Fetal oxygen consumption, umbilical circulation and electrocortical activity transitions in fetal lambs

Chronically instrumented fetal lambs were employed to test the hypothesis that the high voltage electrocortical activity phase is a state of low fetal oxygen consumption compared with the low voltage electrocortical activity phase. Measurements of umbilical flow (electromagnetic flowmeter) together with oxygen saturations and haemoglobin concentration of umbilical venous and arterial blood were used to calculate oxygen consumption. Significant depression of umbilical flow occurred at the transition from low voltage electrocortical activity to high voltage electrocortical activity; the maximum change averaged 14% 2 min after the onset of the high voltage phase. Significant depressions of oxygen saturation in umbilical venous and arterial blood were found within 5 min of the onset of high voltage electrocortical activity, averaging 2.2% and 5.2% respectively. No depression of oxygen consumption was found during these transient changes in early high voltage electrocortical activity, as the venous-arterial oxygen content difference widened significantly as a consequence of a greater fall in umbilical arterial oxygen content (0.7 ml/dl) than in umbilical venous oxygen content (0.3 ml/dl). Overall, we detected no significant depression of oxygen consumption in high voltage electrocortical activity. However a small but significant depression of oxygen consumption (6%) was found late in the high voltage electrocortical activity phase when the level of oxygen consumption in low voltage electrocortical activity was greater than 7 ml/min per kg. We conclude that the high voltage electrocortical activity in fetal lambs is not associated with a marked depression of oxygen consumption, despite significant transient depressions of umbilical flow and oxygen levels in umbilical venous and arterial blood. When oxygen consumption in the low voltage electrocortical activity is high, small depressions of oxygen consumption are present late in the high voltage electrocortical activity phase.