Monday, February 23, 2009

Waveform of the week: Auto-triggering

Auto-triggering is a condition in which the ventilator repeatedly triggers itself because the trigger threshold is set too sensitive. 

Auto-triggering is caused by flow distortions:
  • Water in the ventilator circuit.
  • Circuit leaks.
  • Chest tubes.
  • Endo-tracheal tube cuff leaks.
  • Cardiac oscillations (high cardiac output, or balloon pump). 

The above image demonstrates auto-triggering caused by a leak, by evidence of the volume waveform (highlighted) never returning to baseline. When no leaks are present the volume waveform will return to baseline. 

To determine if the auto-triggering is due to cardiac oscillations: 
  • Evaluate the ECG or SPO2 waveform, does the triggering match the waveforms?
  • Evaluate the Airway Occlusion Pressure @ 0.1 second (P.01) if the P.01 is zero & the measured frequency is greater than the set frequency the ventilator is auto-triggering. 
To prevent Auto-triggering
  • Minimize leaks.
  • Make the trigger threshold less sensitive.