title: Alterations in renal microcirculation during cardiopulmonary bypass.
abstract: BACKGROUND
  This study was designed to investigate renal microvascular changes during cardiopulmonary bypass.
  
  
  METHODS
  Kidneys were harvested from each of four groups of 6 pigs. Group A were anesthetized and heparinized only. The remaining three groups underwent cardiopulmonary bypass at 28 degrees C, group B for 30 minutes and groups C and D for 120 minutes; group D had an additional 30 minutes of normothermic perfusion at the end of the experiment. Renal cortical blood flow was measured using radiolabeled microspheres. Microvascular morphology was defined by corrosion casting and scanning electron microscopy.
  
  
  RESULTS
  In group A, renal vascular resistance was 61+/-5.1 mm Hg x mL(-1) x min(-1). This value decreased to 28+/-7.8 in group B and 25+/-4.0 in group C (p < 0.05), and increased in group D to 40+/-4.1 (p < 0.05 versus groups A, B, and C). Cortical thickness, as measured by microvascular casts in groups A, B, and C, was 33, 34, and 31 mm, respectively, with equal distribution of the resin to the superficial and deep cortex but was significantly reduced in group D to 22 mm (p < 0.05 versus groups A, B, and C), with failure of the resin to fill the superficial cortical layer. Diameters of glomeruli as seen on the casts were 111+/-10.38 microm in group A, 100+/-9.24 microm in group B, and 82+/-4.4 microm in group C (p < 0.05 group A versus group C). The glomeruli from group D were still significantly smaller than group A (93+/-10.35 microm, p < 0.05). Mean glomerular capillary diameters were 4.65+/-0.26 microm in group A, 3.9+/-0.16 microm in group B, 3.6+/-0.19 microm in group C, and 3.65+/-0.3 microm in group D (p < 0.05 group A versus groups B, C, and D).
  
  
  CONCLUSIONS
  Hypothermic nonpulsatile cardiopulmonary bypass decreased renal vascular resistance, but the superficial and deep layers of the cortex were perfused equally. Glomeruli were reduced in size because of capillary narrowing. This was consistent with diversion of blood through bypass channels. With restoration of normothermia, underperfusion of the superficial cortex occurred, with potential for damage to these nephrons during the increased metabolic demands of rewarming.
authors.affiliation: Department of Cardiac Surgery, Royal Infirmary, Glasgow, Scotland.
authors.forename: V L
authors.initials: VL
authors.lastname: Pathi
authors.forename: J
authors.initials: J
authors.lastname: Morrison
authors.forename: A
authors.initials: A
authors.lastname: MacPhaden
authors.forename: W
authors.initials: W
authors.lastname: Martin
authors.forename: A M
authors.initials: AM
authors.lastname: McQuiston
authors.forename: D J
authors.initials: DJ
authors.lastname: Wheatley
mesh_terms: D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation / Q000008:administration & dosage; D000818:Animals; D000925:Anticoagulants / Q000627:therapeutic use; D001831:Body Temperature; D002196:Capillaries / Q000648:ultrastructure; D002315:Cardiopulmonary Bypass; D016319:Corrosion Casting; D004734:Energy Metabolism; D006493:Heparin / Q000627:therapeutic use; D007036:Hypothermia, Induced; D007530:Isoflurane / Q000008:administration & dosage; D007668:Kidney / Q000098:blood supply / Q000648:ultrastructure; D007672:Kidney Cortex / Q000098:blood supply / Q000648:ultrastructure; D007678:Kidney Glomerulus / Q000098:blood supply / Q000648:ultrastructure; D020366:Methylmethacrylate; D008768:Methylmethacrylates; D008833:Microcirculation / Q000502:physiology / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D008863:Microspheres; D009399:Nephrons / Q000098:blood supply / Q000648:ultrastructure; D019275:Radiopharmaceuticals; D012079:Renal Circulation / Q000502:physiology*; D017694:Rewarming; D013552:Swine; D013997:Time Factors; D014655:Vascular Resistance
chemical_list: D018685:Anesthetics, Inhalation; D000925:Anticoagulants; D008768:Methylmethacrylates; D019275:Radiopharmaceuticals; D020366:Methylmethacrylate; D006493:Heparin; D007530:Isoflurane