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Near-infrared spectroscopy measurements of cerebral blood flow and oxygen consumption following hypoxia-ischemia in newborn piglets

¹Imaging Division, Lawson Health Research Institute, London, Ontario; ²Imaging Research Laboratories, Robarts Research Institute, London, Ontario; ³Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada

Submitted 12 July 2005 ; accepted in final form 17 November 2005

Impaired oxidative metabolism following hypoxia-ischemia (HI) is believed to be an early indicator of delayed brain injury. The cerebral metabolic rate of oxygen (CMRO₂) can be measured by combining near-infrared spectroscopy (NIRS) measurements of cerebral blood flow (CBF) and cerebral deoxy-hemoglobin concentration. The ability of NIRS to measure changes in CMRO₂ following HI was investigated in newborn piglets. Nine piglets were subjected to 30 min of HI by occluding both carotid arteries and reducing the fraction of inspired oxygen to 8%. An additional nine piglets served as sham-operated controls. Measurements of CBF, oxygen extraction fraction (OEF), and CMRO₂ were obtained at baseline and at 6 h after the HI insult. Of the three parameters, only CMRO₂ showed a persistent and significant change after HI. Five minutes after reoxygenation, there was a 28 ± 12% (mean ± SE) decrease in CMRO₂, a 72 ± 50% increase in CBF, and a 56 ± 19% decrease in OEF compared with baseline (P < 0.05). By 30 min postinsult and for the remainder of the study, there were no significant differences in CBF and OEF between control and insult groups, whereas CMRO₂ remained depressed throughout the 6-h postinsult period. This study demonstrates that NIRS can measure decreases in CMRO₂ caused by HI. The results highlight the potential for NIRS to be used in the neonatal intensive care unit to detect delayed brain damage.

deoxyhemoglobin; cerebral blood volume; indocyanine green; oxygen extraction fraction