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

OBJECTIVE: Increasing frequency of severe variable decelerations is associated with acidemia. However, there is little understanding of its development or normalization rate. STUDY DESIGN: 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. RESULTS: 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). CONCLUSION: 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.