CEREBRAL PROTECTION DURING MODERATE HYPOTHERMIC CIRCULATORY ARREST - HISTOPATHOLOGY AND MAGNETIC-RESONANCE SPECTROSCOPY OF BRAIN ENERGETICSAND INTRACELLULAR PH IN PIGS

Objective: We evaluated the effect of antegrade and retrograde brain p erfusion during moderate hypothermic circulatory arrest at 28 degrees C Methods: Phosphorus 31-magnetic resonance spectroscopy was used to f ollow brain energy metabolites and intracellular pH in pigs during 2 h ours of ischemia and 1 hour of reperfusion, Histopathologic analysis o f brain tissue fixed at the end of the experimental protocol was perfo rmed. Fourteen pigs were divided into two experimental groups subjecte d to antegrade (n = 6) or retrograde (n = 8) brain perfusion, Anesthes ia (n = 8) and hypothermic cardiopulmonary bypass groups (15 degrees C , n = 8) served as control subjects. In the antegrade and retrograde b rain perfusion groups, the initial bypass how rate was 60 to 100 ml . kg(-1). min(-1). In the antegrade group, the brain was perfused throug h the carotid arteries at a how rate of 180 to 210 ml . min(-1) during circulatory arrest at 28 degrees C. In the retrograde group, the brai n was perfused through the superior vena cava at a flow rate of 300 to 500 ml . min(-1) during circulatory arrest at 28 degrees C. Results: The intracellular pH was 7.1 +/- 0.1 and 7.2 +/- 0.1 in the anesthesia and hypothermic bypass groups, respectively, Brain intracellular pH a nd high-energy metabolites (adenosine triphosphate, phosphocreatine) d id not change during the course of the 3.5-hour study. In the antegrad e group, adenosine triphosphate and intracellular pH were unchanged th roughout the protocol. In the retrograde perfusion group, the intracel lular pH level decreased to 6.4 +/- 0.1, and adenosine triphosphate an d phosphocreatine levels decreased within the first 30 minutes of circ ulatory arrest and remained at low levels until the end of reperfusion . High-energy phosphates did not return to their initial levels during reperfusion, Histopathologic analysis of nine regions of the brain sh owed good preservation of cell structure in the anesthesia, hypothermi c bypass, and antegrade perfusion groups, The retrograde perfusion gro up showed changes in all the regions examined. Conclusions: The study shows that moderate hypothermic circulatory arrest at 28 degrees C wit h antegrade brain perfusion during circulatory arrest protects the bra in but that retrograde cerebral perfusion at 28 degrees C does not pro tect the brain.