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 (CMRO(2)) 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 CMRO(2) 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 CMRO(2) and mean aEEG background signals were significantly depressed following the insult (P < 0.05). Mean CMRO(2) and mean aEEG background were 2.61 +/- 0.11 ml O(2).min(-1).100 g(-1) and 20.4 +/- 2.7 microV before the insult and 1.58 +/- 0.09 ml O(2).min(-1).100 g(-1) and 11.8 +/- 2.9 microV after 1 h of reperfusion, respectively. Both CMRO(2) and aEEG displayed statistically significant correlations with duration of ischemia (P < 0.05; r = 0.71 and r = 0.89, respectively); however, only CMRO(2) was sensitive to milder injuries (<5 min). This study highlights the potential for combining NIRS measures of CMRO(2) with EEG in the neonatal intensive care unit to improve early detection of perinatal hypoxia-ischemia.