Near-infrared spectroscopy measurement of oxygen extraction fraction and cerebral metabolic rate of oxygen in newborn piglets.

Cerebral metabolic rate of oxygen (CMRO2), the rate at which O2 is consumed in the brain by metabolic processes, is one of the most useful measures of normal brain function. The present study investigated the use of near-infrared spectroscopy (NIRS) in the noninvasive measurement of O2 extraction fraction (OEF) and CMRO2 in the newborn piglet. Indomethacin, although used successfully to effect closure of patent ductus arteriosus in the preterm infant, is known to cause transient reductions in cerebral blood flow (CBF) in both infant and adult humans and pigs. As a test of the NIRS method, the present study also examined the effect of indomethacin-induced reductions in CBF on both OEF and CMRO2. CBF, OEF, and CMRO2 were assessed in 20 newborn piglets, 0.2-3.0 d old. Ten piglets received 0.2 mg/kg of indomethacin infused over 30 min; remaining piglets received saline infusion as control. CBF, OEF, and CMRO2 measurements were performed before infusion and at 30-min intervals for a period of 90 min post-infusion. Saline infusion elicited no response in CBF, OEF, or CMRO2. Immediately after indomethacin infusion, CBF decreased 18.1% below (p < 0.05) and OEF increased 26.2% above (p < 0.05) pre-infusion values, whereas CMRO2 showed no significant changes throughout the study. Both CBF and OEF returned to baseline within 60 min after infusion of indomethacin. The proficiency of NIRS in the measurement of OEF and CMRO2 was demonstrated through the observation of transient increases in OEF, which served to maintain CMRO2 during indomethacin-induced reductions in CBF.