ACID ACCUMULATION DURING END-STAGE BRADYCARDIA IN TERM FETUSES - HOW LONG IS TOO LONG

Objective To estimate the existence and degree of fetal accumulation o f acid during end-stage bradycardia as reflected by the base deficit. This may set a criterion for proper intervention during labour. Settin g Maternity unit of the Tel Aviv Medical Centre. Subjects Forty-three consecutively born term infants whose mothers were delivered by vacuum extraction were analysed: 27 because of end-stage bradycardia and 16 controls whose mothers were delivered electively because of maternal i ndications. Main outcome measures Analysis of umbilical arterial cord blood for pH, PCO2 and base deficit. The base deficit was compared bet ween the groups using the two-tailed Student's t test, and was correla ted with variables of fetal heart rate monitoring using the Pearson co rrelation coefficient. Results The base deficit was greater in newborn s who had end-stage bradycardia than in controls (11.02 vs 5.01, P < 0 .0001). The duration of loss of short term variability in fetal heart rate during end-stage bradycardia correlated positively with the base deficit (r = 0.8, P < 0.0005). Conversely, the time until the loss of short term variability during end-stage bradycardia correlated negativ ely with the base deficit. The length and the depth of the bradycardia and their product, had a weaker correlation with the base deficit. Co nclusions End-stage bradycardia, which presumably reflects fetal hypox ia, is associated with acidaemia in the umbilical artery at birth in s ome fetuses. The fetuses who are predisposed to acidaemia, as reflecte d by an increased base deficit, are those who lost their fetal heart r ate variability during end-stage bradycardia for more than 4 min or st arted to lose this in less than 3 min from the beginning of the end-st age bradycardia. Operative vaginal delivery should be reserved for the se indications.