title: Comparison of commonly used clinical indicators of hypovolaemia with gastrointestinal tonometry.
abstract: OBJECTIVE
  The gastrointestinal tonometer, which allows measurement of gastrointestinal mucosal CO2 and subsequent derivation of gut intramucosal pH (pHi), has been demonstrated to be a sensitive predictor of outcome following major surgery. Current theory suggests that the origin of the low pH may be hypovolaemia. This study was designed to compare the temporal sequence of changes in tonometric readings with invasive blood pressure, stroke volume, heart rate, lactate and arterial blood gas measurements during progressive haemorrhage.
  
  
  METHODS
  Observational healthy volunteer study.
  
  
  METHODS
  Intensive care unit at University College London Hospitals.
  
  
  METHODS
  Six healthy, medically qualified volunteers.
  
  
  METHODS
  After obtaining baseline measurements, the subjects were progressively bled 25% (range = 21-31%) of their blood volume over a period of 1 h in two approximately equal aliquots. Equilibration was allowed for 30 min following the bleed, after which further measurements were made and the blood was then retransfused over 30 min.
  
  
  RESULTS
  There was no consistent change in any of the haemodynamic variables other than gastric intramucosal CO2:arterial CO2 gap (PiCO2-PaCO2) after removal of the first aliquot of blood, although five of the six subjects also demonstrated a fall in pHi. After removal of the second aliquot of blood, PiCO2-PaCO2 gap and pHi continued to indicate a worsening gastric intramucosal acidosis; stroke volume, as measured by suprasternal Doppler, demonstrated a marked fall, while all other variables measured had not altered consistently or to such a degree as to elicit a clinical response or cause suspicion of a hypovolaemic state. On retransfusion, all variables returned towards baseline.
  
  
  CONCLUSIONS
  This study demonstrates the value of tonometry as an early monitor of hypovolaemia and highlights the shortcomings of other more commonly measured clinical variables.
authors.affiliation: University College London Hospitals, Department of Intensive Care, UK.
authors.forename: C
authors.initials: C
authors.lastname: Hamilton-Davies
authors.forename: M G
authors.initials: MG
authors.lastname: Mythen
authors.forename: J B
authors.initials: JB
authors.lastname: Salmon
authors.forename: D
authors.initials: D
authors.lastname: Jacobson
authors.forename: A
authors.initials: A
authors.lastname: Shukla
authors.forename: A R
authors.initials: AR
authors.lastname: Webb
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001794:Blood Pressure / Q000502:physiology; D001810:Blood Volume; D002245:Carbon Dioxide / Q000097:blood; D005753:Gastric Mucosa / Q000098:blood supply / Q000378:metabolism*; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000097:blood; D008297:Male; D008365:Manometry; D011237:Predictive Value of Tests; D012769:Shock / Q000503:physiopathology*; D013152:Splanchnic Circulation; D013318:Stroke Volume / Q000502:physiology
chemical_list: D007773:Lactates; D002245:Carbon Dioxide