In breath triggering, what pressure threshold is commonly used to trigger inspiration?

• A. Flow trigger below baseline
• B. Time
• C. Pressure → 1 cm H2O
• D. Baseline variable

Answer: (C)

Breath triggering with pressure relies on detecting a small negative pressure created when the patient begins to inhale. The ventilator is set to respond when airway pressure drops a short distance below the baseline, typically about 1 cm H2O. This small threshold makes the trigger sensitive enough to pick up patient effort without causing false triggering from normal circuit fluctuations or leaks. If the threshold is too large in magnitude, it can require more patient effort or cause auto-triggering; if it’s too small, the ventilator might miss patient efforts. Flow triggering is a different method that uses a change in inspiratory flow rather than a pressure drop. Time-based triggering and baseline adjustments relate to other modes and not the pressure threshold used for triggering inspiration.