title: A modified protocol for retrograde cerebral perfusion: magnetic resonance spectroscopy in pigs.
abstract: OBJECTIVE
  Retrograde cerebral perfusion (RCP) has been employed to protect the brain during cardiovascular surgery, requiring temporary hypothermic circulatory arrest (HCA). However, the protocol used for RCP remains to be modified if prolonged HCA is expected. The aim of this study was to determine the efficacy of a modified protocol for this purpose.
  
  
  METHODS
  After establishment of HCA at 15°C, 14 pigs were subjected to 90-min RCP using either the conventional protocol (i.e. alpha-stat strategy, 25-mmHg perfusion pressure and occluded inferior vena cava, Group I, n = 7) or the new protocol (i.e. pH-stat strategy, 40-mmHg perfusion pressure and unoccluded inferior vena cava, Group II, n = 7). After being rewarmed to 37°C, pigs were perfused for another 60 min. Phosphorus-31 magnetic resonance spectroscopy was used to track the changes of brain high-energy phosphates [i.e. adenosine triphosphate and phosphocreatine (PCr)] and intracellular pH (pHi). At the end, brain water content was measured.
  
  
  RESULTS
  During RCP, high-energy phosphates decreased in both groups, whereas adenosine triphosphate decreased much faster in Group I (10.4 ± 4.3 vs 30.4 ± 4.4% of the baseline, P = 0.007, 60-min RCP). After rewarming, the recovery of high-energy phosphates and pHi was much slower in Group I (PCr: 55.7 ± 9.1 vs 78.4 ± 5.1% of the baseline, P = 0.046; adenosine triphosphate: 26.6 ± 10.6 vs 64.8 ± 4.6% of the baseline, P = 0.007; pHi: 6.5 ± 0.4 vs 7.1 ± 0.1, P = 0.021 at 30-min normothermic perfusion after rewarming). Brain tissue water content was significantly higher in Group I (81.1 ± 0.4 vs 79.5 ± 0.4%, P = 0.016).
  
  
  CONCLUSIONS
  Application of the modified RCP protocol significantly improved cerebral energy conservation during HCA and accelerated energy recovery after rewarming.
authors.affiliation: Cardiac studies, Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, MB, Canada.
authors.forename: Yanmin
authors.initials: Y
authors.lastname: Yang
authors.forename: Luojia
authors.initials: L
authors.lastname: Yang
authors.forename: Jiankang
authors.initials: J
authors.lastname: Sun
authors.forename: Marco L
authors.initials: ML
authors.lastname: Gruwel
authors.forename: Roxanne
authors.initials: R
authors.lastname: Deslauriers
authors.forename: Jian
authors.initials: J
authors.lastname: Ye
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis / Q000737:chemistry; D000818:Animals; D001831:Body Temperature; D001923:Brain Chemistry / Q000502:physiology*; D002315:Cardiopulmonary Bypass / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D007036:Hypothermia, Induced; D008279:Magnetic Resonance Imaging / Q000379:methods*; D055420:Perfusion Imaging / Q000379:methods*; D010725:Phosphocreatine / Q000032:analysis / Q000737:chemistry; D010759:Phosphorus Isotopes / Q000032:analysis / Q000737:chemistry; D011897:Random Allocation; D013552:Swine
chemical_list: D010759:Phosphorus Isotopes; D010725:Phosphocreatine; D000255:Adenosine Triphosphate