Cerebral function monitor (CFM) recording is a simplified amplitude integrated electroencephalogram (EEG) registration. Cerebral function analysing monitor (CFAM) analyses the EEG frequency content. The CFM and CFAM were recorded by a two-channel EEG from one frontal and two partietal electrodes. The aim of this work was to study the effects of progressive hemorrhagic hypotension on electrocortical brain activity and cerebral tissue oxygenation measured with near infrared spectroscopy (NIRS). Six piglets aged one week, weighing 1.9 to 3.4 kg were mechanically ventilated with O2/N2 mixture under 1 to 2% halothane anaesthesia. A 6 mm precalibrated ultrasonic transit time transducer was placed around the right carotid artery. A 4 French fiber optic catheter was placed in the right femoral artery and the tip was advanced into the abdominal aorta for registration of oxygen saturation and blood pressure. In order to induce progressive hypotension, blood was withdrawn in aliquots of 10 ml/kg over 15 minutes up to a total of 40 to 60 ml/kg. Arterial oxygenation was maintained at normal levels. Changes in cerebral oxydized cytochrome aa3 (cytaa3), cerebral blood volume or total hemoglobin (HbT:oxy- + deoxyhemoglobin), carotid blood flow (Qcar), maximal electrocortical brain activity and EEG frequencies percentages were analysed continuously at decreasing mean arterial blood pressure (MAP). Cytaa3 and maximal power of electrocortical brain activity remained stable until MAP and Qcar dropped below 30 mmHg (41% of baseline) and 20 ml/min (33% of baseline) respectively. MAP and delta wave frequency percentage of the EEG showed a negative significant correlation (p<0.001). Delta wave increased at MAP below 45 mmHg (63% of baseline) and preceded changes in other CFM and NIRS parameters. We conclude that EEG frequency distribution depicted by CFAM might offer the possibility to anticipate critical changes in cortical activity and that could help to establish a proper direction when applied clinically in severe ill newborns.
