Pressure vs Time Graph

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)