Can switching from a pressure trigger to a flow trigger in mechanically ventilated critically ill patients decrease the incidence of ineffective triggers?

Switching to Flow Trigger Reduces Ineffective Triggering

Yes, switching from pressure trigger to flow trigger decreases the incidence of ineffective triggers in mechanically ventilated patients, particularly in those with auto-PEEP or obstructive lung disease. 1, 2

Evidence-Based Rationale

Flow Trigger Superiority in Auto-PEEP

• Flow triggering should be used instead of pressure triggering in patients with auto-PEEP because pressure triggers worsen patient-ventilator asynchrony and increase the work of breathing required to initiate a breath. 1

• In patients with intrinsic PEEP, pressure triggering requires patients to generate sufficient negative pressure to overcome both the trigger threshold (-1 to -2 cmH₂O) AND the auto-PEEP pressure, which can range from 10-15 cmH₂O in severe cases. 1, 3

• Flow triggering systems are more sensitive to patient effort in the presence of auto-PEEP because they detect changes in the ventilator's bias flow rather than requiring pressure changes. 1

Clinical Trial Evidence

• A prospective study comparing flow waveform triggering versus traditional flow triggering (2 L/min) demonstrated that the flow waveform method was more sensitive to patient effort, resulting in less ineffective effort but a greater number of auto-triggerings. 2

• In a 2025 lung model study, the advanced flow trigger algorithm (IntelliSync+) resulted in significantly fewer ineffective efforts compared with standard flow trigger (1.5% vs 7.3% without leak, P=0.01; 3.0% vs 10.8% with leak, P=0.01). 4

• Pressure triggering failed to achieve 3 successfully triggered consecutive breaths in any simulated respiratory condition, demonstrating its fundamental inadequacy. 4

Trigger Delay Comparison

• Overall trigger delay time was significantly shorter with advanced flow triggering compared to standard flow trigger in normal lung models (81 ms vs 99 ms, P<0.001) and ARDS models (223 ms vs 334 ms, P<0.001). 4

• The simulated patient effort needed to trigger the ventilator was considerably less with flow waveform triggering than with standard flow triggering at controlled levels of dynamic hyperinflation. 2

Implementation Algorithm

Step 1: Identify High-Risk Patients

• Patients with COPD, asthma, or any obstructive lung disease 1, 5
• Patients receiving high minute ventilation 1
• Patients with measured auto-PEEP >5 cmH₂O 1, 3
• Patients with observed ineffective triggering on waveform analysis 6, 7

Step 2: Switch Trigger Type

• Change from pressure trigger to flow trigger immediately 1, 8
• Set flow trigger sensitivity to 1-2 L/min initially 3, 2
• If using advanced flow waveform algorithms (e.g., IntelliSync+), activate this feature 4

Step 3: Add External PEEP

• Apply external PEEP of 5 cmH₂O or less to offset intrinsic PEEP and reduce triggering effort 1, 3
• Never set external PEEP levels in excess of intrinsic PEEP, as this worsens hyperinflation and causes hemodynamic compromise 1, 8
• For COPD/obstructive disease specifically, use PEEP 3-5 cmH₂O 8

Step 4: Monitor for Auto-Triggering

• Flow triggers are highly sensitive and may cause auto-triggering from cardiogenic oscillations or circuit leaks 1, 2
• Observe pressure-time and flow-time scalars continuously after the switch 1, 8
• If auto-triggering occurs, slightly decrease flow trigger sensitivity (increase threshold to 3-4 L/min) 3

Critical Pitfalls to Avoid

• Do not continue using pressure triggering in patients with auto-PEEP or COPD, as this fundamentally increases work of breathing and ineffective efforts 1, 5

• Do not increase sedation as first-line management for apparent agitation before ruling out trigger asynchrony as the underlying cause 8, 6

• Do not set flow trigger too insensitively (>5 L/min), as this negates the benefit of switching from pressure trigger 3, 2

• Do not ignore waveform analysis after making the switch—visual confirmation of reduced ineffective efforts is essential 8, 6, 7

Expected Outcomes

• Reduced work of breathing during the triggering phase 2, 5
• Decreased incidence of ineffective triggering efforts 2, 4
• Improved patient-ventilator synchrony 1, 6
• Potential reduction in duration of mechanical ventilation, though this requires optimization of all ventilator parameters, not just trigger type 6, 7