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

Introduction

Impaired oxidative metabolism after hypoxia-ischemia (HI) is believed to be an indicator of delayed brain injury ¹ . We have recently developed a near-infrared spectroscopy (NIRS) technique that could be used to measure the cerebral metabolic rate of oxygen (CMRO2) at the bedside of the critically ill newborn. The CMRO2 measurement requires a combination of indocyanine green-based measurements of cerebral blood flow (CBF) and measurements of cerebral deoxy-hemoglobin concentration^{2, 3}. The objective of this experiment was to investigate the ability of NIRS to measure changes in CMRO2 following HI in newborn piglets as a prerequisite to clinical investigation.

Methods

Nine piglets were subjected to 30 minutes 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 and CMRO2 were acquired at baseline, every 30 minutes for the first 2 hours after the insult, and on the hour for the following 4 hours.

Results

Figures 1 and 2 display the CBF and CMRO2 measurements, respectively, for each group of piglets throughout the experiment. The solid line represents the control group, the dashed line represents the hypoxic-ischemic group and the shaded region represents the duration of HI. Only CMRO2 showed a persistent change following HI. Five minutes after reoxygenation, there was a 28 +/− 12 % decrease in CMRO2 and a 72 +/− 50% increase in CBF compared to baseline (p < 0.05). CBF returned to baseline by 30 minutes post-insult and did not change for the remainder of the study, whereas, CMRO2 was depressed for the remainder of the study.

Figure 1 Figure 2

Conclusion

We have demonstrated that NIRS can measure persistent decreases in CMRO2 following HI, despite the return of CBF to baseline within 30 minutes post-insult. The results infer a potential for NIRS to be used in the neonatal intensive care unit to detect early signs of delayed brain injury.