OVERVIEW
- volume control vs pressure control (see image here)
Information obtained
- peak inspiratory pressure
- plateau pressure
- compliance = gradient between PIP and Pplat (small = decreased)
- type of ventilation (volume vs pressure controlled)
- get a sense of flow rate
- CPAP level = pressure at beginning of inspiration
- patient triggering = negative deflection into CPAP just before inspiration
COMMON ABNORMALITIES
Normal
- normal PIP, Pplat, PTA (transairway pressure) and Ti (inspiratory time)
- pressure controlled ventilation shown below
High Raw
- raised PTA with increased airways resistance
High Flow
- inspiratory time short with high peak inspiratory pressure -> high inspiratory gas flow
Inadequate inspiratory flow
- scooped appearance to the synchronized breaths
Decreased Lung Compliance
- increased plateau pressure and increased PIP -> poor compliance
Auto PEEP (see images here)
- expiratory hold -> pressure-time waveform doesn’t return to base line
Dynamic Hyperinflation
- inspiratory hold -> plateau pressure > 25cmH20
Cardiac oscillations
- base line of pressure time wave forms moves up and down with the heart beat -> triggering synchronized breaths
Circuit leaks
- wave form drifts downwards (expired volume < inspired volume)
References and Links
Social media and web resources
- CCM tutorials — A system for analysing ventilator waveforms
- Drager — Curves and Loops in Mechanical Ventilation, Drager (pdf)
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