide ventilator adjustments 2, 3
• Set external PEEP lower than measured PEEPi 3
• Failing to measure intrinsic PEEP can result in inappropriate external PEEP settings 2

Critical Monitoring Parameters

Essential Measurements

• Monitor peak inspiratory pressure, plateau pressure, and mean airway pressure continuously 6, 2
• Monitor flow-time scalars continuously to detect incomplete exhalation and air-trapping 2
• Monitor pressure-time scalars 6
• Track arterial blood gases, SpO₂, and end-tidal CO₂ 6

Patient-Ventilator Synchrony

• Target optimal patient-ventilator synchrony to reduce work of breathing and prevent dyssynchrony that worsens dynamic hyperinflation 2
• Better synchrony improves patient comfort 1

Sedation and Neuromuscular Blockade

Controlled Mechanical Ventilation

• In severely ill children with obstructive airway disease requiring very high ventilator settings, use controlled mechanical ventilation (pressure or volume) with continuous sedation and/or muscle relaxants 1, 6
• Avoid paralytic agents unless respiratory function is extremely unstable, as they increase the risk of intensive care myopathy 7
• Caution is advised when using sedation and relaxation in the presence of cardiac dysfunction 1

Ventilator Modes and Strategies to Avoid

High-Frequency Ventilation Contraindications

• Avoid high-frequency jet ventilation (HFJV) in obstructive airway disease due to the risk of worsening dynamic hyperinflation 1, 2
• HFOV can be judiciously performed in obstructive airway disease but only with extreme caution and experience 1
• Unless very experienced with HFOV, the risk likely outweighs benefit in status asthmaticus 3

Manual Ventilation

• Avoid hand ventilation unless specific conditions dictate otherwise, as it often delivers excessive tidal volumes 2

Rescue Therapies When Conventional Ventilation Fails

ECMO Consideration

• Consider extracorporeal devices (ECMO) where available in reversible diseases if conventional ventilation fails 1, 6
• ECMO is particularly useful in cases of severe air-leak syndrome 3
• If no ECMO is available, early consultation of an ECMO center is recommended, as transporting patients who need ECMO can be hazardous 1

Common Pitfalls to Avoid

• Do not attempt rapid correction of blood gases with elevated minute ventilation, as this worsens dynamic hyperinflation and increases barotrauma risk 4, 3
• Do not use actual body weight for tidal volume calculations—always use predicted body weight 8
• Avoid excessive lung inflation by limiting minute ventilation despite consequent hypercapnia 7
• Intubation and mechanical ventilation should be avoided if at all possible, as underlying dynamic hyperinflation worsens with positive-pressure ventilation 4