Brain metabolite levels assessed by lactate-edited MR spectroscopy in premature neonates with and without pentobarbital sedation

Abstract

Background and purpose: Pentobarbital is known to affect cerebral metabolism; pentobarbital sedation is, however, frequently used for MR imaging and MR spectroscopy, especially in children. Accurate assessment of the brain metabolite levels is important, particularly in neonates with suspected brain injury. We investigated whether pentobarbital sedation has any effect on the ratios of spectral metabolites lactate, N-acetylaspartate, or choline in a group of premature neonates.

Materials and methods: MR spectroscopy was performed in 43 premature neonates, all with normal concurrent MR imaging and normal neurodevelopmental outcome at 12 months of age. Of those neonates, 14 (33%) required pentobarbital (Nembutal 1 mg/kg) sedation during MR spectroscopy; the remaining 29 neonates did not receive any sedation. Ratios of lactate, choline, and N-acetylaspartate were calculated in the basal ganglia, thalami, and corticospinal tracts and compared between those neonates with and without sedation.

Results: Small amounts of brain lactate were detected in all of the premature neonates. The basal ganglia lactate/choline and lactate/N-acetylaspartate ratios were significantly lower, by 17% and 25% respectively, in the neonates with pentobarbital sedation compared with the age-matched neonates without sedation (P < .05). Sedation did not affect the lactate level in the thalami or the corticospinal tracts. The N-acetylaspartate/choline ratios were unaffected by pentobarbital sedation.

Conclusion: Pentobarbital sedation is associated with lower lactate/choline and lactate/N-acetylaspartate ratios in the basal ganglia of premature neonates, as determined by proton MR spectroscopy. Investigators should be aware of this phenomenon for accurate interpretation of their MR spectroscopy results.

Fig 1.

Location of the voxels and normal neonatal proton spectra obtained at a gestation age of 32 weeks from a prematurely born infant. The infant received pentobarbital sedation. A, The basal ganglion voxel includes the head of caudate and the anterior putamen (black box, left). The thalamic voxel is indicated by the white box in the left image. The corticospinal tract voxel includes the corticospinal tract within the centrum semiovale (white box, right). B, Lactate-edited spectra. Top row shows the summed spectra in each voxel for Cho, Cr, and NAA. The bottom row shows the difference spectra for each voxel; the difference spectra show only the Lac peaks. Cho indicates choline; Cr, creatine; Lac, lactate.