Characterization of Cerebral Energetics and Brain pH by 31 P Spectroscopy after Graded Canine Cardiac Arrest and Bypass Reperfusion

Recovery of cerebral energy metabolism is used to indicate CNS viability after ischemia. This study utilized ³¹P nuclear magnetic resonance (NMR) spectroscopy to measure cerebral energy state and intracellular pH in dogs subjected to 8, 12, or 16 min of cardiac arrest and reperfusion using cardiopulmonary bypass. Spectra were obtained throughout ischemia and initial reperfusion and repeated at 30 and 144 h post ischemia. Neurologic deficit scoring was performed at 12 and 24 h post insult and then daily. High-energy phosphates were depleted by the end of all ischemic intervals. Recovery occurred within 60 min of reperfusion and persisted with no differences in the rate of return between groups (p > 0.05). Brain pH (pH_b) decreased by the end of ischemia in all groups (p < 0.0001). Neither the pH_b nadir nor its recovery differed between groups (p > 0.05). Although long-term neurologic outcome differed between groups, the spectra were similar. Assessment of cerebral energy state using ³¹P NMR spectroscopy does not appear to be a sensitive indicator of neurologic outcome after global ischemia in dogs. Return of high-energy phosphates may be a necessary but not sufficient condition for cerebral recovery after ischemia. The return of high-energy phosphates after a 16-min cardiac arrest, however, indicates a potential for neurological recovery.