Measures of acidosis with repetitive umbilical cord occlusions leading to fetal asphyxia in the near-term ovine fetus.

Abstract

Increasing frequency of severe variable decelerations is associated with acidemia. However, there is little understanding of its development or normalization rate. To quantify the time course of acidemia, 10 near-term fetal sheep underwent a series of mild (1 minute every 5 minutes), moderate (1 minute every 3 minutes), and severe (1 minute every 2 minutes) umbilical cord occlusions (UCO), lasting 1 hour each or until fetal arterial pH decreased to less than 7.00. Each minute of UCO resulted in base deficit (BD) and lactate increases at rates of 0.56 and 0.35 mmol/L per minute, respectively. During a 2 h recovery, BD and lactate normalized at rates of 0.09 and 0.04 mmol/L per minute. BD correlated highly with lactate (r = 0.95; P < .001). Our findings in the near-term ovine fetus suggest that the knowledge of fetal BD deterioration and recovery rates can aid assessing fetal acidemia during labor.