ABSTRACT:To examine the effects of opioid and tissue-damaging procedures (TDPs) [i.e. procedures performed in the neonatal intensive care unit (NICU) known to result in pain, stress, and tissue damage] on brain metabolites, we reviewed the medical records of 28 asphyxiated term neonates (eight opioid-treated, 20 non-opioid treated) who had undergone magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (MRS) within the first month of life as well as eight newborns with no clinical findings of asphyxial injury. We found that lower creatine (Cr), myoinositol (Ins), and N-acetylaspartate (NAA)/choline (Cho) (p Յ 0.03) and higher Cho/Cr and glutamate/glutamine (Glx) Cr (p Յ 0.02) correlated with increased TDP incidence in the first 2 d of life (DOL). We also found that occipital gray matter (OGM) NAA/Cr was decreased (p ϭ 0.03) and lactate (Lac) was present in a significantly higher amount (40%; p ϭ 0.03) in non-opioid-treated neonates compared with opioid-treated neonates. Compared with controls, untreated neonates showed larger changes in more metabolites in basal ganglia (BG), thalami (TH), and OGM with greater significance than treated neonates. Our data suggest that TDPs affect spectral metabolites and that opioids do not cause harm in asphyxiated term neonates exposed to repetitive TDPs in the first 2-4 DOL and may provide a degree of neuroprotection. (Pediatr Res 61: 614-621, 2007) P erinatal asphyxia is a common cause of neonatal encephalopathy and frequently results in epilepsy, cerebral palsy, and other long-term neurodevelopmental disorders (1). A cascade of biochemical events take place after asphyxia resulting in changes in brain metabolites that can be monitored noninvasively using proton magnetic resonance spectroscopy (MRS). Noninvasive in vivo measurements of NAA, total Cr [Cr and phosphocreatine (PCr)], Cho-containing compounds, Ins, Glx, and Lac are possible (2). NAA, an amino acid found exclusively in the nervous system, serves primarily as a neuronal marker. Cr, measured as Cr plus PCr with proton MRS, is a bioenergetic marker and reflects the energy potential available to neurons and other cells. The Cho peak includes contributions mostly from phosphocholine and its products glycerophosphocholine and phosphatidylcholine, which are intermediates in phospholipid metabolism thought to be released during membrane disruption. Ins is a glial marker and an important osmolyte. Glutamate and immediately formed glutamine are the major neurotransmitters for brain excitatory function and are often reported in combination because high spin-coupling makes it difficult to measure them separately. The measurement of Glx provides information about neuronal and glial metabolism and interaction (2,3). Lac and its redox partner pyruvate are the terminal metabolites in glycolysis.We recently reported that asphyxiated term neonates treated with opioids for pain during the first week of life had significantly less brain injury as assessed by MRI scores as well as better long-term neurologic outc...