Interpretation of Changes in Regional and Mucosal PCO2 Gradients: The Haldane Effect

  • S. M. Jakob
  • J. Takala
Conference paper
Part of the Yearbook of Intensive Care and Emergency Medicine book series (YEARBOOK, volume 2000)


The basis for gastrointestinal tonometry was published in 1964 [1]. In the 1980s saline tonometry for the assessment of the adequacy of local gastrointestinal perfusion was introduced in clinical practice, and since then, the technique has been developed further towards semi-continuous automated air tonometry. In order to link the measurement with a clinically used physiologic variable for the assessment of the adequacy of the perfusion, the calculated intramucosal pH (pHi) rather than the measured PCO2 was reported in most of the early trials. For the calculation of the pHi the Henderson-Hasselbalch equation was used, and it was assumed that the mucosal bicarbonate would equal the arterial bicarbonate. This assumption has produced substantial debate [2]. Nevertheless, pHi on intensive care admission has been found to be related to outcome in several trials [3–8]. The results from trials investigating the predictive value of gastric mucosal acidosis after an initial period of treatment in the intensive care unit (ICU) have been conflicting, demonstrating both a strong [7] and an absent relationship [9]. The association between increasing mucosal-arterial PCO2 gradients or mucosal acidosis and gastrointestinal hypoperfusion have been demonstrated both in animal experiments [10] and in human trials [11]. However, the effect of therapeutic interventions aiming to improve gastric mucosal acidosis or increase mucosal-arterial PCO2 gradients have produced conflicting results: While peri-operative volume loading seems to increase gastric pHi [12], we have reported worsening gastric mucosal acidosis in patients treated with various vasoactive drugs despite an increased total splanchnic blood flow [13,14]. Moreover, a dissociation between the assessment of mucosal perfusion using laser Doppler flowmetry or spectrophotometry and gastric tonometry, both during rewarming after cardiac surgery (Thorén A et al., unpublished data) and in response to vasoactive treatment [15] have been found.


Intensive Care Admission Gastric Tonometry Haldane Effect Mucosal Acidosis Vasoactive Treatment 
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© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • S. M. Jakob
  • J. Takala

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