Electrocortical brain activity, cerebral haemodynamics and oxygenation during progressive hypotension in newborn piglets

Objective: To investigate the relationships between systemic and cerebral haemodynamics and oxygenation, and electroencephalogram (EEG) amplitude and frequency analysis studied by the cerebral function analyzing monitor (CFAM) during progressive hypovolemic hypotension. Methods: Six piglets of 1 week of age, weighing 1.9–3.4 kg were mechanically ventilated under 1–1.5% halothane anaesthesia. After 1 h stabilization, blood was withdrawn in aliquots of 10 ml/kg over 15 min up to a total of 40–60 ml/kg. Arterial oxygenation was maintained at normal levels. Thereafter, the total blood volume previously withdrawn, was reinfused. Changes in near infrared spectroscopy (NIRS) parameters [cerebral oxidized cytochrome aa3 (Cytaa3), cerebral blood volume (CBV) or total haemoglobin (tHb: oxy- + deoxyhaemoglobin)], carotid blood flow (Qcar), maximal EEG amplitude and EEG frequency percentages were analyzed continuously. Results: The EEG amplitude remained stable until the mean arterial blood pressure (MAP), Qcar and tHb dropped below 30 mmHg (41% of baseline), 20 ml/min (33% of baseline) and 82% of baseline, respectively. Delta (δ) wave frequency percentage of the CFAM increased significantly at MAP below 30 mmHg. EEG amplitude remained depressed after blood reinfusion and haemodynamic recovery. Cytaa3 changes were not statistically significant, reflecting sufficient neuronal oxygenation. Conclusion: Our results show that electrocortical function is affected only by profound systemic hypotension. This occurred at a higher level of cerebral oxygen delivery than the level associated with neuronal hypoxia and secondary cell damage.