Cerebral impedance and neurological outcome following a mild or severe hypoxic/ischemic episode in neonatal piglets

Multi-frequency bio-impedance has the potential to identify infants at risk of poor neurodevelopmental outcome following hypoxia by detecting cerebral edema. This study investigated the relationship between the severity of an hypoxic/ischemic episode, neurological outcome following the hypoxia and non-invasively measured cerebral bioelectrical impedance in piglets. One-day-old piglets were anaesthetised and ventilated. Hypoxia was induced by reducing the inspired oxygen concentration to 3-5%. Severe hypoxia was defined as hypoxia resulting in at least 30 min of low amplitude EEG (<5 microV) as well as hypotension and acidosis. Cerebral bio-impedance was measured before, during and for up to 6 h post-hypoxia. Neurological outcome was determined by a neurology score at 24 and 48 h after hypoxia, and by histological examination of the brain at 72 h. There was no increase in cerebral impedance in control animals. Following mild hypoxia cerebral impedance increased transiently. Following severe hypoxia, cerebral impedance increased and remained elevated. Cerebral impedance following severe hypoxia was significantly higher than after mild hypoxia at 10 min and from 2 to 6 h after resuscitation. Cerebral impedance measurements made up to 1 h and between 3 and 6 h after resuscitation were significantly correlated with neurological outcome. Results indicate that non-invasive cerebral impedance measurements are able to discriminate early between those individuals who have suffered a mild, acute hypoxic episode, and those who have suffered a severe hypoxic episode. The technique has the potential to predict which individuals will have a poor neurological outcome.