Setting Inspiratory Pressure and PEEP in Pressure-Controlled Mandatory Ventilation
Start with an inspiratory pressure of 15-20 cm H₂O and PEEP of 5 cm H₂O, then titrate to maintain plateau pressure <30 cm H₂O and tidal volumes of 6-8 mL/kg predicted body weight. 1, 2, 3
Initial Ventilator Settings
When initiating PC-MV, use these starting parameters:
Inspiratory Pressure: Set to achieve tidal volumes of 6-8 mL/kg predicted body weight (PBW) 1, 2, 3
- Males: PBW = 50 + 2.3 × (height in inches - 60)
- Females: PBW = 45.5 + 2.3 × (height in inches - 60)
PEEP: Begin at 5 cm H₂O minimum 2
- Zero PEEP (ZEEP) is explicitly not recommended 2
Respiratory Rate: 10-15 breaths/min for obstructive disease; 15-25 for restrictive disease 1
I:E Ratio: 1:2 to 1:4 for obstructive disease (allowing adequate expiratory time); 1:1 to 1:2 for restrictive disease 1
Critical Pressure Limits
The plateau pressure must remain below 30 cm H₂O - this is your hard ceiling and the trigger for implementing permissive hypercapnia 1, 4. This limit is strongly supported by ARDS literature demonstrating reduced mortality when this threshold is respected.
Monitor driving pressure (plateau pressure minus PEEP), which should ideally be <15 cm H₂O, as this correlates better with outcomes than plateau pressure alone 2, 3.
PEEP Titration Strategy
After initial settings, individualize PEEP based on the underlying pathophysiology:
For ARDS/Inflammatory Lung Disease:
- Increase PEEP incrementally (typically 6-10 cm H₂O range) to improve oxygenation and prevent alveolar collapse 2
- Higher PEEP helps recruit atelectatic lung and improves compliance 1
- Balance recruitment against overdistension risk
For Obstructive Disease (COPD/Asthma):
- Critical caveat: Setting PEEP greater than intrinsic PEEP (iPEEP) can be harmful 1
- Measure or estimate iPEEP first
- Set applied PEEP slightly below iPEEP to reduce work of breathing without causing hyperinflation
- Prioritize prolonged expiratory time over high PEEP 1
For Restrictive Disease (Neuromuscular/Chest Wall):
- Lower inspiratory pressures (10-15 cm H₂O) often sufficient for neuromuscular disease 1
- Higher pressures needed for chest wall deformity due to reduced compliance 1
- PEEP assists lung recruitment and corrects hypoxemia 1
Adjusting Inspiratory Pressure
Titrate inspiratory pressure based on:
- Tidal volume achieved: Target 6-8 mL/kg PBW 1, 2, 3
- Plateau pressure: Must stay <30 cm H₂O 1, 4
- Patient effort: In assist modes, pressure should provide adequate support without being excessive 1
- Driving pressure: Aim for <15 cm H₂O 2
If plateau pressure exceeds 30 cm H₂O despite reducing tidal volume to 4 mL/kg PBW, accept permissive hypercapnia with pH >7.2 1, 4.
Common Pitfalls to Avoid
- Don't use ZEEP: Always maintain at least 5 cm H₂O PEEP to prevent atelectasis 2
- Don't exceed 30 cm H₂O plateau pressure: This increases mortality 1, 4
- Don't set PEEP above iPEEP in obstructive disease: This worsens hyperinflation 1
- Don't chase normal blood gases: Accept permissive hypercapnia (pH >7.2) rather than risk barotrauma 1, 4
- Don't use excessive FiO₂: Target SpO₂ 88-92% in ARDS; hyperoxia may worsen outcomes 2
Monitoring Requirements
Continuously monitor:
- Plateau pressure (requires inspiratory pause >0.5 seconds) 1
- Driving pressure (Pplat - PEEP) 2, 3
- Dynamic compliance 2
- Tidal volume delivery 1, 2, 3
- Patient-ventilator synchrony 1
The evidence strongly supports that tidal volume gradient (difference between protective and traditional ventilation) correlates with mortality benefit - larger reductions in tidal volume show greater survival advantage 3. This underscores the importance of strict adherence to low tidal volume targets even when it requires accepting hypercapnia.