OXYGEN-CONSUMPTION, ACID-BASE STATUS, AND BEHAVIOR DURING AND AFTER ACUTE, SEVERE HEMORRHAGE IN FETAL LAMBS

The metabolic and behavioral effects of 40-45% hemorrhage (at similar to 1%/min) were studied in nine fetal lamds in utero (130-135 days of gestation) until 2 days posthemorrhage. Umbilical blood flow (Q(um)) f ell from 192 +/- 14 to 100 +/- 9 ml . min(-1) . kg(-1) at the end of b lood loss, and on the day of hemorrhage it was linearly related to blo od volume. However, on the posthemorrhage days, Q(um) was restored eve n though blood volume was still reduced. Fetal O-2 delivery (DO2) fell with the decrease in Q(um) and later due to anemia (decrease in hemat ocrit from 33.4 +/- 1.2 to 23.6 +/- 1.2%), from 946 +/- 81 to 494 +/- 47 mu mol . min(-1) . kg(-1), but the decrease was lessened because of a rise in umbilical venous PO2 (31.7 +/- 2.6 to 45.9 +/- 2.8 mmHg). F etal O-2 consumption was reduced during and for 2 h after hemorrhage ( 262 +/- 17 to 190 +/- 16 mu mol . min(-1) . kg(-1)), and this was asso ciated with modest lactic acidemia (1.25 +/- 0.11 to 2.91 +/- 0.43 mM) . There was also a temporary reduction in fetal breathing activity, lo w voltage electrocortical state, and rapid eye movements, but this was not associated with hypoxemia. It is concluded that reductions in fet al DO2 achieved via fetal blood loss are better tolerated than during hypoxemia and that the associated depression in fetal biophysical acti vities involves mechanisms other than systemic hypoxia.