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Cerebral metabolic rate of oxygen and amplitude-integrated electroencephalography during early reperfusion after hypoxia-ischemia in piglets

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

Submitted 28 August 2008 ; accepted in final form 12 March 2009

The therapeutic window following perinatal hypoxia-ischemia is brief, and early clinical signs of injury can be subtle. Electroencephalography (EEG) represents the most promising early diagnostic of hypoxia-ischemia; however, some studies have questioned the sensitivity and specificity of EEG. The present study investigated the use of both near-infrared spectroscopy (NIRS) measurements of the cerebral metabolic rate of oxygen (CMRO₂) and amplitude-integrated EEG (aEEG) to detect the severity of hypoxia-ischemia after 1 h of reperfusion in newborn piglets (10 insult, 3 control). The CMRO₂ was measured before and after 1 h of reperfusion from hypoxia-ischemia, the duration of which was varied from piglet to piglet with a range of 3–24 min, under fentanyl/nitrous oxide anesthesia to mimic awake-like levels of cerebral metabolism. EEG data were collected throughout the study. On average, the CMRO₂ and mean aEEG background signals were significantly depressed following the insult (P < 0.05). Mean CMRO₂ and mean aEEG background were 2.61 ± 0.11 ml O₂·min^–1·100 g^–1 and 20.4 ± 2.7 µV before the insult and 1.58 ± 0.09 ml O₂·min^–1·100 g^–1 and 11.8 ± 2.9 µV after 1 h of reperfusion, respectively. Both CMRO₂ and aEEG displayed statistically significant correlations with duration of ischemia (P < 0.05; r = 0.71 and r = 0.89, respectively); however, only CMRO₂ was sensitive to milder injuries (<5 min). This study highlights the potential for combining NIRS measures of CMRO₂ with EEG in the neonatal intensive care unit to improve early detection of perinatal hypoxia-ischemia.

near-infrared spectroscopy; piglet; hypoxia-ischemia; electroencephalography