Gastric tonometry


  • a method of assessing regional hypoperfusion


  • modified NG tube with a silicone balloon 14.4cm from the tip
  • gastric mucosal CO2 equilibrates luminal CO2, which equilibrates with fluid or air in the balloon
  • CO2 is measured via an infra-red CO2 analyser
  • intramucosal pH is then calculated using the Henderson-Hasselbalch equation
  • goal was to achieve a intramucosal pH of > 7.3 but this relied on use of arterial HCO3- as a surrogate for mucosal HCO3
  • then point of monitoring is now the arterial-mucosal CO2 gap (normally 8-10mmHg)


  • splanchnic hypoperfusion occurs early in circulatory shock -> intramucosal hypercapnia and acidosis.




  • requires N/G tube
  • signal degradation by luminal contents (feed, blood)
  • feed must be stopped for 2 hours prior to measurement
  • inability to identify a clear hypoxic threshold (empiric goal = a CO2 gap of < 25mmHg)
  • a need to suppress luminal CO2 generation by HCl titration of duodenal bicarbonate
  • a lack of convincing evidence that tonometry guided therapy improves outcome

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with 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 completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. 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 litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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