Cord Gas Analysis, Decision-to-Delivery Interval, and the 30-Minute Rule for Emergency Cesareans

Abstract

The so-called 30-minute rule is that hospitals having obstetric facilities should be equipped to perform an emergency cesarean delivery starting within 30 minutes of the decision to operate. This study examined the relationship between the results of umbilical arterial blood gas analysis and the decision-to-delivery interval in emergency cases with nonreassuring fetal status. Improved outcomes with an interval less than 30 minutes would presumably validate the rule. A retrospective cohort study included all cesarean deliveries done for this reason during a 16-month period in the years 2001 to 2003. Three specialists in maternal-fetal medicine, masked to the outcome, received a synopsis of clinical information that would have been available at the time of delivery as well as the last hour of the electronic fetal heart rate tracing. Emergent deliveries were done as soon as possible and deliveries within 30 minutes of the decision to operate. The series included 117 women, 34 classified as emergent and 83 as urgent. General anesthesia was given significantly more often in emergent cases and epidural anesthesia in urgent cases. The decision-to-delivery time was nearly 14 minutes less in the emergent group. There were no differences in 1- or 5-minute Apgar scores, but both the umbilical arterial pH and base excess were significantly worse in emergent cases. The decision-to-delivery interval was nearly 15 minutes shorter for general than for spinal anesthesia and 13 minutes less than with epidural anesthesia. Apgar scores recorded at 5 minutes (but not at 1 minute) were significantly increased with general anesthesia. Umbilical artery pH values did not differ significantly between groups, but base excess was significantly less favorable with general anesthesia. An increased decision-to-delivery interval correlated with improved umbilical arterial pH and base excess. This correlation did not help to predict when the fetus would develop metabolic acidosis severe enough to increase the risk of long-term neurologic morbidity. A very large majority of fetuses had normal values even after 30 minutes. Seven premature infants had intraventricular hemorrhage; 6 of them survived. Only fair to moderate agreement was found between the 3 specialists. Metabolic acidosis is not sensitively predicted by electronic fetal monitoring. In this study, blood gas values remained normal even when birth took place more than 30 minutes after the decision to operate. In the presence of nonreassuring fetal monitoring, the 30-minute rule is a compromise that does not precisely predict how much time will pass before severe metabolic acidosis develops.