title: Gastric intramucosal pH: a noninvasive method for the indirect measurement of tissue oxygenation.
abstract: BACKGROUND
  Monitoring the adequacy of tissue oxygenation is an important goal in the care of the critically ill patient. Global alterations in tissue oxygenation are inferred from changes in systemic oxygen transport (defined as the product of cardiac output and arterial oxygen content) and total oxygen consumption. These parameters, however, cannot measure the level of oxygenation of specific tissue beds, in particular those that are first affected by hypoxia, such as the gastrointestinal tract and the kidneys.
  
  
  CONCLUSIONS
  Gastrointestinal tonometry is a new method for measuring the partial pressure of carbon dioxide of the gastrointestinal mucosa. This information can be used in conjunction with the arterial blood bicarbonate to calculate the pH of the mucosa. Mucosal acidosis correlates well with the onset of anaerobic metabolism in response to hypoxia or sepsis. This review discusses the basic principles of tonometry, the results of experimental and clinical studies, and the practical aspects related to the implementation and use of tonometers in patients in the critical care unit.
  
  
  CONCLUSIONS
  Gastrointestinal tonometry is a relatively noninvasive device that appears capable of measuring metabolic changes produced by hypoxia. Because of the sensitive nature of the gastrointestinal mucosa, these changes often occur well in advance of other, more common, indices of hypoxia. The use of the tonometer may become a routine procedure in the overall monitoring of critically ill patients.
authors.affiliation: Pulmonary and Critical Care Medicine Division, University of Texas Medical School, Houston.
authors.forename: C H
authors.initials: CH
authors.lastname: Clark
authors.forename: G
authors.initials: G
authors.lastname: Gutierrez
mesh_terms: D015308:Anaerobic Threshold; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000032:analysis* / Q000097:blood / Q000378:metabolism; D002302:Cardiac Output; D003422:Critical Care; D005753:Gastric Mucosa / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000097:blood / Q000175:diagnosis* / Q000378:metabolism; D007413:Intestinal Mucosa / Q000737:chemistry* / Q000378:metabolism; D007441:Intubation, Gastrointestinal / Q000295:instrumentation / Q000379:methods* / Q000451:nursing; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods* / Q000451:nursing; D009730:Nursing Assessment; D009737:Nursing Records; D015399:Nursing Research; D010100:Oxygen / Q000032:analysis* / Q000097:blood / Q000378:metabolism; D010101:Oxygen Consumption; D011237:Predictive Value of Tests; D011379:Prognosis; D015203:Reproducibility of Results; D012106:Research; D018805:Sepsis / Q000097:blood / Q000175:diagnosis* / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen