Changes in cerebral oxygen consumption and high-energy phosphates during early recovery in hypoxic-ischemic piglets: a combined near-infrared and magnetic resonance spectroscopy study.

Near-infrared spectroscopy (NIRS) offers the ability to assess brain function at the bedside of critically ill neonates. Our group previously demonstrated a persistent reduction in the cerebral metabolic rate of oxygen (CMRO(2)) after hypoxia-ischemia (HI) in newborn piglets. The purpose of this current study was to determine the causes of this reduction by combining NIRS with magnetic resonance spectroscopy (MRS) to measure high-energy metabolites and diffusion-weighted imaging to measure cellular edema. Nine piglets were exposed to 30 min of HI and nine piglets served as controls. Proton and phosphorous MRS spectra, apparent diffusion coefficient (ADC) maps, and CMRO(2) measurements were collected periodically before and for 5.5 h after HI. A significant decrease in CMRO(2) (26 +/- 7%) was observed after HI. Incomplete recovery of nucleotide triphosphate concentration (8 +/- 3% <controls) and reduced ADC (16 +/- 5%) suggested mitochondrial dysfunction. However, CMRO(2) did not correlate with any metabolite concentration during the last 3 h of the recovery period, and no significant changes were found in phosphocreatine and lactate levels. Therefore, the CMRO(2) decrease is likely a combination of impaired mitochondrial function and reduced energy demands during the acute phase, which has been previously observed in the mature brain.