title: Membrane microdialysis: Evaluation of a new method to assess splanchnic tissue metabolism.
abstract: OBJECTIVE
  Measuring peritoneal lactate concentrations could be useful for detecting splanchnic hypoperfusion. The aims of this study were to evaluate the properties of a new membrane-based microdialyzer in vitro and to assess the ability of the dialyzer to detect a clinically relevant decrease in splanchnic blood flow in vivo.
  
  
  METHODS
  A membrane-based microdialyzer was first validated in vitro. The same device was tested afterward in a randomized, controlled animal experiment.
  
  
  METHODS
  University experimental research laboratory.
  
  
  METHODS
  Twenty-four Landrace pigs of both genders.
  
  
  METHODS
  In vitro: Membrane microdialyzers were kept in warmed sodium lactate baths with lactate concentrations between 2 and 8 mmol/L for 10-120 mins, and microdialysis lactate concentrations were measured repeatedly (210 measurements). In vivo: An extracorporeal shunt with blood reservoir and roller pump was inserted between the proximal and distal abdominal aorta, and a microdialyzer was inserted intraperitoneally. In 12 animals, total splanchnic blood flow (measured by transit time ultrasound) was reduced by a median 43% (range, 13% to 72%) by activating the shunt; 12 animals served as controls.
  
  
  RESULTS
  In vitro: The fractional lactate recovery was 0.59 (0.32-0.83) after 60 mins and 0.82 (0.71-0.87) after 90 mins, with no further increase thereafter. At 60 and 90 mins, the fractional recovery was independent of the lactate concentration. In vivo: Abdominal blood flow reduction resulted in an increase in peritoneal microdialysis lactate concentration from 1.7 (0.3-3.8) mmol/L to 2.8 (1.3-6.2) mmol/L (p = .006). At the same time, mesenteric venous-arterial lactate gradient increased from 0.1 (-0.2-0.8) mmol/L to 0.3 (-0.3 -1.8) mmol/L (p = .032), and mesenteric venous-arterial Pco2 gradients increased from 12 (8-19) torr to 21 (11-54) torr (p = .005).
  
  
  CONCLUSIONS
  Peritoneal membrane microdialysis provides a method for the assessment of splanchnic ischemia, with potential for clinical application.
authors.affiliation: Clinic for Intensive Care Medicine, University Hospital of Bern (Inselspital), Bern, Switzerland.
authors.forename: Rafael
authors.initials: R
authors.lastname: Knuesel
authors.forename: Jukka
authors.initials: J
authors.lastname: Takala
authors.forename: Lukas
authors.initials: L
authors.lastname: Brander
authors.forename: Matthias
authors.initials: M
authors.lastname: Haenggi
authors.forename: Hendrik
authors.initials: H
authors.lastname: Bracht
authors.forename: Francesca
authors.initials: F
authors.lastname: Porta
authors.forename: Stephan M
authors.initials: SM
authors.lastname: Jakob
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007511:Ischemia / Q000175:diagnosis*; D019344:Lactic Acid / Q000378:metabolism; D016014:Linear Models; D008297:Male; D008365:Manometry; D017551:Microdialysis / Q000295:instrumentation* / Q000379:methods*; D010313:Partial Pressure; D010537:Peritoneum / Q000378:metabolism*; D011897:Random Allocation; D013152:Splanchnic Circulation; D013552:Swine
chemical_list: D002245:Carbon Dioxide; D019344:Lactic Acid