Somatosensory evoked potential and brain water content in post-asphyxic immature piglets

Depression of somatosensory evoked potentials (SEP) after a single episode of complete asphyxia with near cardiac arrest was evaluated to determine whether persistent SEP depression is related to postresuscitation edema in cortical gray matter or subcortical white matter. Piglets (< 7 d of age) were anesthetized with sodium pentobarbital and fentanyl. Asphyxia was produced by occlusion of the endotracheal tube for 7 min. Arterial O2 saturation fell to 5%. Resuscitation was achieved in < 2 min with ventilation, epinephrine, and chest compressions. Regional brain water content was determined from the difference between wet and dry weight. Two control groups were also analyzed; one immediately after (n = 5) and one 6 h after induction (n = 7) of anesthesia. SEP amplitude became isoelectric during asphyxia and recovered to 50 +/- 13% (n = 7) of baseline 6 h after resuscitation. In the 6-h control group, SEP amplitude remained above baseline. The percent water content (mean +/- SEM) among the three groups (asphyxia versus time control versus brief anesthesia control) was not different in the cortical gray matter (83.0 +/- 0.7% versus 82.4 +/- 0.4% versus 83.2 +/- 0.3%) or subcortical white matter (75.6 +/- 0.8% versus 74.8 +/- 0.9% versus 75.6 +/- 0.5%). In seven other piglets, cerebral blood flow and O2 consumption recovered to baseline by 1 h after asphyxia. Therefore, we found that the sustained depression of SEP amplitude, after 7 min of asphyxia in immature piglets, is not related to brain edema or persistent decreases in global cerebral O2 consumption.