10.3 PARDS Lung-Protective Ventilation
Key Takeaways
- Start with physiologic tidal volume 6-8 mL/kg predicted body weight and reduce it when required to remain within pressure limits.
- PALICC-2 suggests plateau pressure no higher than 28 cm H2O when chest-wall compliance is normal (potentially higher when the chest wall is stiff). Track driving pressure, but the guideline does not establish a universal pediatric cutoff of 15 cm H2O.
- Gas-exchange targets and permissive hypercapnia must be individualized when neurocritical, cardiac, pulmonary vascular, or hemodynamic contraindications exist.
10.3 PARDS Lung-Protective Ventilation
The PARDS lung is heterogeneous: aeratable regions coexist with collapsed, flooded, or consolidated units. Ventilator settings must deliver adequate gas exchange without repeatedly overdistending the smaller functional lung or opening and closing unstable units. Treat the cause, reassess mechanics, and individualize support from the patient's pressure, volume, oxygenation, hemodynamic, and synchrony response.
Lung-Protective Conventional Ventilation
PALICC-2 suggests physiologic tidal volumes of 6 to 8 mL/kg, using predicted or ideal rather than edematous actual body weight. Use a smaller tidal volume when needed to stay within pressure limits; volumes below 4 mL/kg require caution because dead-space ventilation and severe dyssynchrony may increase.
Keep plateau pressure at or below 28 cm H2O when chest-wall compliance is normal. A limit up to 32 cm H2O may be considered when reduced chest-wall compliance makes airway pressure overestimate transpulmonary pressure. Track driving pressure under consistent measurement conditions and try to reduce excessive values, but PALICC-2 does not establish a universal pediatric cutoff. Select PEEP by oxygenation, compliance, recruitability, dead space, and hemodynamic response rather than a universal table alone.
Gas-exchange goals
- For mild/moderate PARDS, target SpO2 about 92%-97% while avoiding unnecessary FiO2.
- In severe PARDS after PEEP optimization, a saturation below 92% may be accepted; avoid prolonged values below 88% or above 97%.
- Permissive hypercapnia may be used to maintain lung protection when pH remains about 7.20 or higher, unless contraindicated by intracranial hypertension, severe pulmonary hypertension, selected congenital heart disease, hemodynamic instability, or another condition requiring tighter CO2 control.
- In traumatic brain injury with elevated ICP, restore normocapnia; brief mild hyperventilation is reserved as a bridge during impending herniation.
Monitoring the Protective Strategy
Measure plateau and driving pressure with appropriate inspiratory and expiratory holds when the patient and ventilator permit. Trend exhaled tidal volume, compliance, dead-space indicators, blood gases, oxygen requirement, and work of breathing. Look for a correctable cause when pressures rise: secretion, kink, bronchospasm, pneumothorax, abdominal hypertension, fluid overload, or worsening parenchymal disease. Deep sedation or neuromuscular blockade is not automatic; use the lowest level needed when synchrony cannot otherwise be achieved and monitor both benefit and harm.
Worked Ventilator Review
A child with predicted body weight 20 kg receives 140 mL exhaled tidal volume, or 7 mL/kg. Plateau pressure is 27 cm H2O and total PEEP is 10, giving a driving pressure of 17. Do not change one setting from the number alone. Verify that plateau and PEEP were measured under comparable passive conditions, examine chest-wall compliance, then consider reducing tidal volume, improving synchrony, or changing PEEP while tracking carbon dioxide, pH, recruitment, and circulation.
When lowering tidal volume raises PaCO2, first evaluate dead space and circuit burden. Remove unnecessary connectors, correct airway obstruction, treat fever and excessive metabolic demand, and ensure the set rate permits complete exhalation. If pH remains acceptable and no contraindication exists, permissive hypercapnia may be safer than increasing injurious pressure.
Hemodynamic interaction
PEEP can recruit lung and lower pulmonary vascular resistance, but excessive mean intrathoracic pressure can reduce venous return and right-ventricular output. After a PEEP change, reassess blood pressure, perfusion, lactate, urine output, ventricular function when available, compliance, and oxygenation. Improved saturation with worse systemic oxygen delivery is not a successful titration.
Synchrony and Sedation
Spontaneous effort can preserve diaphragm activity and dependent ventilation, yet excessive effort may generate large transpulmonary swings and patient self-inflicted lung injury. Correct pain, anxiety, fever, acidosis, flow starvation, trigger delay, and cycling mismatch before deepening sedation. If neuromuscular blockade is required to achieve protective goals, use the lowest effective dose with sedation, analgesia, eye care, pressure-injury prevention, and reassessment for discontinuation. Paralysis hides examination findings and work of breathing; it does not correct an inappropriate ventilator setup.
Pressure measurement trap
Peak pressure includes resistive and elastic loads; plateau pressure better approximates end-inspiratory alveolar pressure during no-flow conditions. A high peak with a stable plateau suggests increased resistance such as secretions, tube narrowing, bronchospasm, or excess flow. A rise in both peak and plateau suggests lower compliance or higher delivered volume. Treating every high peak by lowering tidal volume can miss a blocked tube, while treating every high pressure with bronchodilator can miss worsening parenchymal disease or pneumothorax.
Safety Cross-Check
After every ventilator change, reassess exhaled volume, pressure, synchrony, carbon dioxide, oxygenation, perfusion, and recruitment so improvement in one variable does not conceal harm in another.
An 8-year-old child with severe septic shock and PARDS has a predicted body weight (PBW) of 25 kg but an actual scale weight of 35 kg due to fluid overload from aggressive resuscitation. The patient is receiving volume-controlled ventilation. Current settings and measurements: tidal volume 250 mL, PEEP 10 cmH2O, peak inspiratory pressure (PIP) 34 cmH2O, and plateau pressure (Pplat) 29 cmH2O. An end-inspiratory pause confirms normal chest wall compliance. Arterial blood gas results show: pH 7.32, PaCO2 48 mmHg, PaO2 62 mmHg, and SpO2 90% on FiO2 0.80. Which of the following evaluations of the patient's ventilatory mechanics is correct, and what adjustment should the respiratory therapist recommend?
A 12-year-old pediatric patient with severe PARDS following a high-speed motor vehicle collision is being ventilated with a lung-protective low tidal volume strategy (5 mL/kg PBW). The arterial blood gas demonstrates: pH 7.24, PaCO2 64 mmHg, PaO2 68 mmHg, and HCO3- 26 mEq/L. The patient also sustained a severe closed traumatic brain injury with an indwelling intracranial pressure (ICP) monitor currently reading 24 mmHg (normal < 15–20 mmHg). What action must the respiratory care practitioner take regarding the ventilatory strategy?