Read the pressure, flow and volume waveforms to spot auto-PEEP (expiratory flow not returning to zero), ineffective triggering, double triggering, and flow starvation, and fix each with a specific setting change.
At the bedside
Timed steps- 1
Flow-time curve
LookExpiratory flow should return to zero before the next breath. If not: auto-PEEP (air trapping).
- 2
Expiratory hold
MeasureTotal PEEP − set PEEP = intrinsic PEEP.
- 3
Ineffective triggering
SpotDips in pressure or bumps in expiratory flow without a delivered breath: patient effort not sensed (auto-PEEP, over-assistance, weak effort). Fix: reduce PS or Vt, treat auto-PEEP, set external PEEP to ~70-80% of intrinsic PEEP in COPD, improve trigger.
- 4
Double triggering
SpotTwo breaths stacked with no full exhalation: patient demand exceeds set Ti or Vt. Fix: increase Ti or Vt carefully, or switch to PS/PC; consider sedation if Vt targets matter (ARDS).
- 5
Flow starvation
SpotScooped (concave) inspiratory pressure curve in volume control: increase flow or change to pressure mode.
- 6
Auto-triggering
SpotBreaths without effort: circuit leak, water in tubing, cardiac oscillations, too-sensitive trigger.
- 7
Reverse triggering
SpotDiaphragm contraction triggered by the passive breath in deeply sedated patients; may cause breath stacking.
Asynchrony: recognition and fix
| Type | Waveform clue | Fix |
|---|---|---|
| Ineffective trigger | Flow bump / pressure dip without a breath | Reduce PS/Vt, treat auto-PEEP, add PEEP (COPD), adjust trigger |
| Double trigger | Two breaths back-to-back | Increase Ti or Vt, change mode, review sedation |
| Flow starvation | Concave inspiratory pressure | Increase flow, pressure mode |
| Premature cycling | Expiratory flow spike after short breath | Lower cycle %, increase Ti |
| Delayed cycling | Pressure spike at end of inspiration | Raise cycle % (e.g. 40-50% in COPD) |
| Auto-trigger | Regular breaths without effort | Fix leak/water, reduce trigger sensitivity |
Patient fighting the ventilator
Step 1 of ~3
Decision: Hypoxaemic, hypotensive or distressed?
Based on Thille AW, Rodriguez P, Cabello B, Lellouche F, Brochard L. Educational use; follow local protocol.
Evidence
- Thille 2006: a quarter of patients had an asynchrony index > 10%; ineffective triggering was most common and linked with higher PS and longer ventilation.
🇮🇳 India notes
- Older ventilators may lack graphics; use clinical signs (accessory muscle use, chest movement not matching breaths) and ETCO2 waveforms.
References
Test yourself
Module quiz · score 70% to complete the module
Educational reference for trained clinicians. Check doses against your hospital protocol and the patient in front of you.