Tonometry

Intragastric luminal tonometry in intensive care

Mark A. Hamilton, Dr and Monty G. Mythen, Dr

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Introduction

Gastrointestinal tonometry is an exciting step forward in the monitoring of organ perfusion. The technology although fairly new has already undergone a number of changes, not all without controversy and debate. Much of the early work involved saline tonometry and the calculation of gastric intramucosal pH (pHi). The technique demanded a high degree of familiarity to reproduce accurate results and was plagued with many technical difficulties. The development of automated air tonometry has eliminated many of these problems and has seen a switch to PCO2 gap from pHi in an attempt to find a better and more reliable marker of splanchnic hypoperfusion. The literature is not unsurprisingly still heavily based on pHi and saline tonometry.

It has been difficult to define normal values for pHi and PCO2 gap and to compare results across institutions. The development of automated air tonometers (using air as the equilibrating medium) such as the TONOCAP have helped this transition and it is likely they will be the reference method for the foreseeable future. This review will outline the background to tonometry and present some of the evidence for its use in intensive care and major surgery. There will also be some discussion on the surrounding controversies of tonometry use.

Last updated: 1 September 2000
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