Measurement of Cerebral Oxidative Metabolism with Near-Infrared Spectroscopy: A Validation Study

Abstract

Predicting the onset of secondary energy failure after a hypoxic–ischemic insult in newborns is critical for providing effective treatment. Measuring reductions in the cerebral metabolic rate of oxygen (CMRO₂) may be one method for early detection, as hypoxia–ischemia is believed to impair oxidative metabolism. We have developed a near-infrared spectroscopy (NIRS) technique based on the Fick Principle for measuring CMRO₂. This technique combines cerebral blood flow (CBF) measurements obtained using the tracer indocyanine green with measurements of the cerebral deoxy-hemoglobin (Hb) concentration. In this study, NIRS measurements of CMRO₂ were compared with CMRO₂ determined from the product of CBF and the cerebral arteriovenous difference in oxygen measured from blood samples. The blood samples were collected from a peripheral artery and the sagittal sinus. Eight piglets were subjected to five cerebral metabolic states created by varying the plane of anesthesia. No significant difference was found between CMRO₂ measurements obtained with the two techniques at any anesthetic level ( P > 0.5). Furthermore, there was a strong correlation when concomitant CMRO₂ values from the two techniques were compared ( R² = 0.88, P< 0.001). This work showed that CMRO₂ can be determined accurately by combining NIRS measurements of CBF and Hb. Since NIRS is safe and measurements can be obtained at the bedside, it is believed that this technique could assist in the early diagnosis of cerebral energy dysfunction after hypoxia–ischemia.