title: Regional tolerance to acute normovolemic hemodilution: evidence that the kidney may be at greatest risk.
abstract: OBJECTIVE
  To evaluate the regional tolerance to acute normovolemic hemodilution (ANH).
  
  
  METHODS
  Prospective animal study.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Nine anesthetized (isoflurane) dogs.
  
  
  METHODS
  Hematocrit reduced in 10% decrements using dextran-for-blood exchange until cardiac insufficiency observed.
  
  
  RESULTS
  Cardiac index (CI) was measured using thermodilution and regional blood flow (RBF) in myocardium, brain, spinal cord, kidney, liver, duodenum, pancreas, spleen, skeletal muscle, and skin with radioactive microspheres. Oxygen delivery (DO2) was calculated from the product of respective blood flow and arterial oxygen content. Systemic oxygen extraction (EO2) and oxygen consumption (VO2) were calculated. Increases in CI during ANH were inadequate to prevent decreases in systemic DO2; however, an increased systemic EO2 maintained VO2 during graded ANH to hematocrit<10%. In the myocardium, brain, and spinal cord, increases in RBF were sufficient to maintain DO2 across the entire range of hematocrits, but this was not the case in the other organs studied. Of note, renal DO2 first decreased at a hematocrit of 30% and was only 25% of baseline at a hematocrit of 10%.
  
  
  CONCLUSIONS
  During graded ANH, increases in RBF were sufficient to maintain DO2 in only the heart, brain, and spinal cord. The especially marked decrease in DO2 in the kidney, combined with previous physiologic studies demonstrating its inability to augment EO2, suggest that this organ may be the most at risk of hypoxic damage during ANH.
authors.affiliation: Department of Anesthesiology, Advocate Illinois Masonic Medical Center, Chicago, IL; Departments of Anesthesiology and of Physiology and Biophysics, University of Illinois College of Medicine, Chicago, IL. Electronic address: gcrystal@uic.edu.
authors.forename: George J
authors.initials: GJ
authors.lastname: Crystal
mesh_terms: D000818:Animals; D004285:Dogs; D005260:Female; D006400:Hematocrit / Q000379:methods; D006438:Hemodilution; D007668:Kidney / Q000503:physiopathology*; D008297:Male; D023421:Models, Animal; D010101:Oxygen Consumption / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology
keywords: blood conservation; canine model; hemodilution; oxygen transport; radioactive microspheres; regional blood flow