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Life in the Fast Lane • LITFL • Medical Blog

Emergency medicine and critical care medical education blog

Critical Care Compendium | Pressure vs Time Graph

Pressure vs Time Graph

by Chris Nickson, Last updated December 3, 2012

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

PIP versus Pplat

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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About Chris Nickson

FCICM FACEM BSc(Hons) BHB MBChB MClinEpid(ClinTox) DipPaeds DTM&H GCertClinSim

Chris is an Intensivist at the Alfred ICU in Melbourne and is an Adjunct Clinical Associate Professor at Monash University. He is also the Innovation Lead for the Australian Centre for Health Innovation and the Chair of the Australian and New Zealand Intensive Care Society (ANZICS) Education Committee. He has a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia's Northern Territory, Perth and Melbourne. He has since completed further training in emergency medicine, clinical toxicology, clinical epidemiology and health professional education. He coordinates the Alfred ICU's education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the 'Critically Ill Airway' course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of Lifeinthefastlane.com, the RAGE podcast, the Resuscitology course, and the SMACC conference. His one great achievement is being the father of two amazing children. On Twitter, he is @precordialthump.

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